is metallic Silver, reduced from the soluble Nitrate upon the plates.

Some operators add pure Nitrate of Potash to this developing solution, to
form a _small portion_ of Protonitrate of Iron. It is said to improve the
colour slightly. The proportions are 10 grains of Nitrate of Potash to
about 14 or 15 grains of Protosulphate of Iron.

_Formula No. 2._--In this formula, if the colour of the image is not
sufficiently white, try the effect of increasing the amount of Nitric Acid
slightly. On the other hand, if the development is imperfect in parts,
and patches of a green colour are seen, use _three grains_ of Pyrogallic
Acid to the ounce, with less Nitric Acid. A few drops of Nitrate of Silver
solution added to the Pyrogallic, immediately before use, will augment the
energy of development when blue and green spots occur.

_Formula No. 3_, or Protonitrate of Iron, does not require any addition
of Acid; but it will be advisable, in some cases, to add to it a few
drops of Nitrate of Silver immediately before developing. It gives a
bright metallic image, resembling that obtained by adding Nitric Acid to
Protosulphate of Iron.

The following process is commonly followed for preparing Protonitrate of
Iron:--

Take of Nitrate of Baryta 300 grains;--powder and dissolve by the aid of
heat in three ounces of water. Then throw in by degrees, with constant
stirring, crystallized Sulphate of Iron, _powdered_, 320 grains. Continue
to stir for about five or ten minutes. Allow to cool, and filter from the
white deposit, which is the insoluble Sulphate of Baryta.

In place of Nitrate of Baryta, the Nitrate of Lead may be used (Sulphate
of Lead being an insoluble salt), but the quantity required will be
different. The atomic weights of Nitrate of Baryta and Nitrate of Lead are
as 131 to 166; consequently 300 grains of the former are equivalent to 380
grains of the latter.

THE FIXING SOLUTION.

  Cyanide of Potassium                     2 to 12 grains.
  Common Water                             1 fluid ounce.

Cyanide of Potassium is usually preferred to Hyposulphite of Soda for
fixing direct Positives; it is less liable to injure the purity of the
white colour. The percentage of _Carbonate of Potash_ in commercial
Cyanide of Potassium is so variable that no exact directions can be given
for the formula. It is best however to use it rather dilute--of such a
strength that the plate is cleared gradually in from half a minute to a
minute.

The solution of Cyanide of Potassium decomposes slowly on keeping, but
it will usually retain its solvent power for several weeks. In order to
escape inconvenience from the pungent odour evolved by this salt, many
employ a vertical Bath to hold the solution; but in that case the plates
must be carefully washed before fixing, as the Iron salts hasten the
decomposition of the Cyanide.

THE WHITENING SOLUTION.

  Bichloride of Mercury                   30 grains.
  Distilled Water                          1 fluid ounce.

By a gentle application of heat the corrosive sublimate dissolves and
forms a solution as nearly as possible saturated at common temperatures.
The addition of a portion of Muriatic Acid enables the water to take up a
larger quantity of Bichloride; but this concentrated solution, at the same
time that it whitens more quickly than the other, is apt to act unequally
upon different parts of the image.

Before applying the Bichloride, the image is to be fixed and the plate
well washed. Either the Protosulphate of Iron or the Pyrogallic Acid with
Acetic (p. 223) may be used for the development; but the whitening process
is more rapid and uniform in the latter case.

SECTION II.

_Formulæ, etc., for Negative Solutions._[34]

[34] The same Collodion and Nitrate Bath may be used both for Positives
and Negatives if required; but there are a few minor points of difference
which are included in the following remarks.

THE COLLODION.

FORMULA No. 1.

  Purified Ether, sp. gr. ·720             5 fluid drachms.
  Purified Alcohol, sp. gr. ·825           3 fluid drachms.
  Soluble Pyroxyline                       4 to 8 grains.
  Pure Iodide of Cadmium or Ammonium       4 to 5 grains.

FORMULA No. 2.

  Rectified Ether, sp. gr. ·750            6 fluid drachms.
  Alcohol, sp. gr. ·836                    2 fluid drachms.
  Soluble Pyroxyline                       4 to 8 grains.
  Iodide of Potassium or Ammonium          4 grains.

When the Collodion and Iodizing mixture are kept separate, the second
formula will stand thus:--

  Rectified Ether ·750                     3 fluid ounces.
  Alcohol of ·836                          2 fluid drachms.
  Pyroxyline                              15 to 30 grains.

To each fluid ounce of this plain Collodion add 2 fluid drachms of the
following Iodizing solution:--

  Alcohol, sp. gr. ·836                    1 fluid ounce.
  Iodide of Potassium                     20 grains.

When the temperature of the Nitro-Sulphuric Acid used in making the
Pyroxyline is high (140° to 155°), it often happens that the Collodion is
too fluid with 4 grains of soluble paper to the ounce, and forms a blue
transparent film of Iodide on dipping the plate in the Bath. In that
case, increase the quantity of Pyroxyline from 4 grains to 6, or even to 8
grains to each ounce.

If the Collodion is glutinous, and produces a wavy surface, with less than
4 grains of Pyroxyline to the ounce, it is probable that the Alcohol is
too weak, or that the soluble Cotton is badly made.

If flakes of Iodide of Silver are seen loose upon the surface of the film,
and falling away into the Bath, the Collodion is over-iodized, and it will
be impossible to obtain a good picture.

After the Collodion has been employed to coat a number of plates, the
relative proportions of Alcohol and Ether contained in it become changed,
from the superior volatility of the latter fluid: when it ceases to flow
readily, and gives a more dense film than usual, thin it down by the
addition of a little rectified Ether.

In dissolving the Pyroxyline, any fibrous or flocculent matter which
resists the action of the Ether, must be allowed to subside, the clear
portion being decanted for use. The Iodide of Potassium is to be finely
powdered, and digested with the spirit until dissolved; it is better not
to apply any heat. Both Iodide of Ammonium and Iodide of Cadmium dissolve
almost immediately, if the salts are pure.

The Collodion must be kept in a cool and dark place. When prepared with
Iodide of Ammonium or Potassium it becomes at length high coloured and
insensitive. The free Iodine may then be removed by a strip of pure zinc
or silver-foil.

When sensitiveness is not an object, many prefer working with an old,
coloured Collodion, finding that it gives more intensity. It has been
shown at page 97 that a peculiar change takes place in Collodion after
iodizing, by which the intensity of the image is increased.

_Directions for using Glycyrrhizine in Collodion._--The action of this
material has been described at page 114. The Collodion should be iodized
with the Iodide of Cadmium only, or with a mixture of the Iodides and
Bromides of the alkalies. The condition which calls for the employment of
Glycyrrhizine is that often found in a newly made and rather glutinous
Collodion, viz. sensitiveness of film, with good half-tones, but
insufficient intensity in the high lights. Dissolve the Glycyrrhizine
in Alcohol (not Methylated) in the proportion of 5 grains to the ounce:
this solution may perhaps keep unchanged for three or four months. To
each ounce of the Collodion add from one to four drops, and expose in the
Camera a few seconds longer than before. The effect of the Glycyrrhizine
upon the Collodion may not be fully produced immediately; if so, the fluid
must be set aside for twenty-four hours.

_Use of Nitro-glucose in Collodion._--Nitro-glucose is a substance
analogous to Pyroxyline, but more unstable. When added to Collodion
iodized with the alkaline Iodides, it slowly decomposes, liberates Iodine,
lessens the sensitiveness to a certain extent, and confers intensity. Like
Glycyrrhizine, it may be used to remedy feebleness of the image, and to
give opacity to the blacks. Prepare the Nitro-glucose by the directions
given in the Vocabulary, Part III. Dissolve twenty grains in an ounce of
pure spirit, and agitate with powdered chalk to remove free acid. Add from
five to eight drops to each ounce of Collodion. In a few days, more or
less, according to temperature, the Collodion will deepen in colour, and
will be found on trial to produce a more vigorous picture.

_Collodion for hot Climates._--In this case the Iodide of Ammonium should
be avoided, as unstable and prone to change colour. Iodide of Cadmium
may be substituted, which has been shown to remain quite colourless when
dissolved in Alcohol and Ether.

Collodion iodized with the Iodide of Potassium will usually keep for about
six weeks or two months; but no certain rule can be given, much depending
upon the condition of the Ether and the heat of the weather.

Plain Collodion may retain its properties unimpaired for five or six
months, sometimes much longer; but there is a tendency to a formation of
the acid principle (p. 85); and hence, on the addition of an alkaline
Iodide to old Collodion, the coloration is commonly very rapid. The
structure of the transparent film may also be injured by keeping plain
Collodion for too long a time.

Photographers who wish to operate with Collodion in hot climates will
find it advantageous to carry with them the prepared Pyroxyline and the
spirituous solvents, observing that the bottles are carefully _luted_,
and that a bubble of air is left in the neck of each, to allow for the
necessary expansion, which might otherwise burst the glass or force out
the stopper.

THE NITRATE BATH.

This solution may be prepared by the same formula as that given for
direct Positives at page 203, acidifying the solution with Acetic Acid in
preference to Nitric Acid.

THE DEVELOPING SOLUTION.

  Pyrogallic Acid                      1 grain.
  Acetic Acid (glacial)               10 to 20 minims,
    or Beaufoy's Acetic Acid fort.     1 fluid drachm.
  Alcohol                             10 minims.
  Distilled Water                      1 fluid ounce.

In place of Distilled Water, pure Rain-Water may be used (see Part III.,
Art. "Water").

The quantity of Acetic Acid required will vary with the strength of
the Acid and the temperature of the atmosphere. An excess enables the
manipulator to cover the plate more easily before the action begins, but
when the picture is taken in a dull light, is apt to give a bluish, inky
hue to the image. In cold weather, use less of the Acetic and twice the
quantity of Pyrogallic Acid. With Collodion prepared from Spirits nearly
anhydrous, and iodized with Iodide of Cadmium, the full quantity of Acetic
Acid will be required, as there is sometimes a little difficulty in
making the developer flow up to the edge of the film.

If the image cannot be rendered sufficiently black, two or three minims of
the Nitrate Bath solution may be added to each drachm towards the end of
the development.

If the solution be kept for some time after its first preparation, it
becomes brown and discoloured. In this state it will still develope the
image, but is less likely to give a clear and vigorous picture. A solution
of Pyrogallic Acid in Acetic Acid will keep for many weeks, and may be
diluted down when required for use.

The following is a good formula:--

  Pyrogallic acid                    12 grains.
  Beaufoy's Acetic acid               1 fluid ounce.

To one drachm add seven drachms of water.

THE FIXING LIQUID.

  Cyanide of Potassium                2 to 12 to 20 grains.
  Water                               1 fluid ounce.

  or, Hyposulphite of Soda            1/2 ounce.
  Water                               1 fluid ounce.

For remarks on the Cyanide of Potassium Fixing Bath, see the last Section,
page 207.

CHAPTER III.

MANIPULATIONS OF THE COLLODION PROCESS.

These may be classed under five heads:--Cleaning the Plates.--Coating with
Iodide of Silver.--Exposure in the Camera.--Developing the image.--Fixing
the image.--In addition to this, the present Chapter will include in
separate Sections directions for the choice and management of lenses, for
copying engravings, manuscripts, etc., and for taking stereoscopic and
microscopic photographs.

CLEANING THE GLASS PLATES.

Care should be taken in selecting glass for use in Photography. The
ordinary window-glass is inferior, having scratches upon the surface, each
of which may cause an irregular action of the developing fluid; and the
squares are seldom flat, so that they are apt to be broken in compression
during the printing process.

The patent plate answers better than any other description of glass; but
if it cannot be procured, the "flatted crown glass" may be substituted.

Before washing the glasses, each square should be roughened on the edges
by means of a file or a sheet of emery-paper; or more simply, by drawing
the edges of two plates across each other. If this precaution be omitted,
the fingers are liable to injury, and the Collodion film may contract and
separate from the sides.

In cleaning glasses, it is not sufficient, as a rule, to wash them simply
with water; other liquids are required to remove _grease_, if present. A
cream of Tripoli powder and Spirits of Wine, with a little Ammonia added,
is commonly employed. A tuft of cotton is dipped in this mixture, and the
glasses are well rubbed with it for a few minutes. They are then rinsed in
plain water and wiped dry with a cloth.

The cloths used for cleaning glasses should be kept expressly for that
purpose; they are best made of a material sold as fine "diaper," and very
free from flocculi and loosely-adhering fibres. They are not to be washed
_in soap and water_, but always in pure water or in water containing a
little Carbonate of Soda.

After wiping the glass carefully, complete the process by polishing with
an old silk handkerchief, avoiding contact with the skin of the hand.
Some object to _silk_, as tending to render the glass electrical, and so
to attract particles of dust, but in practice no inconvenience will be
experienced from this source.

Before deciding that the glass is clean, hold it in an angular position
and _breathe_ upon it. The importance of attending to this simple rule
will be at once seen by referring to the remarks made at page 39. In the
Honey preservative and Collodio-Albumen processes it is especially needful
that the glasses should be thoroughly cleaned, on account of the tendency
which the film has to become loosened or to blister during the development
and washings. Caustic Potash, sold by the druggists under the name of
"Liquor Potassæ," is very efficacious, or in place of it, a warm solution
of "washing Soda" (Carbonate of Soda). Liquor Potassæ, being a caustic and
alkaline liquid, softens the skin and dissolves it; it must therefore be
diluted with about four parts of water and applied to the glass by means
of a cylindrical roll of flannel. After wetting both sides thoroughly,
allow the glass to stand for a time until several have been treated in the
same way; then wash with water and rub dry in a cloth.

The use of an alkaline solution is usually sufficient to clean the glass,
but some plates are dotted on the surface with small white specks, not
removable by Potash. These specks may consist of hard particles of
_Carbonate of Lime_, and when such is the case they dissolve readily in
a dilute acid,--Oil of Vitriol, with about four parts of water added, or
dilute Nitric Acid.

The objection to the use of Nitric Acid is, that if allowed to come in
contact with the dress, it produces stains which cannot be removed unless
_immediately_ treated with an alkali. A drop of Ammonia should be applied
to the spot before it becomes yellow and faded.

When Positives are to be taken, it is advisable to use additional care in
preparing the glass, and especially so with pale transparent films and
neutral, Nitrate Bath.

After a glass has been once coated with Collodion, it is not necessary in
cleaning it a second time to use anything but pure water; but if the film
has been allowed to harden and become dry, possibly dilute Oil of Vitriol
or Cyanide of Potassium may be required to remove stains.

When glasses have been repeatedly used in photography they often become at
length so dull and stained, that it is better to reject them.

COATING THE PLATE WITH THE COLLODIO-IODIDE OF SILVER.

This part of the process, with that which follows, must be conducted in
a room from which chemical rays of light are excluded. It is inferred
therefore that the operator has provided himself with an apartment of that
kind.

The most simple plan of preparing the room is to nail a treble thickness
of yellow calico completely over the window, or a part of it, the
remainder being darkened. To this a single thickness of a waterproof
material made by coating linen with gutta-percha may be added as a further
security against the entrance of white light, the smallest pencil of which
admitted into the room would cause fogging.

It is often convenient to illuminate by means of a candle screened
by yellow glass. A dark orange yellow, approaching to brown, is more
impervious to chemical rays than a lighter canary-yellow. Lamps suitable
for the purpose are sold by the manufacturers of apparatus and chemicals.

Before coating the plate with Collodion, see that the fluid is perfectly
clear and transparent, and that all particles have settled to the bottom;
also that the neck of the bottle is free from hard and dry crusts, which,
if allowed to remain, would partially dissolve and produce striæ upon the
film. In taking small portraits and stereoscopic subjects, these points
are of especial importance, and every picture will be spoiled if they are
not attended to.

A useful piece of apparatus for clearing Collodion is that represented in
the following woodcut.

The Collodion, having been iodized some hours previously, is allowed to
settle down and become clear in this bottle; then by gently blowing at
the point of the shorter tube, the small glass siphon is filled, and the
fluid drawn off more closely than could be done by simply pouring from one
bottle to another.

When the Collodion is properly cleared from sediment, the operator takes
a glass plate, previously cleaned, and wipes it gently with a silk
handkerchief, in order to remove any particles of dust which may have
subsequently collected. If it be a plate of moderate size, it may be
held by the corners in a horizontal position, between the forefinger and
thumb of the left hand. The Collodion is to be poured on steadily until a
circular pool is formed, extending nearly to the edges of the glass.

By a slight inclination of the plate the fluid is made to flow towards the
corner marked 1, in the above diagram, until it nearly touches the thumb
by which the glass is held: from corner 1 it is passed to corner 2, held
by the forefinger; from 2 to 3, and lastly, the excess poured back into
the bottle from the corner marked No. 4. It is then to be held vertically
over the bottle for a moment, until it _nearly_ ceases to drip, and then,
by raising the thumb a little, the direction of the plate is changed,
so as to cause the diagonal lines to coalesce and produce a smooth
surface. The operation of coating a plate with Collodion must not be done
hurriedly, and nothing is required to ensure success but steadiness of
hand and a sufficiency of the fluid poured in the first instance upon the
plate.

In coating larger plates, the _pneumatic_ holder, which fixes itself by
suction, will be found the most simple and useful.

_The Proper Time for immersing the Film in the Bath._--After exposing a
layer of Collodion to the air for a short time, the greater part of the
Ether evaporates, and leaves the Pyroxyline in a state in which it is
neither wet nor dry, but receives the impression of the finger without
adhering to it. Photographers term this _setting_, and when it takes
place it is a sign that the time has come for submitting it to the action
of the Bath.

If the film be lowered into the Nitrate before it has set, the effect is
the same as that produced by adding Water to Collodion. The Pyroxyline is
precipitated in part, and consequently there are cracks, and the developer
will not always run up to the edge of the film. On the other hand, if
it be allowed to become too dry, the Iodide of Silver does not form
perfectly, and the film, on being washed and brought out to the light,
exhibits a peculiar iridescent appearance, and is paler in some parts than
in others.

No rule can be given as to the exact time which ought to elapse: it varies
with the temperature of the atmosphere, and with the proportions of Ether
and of Pyroxyline; thin Collodion containing but little Alcohol requiring
to be immersed more speedily. Twenty seconds in the common way, or ten
seconds in hot weather, will be found an average time.

When the plate is ready, rest it upon the glass dipper, Collodion side
uppermost, and lower it into the solution by a slow and steady movement:
if any pause be made, a horizontal line corresponding to the surface
of the liquid will be formed. Then place the cover upon the vertical
trough[35] and darken the room, if this has not already been done. As
the presence of white light does no injury to the plate previous to its
immersion in the Bath, it is not necessary to exclude it during the time
of coating with Collodion.

[35] Troughs made of gutta-percha, glass, or porcelain are commonly used;
the latter are the best, being quite opaque and not liable to cracks or
leaking.

When the plate has remained in the solution about twenty seconds, lift
it partially out two or three times, in order to wash away the Ether
from the surface. An immersion of one minute to a minute and a half will
usually be sufficient; or two minutes in cold weather, and with Collodion
containing but little Alcohol. Continue to move the plate until the liquid
flows off in a uniform sheet, when the decomposition may be considered
to be sufficiently perfect. The principal impediment in this part of the
process lies in the difficulty with which Ether and Water mix together,
which causes the Collodion surface on its first immersion to appear oily
and covered with streaks. By gentle motion the Ether is washed away, and a
smooth and homogeneous layer obtained.

The plate is next removed from the dipper, and held vertically in the hand
for a few seconds upon blotting paper, to drain off as much as possible of
the solution of Nitrate of Silver.[36] It is then wiped on the back with
filtering-paper, placed in a clean and dry slide, and is ready for the
Camera.

[36] This blotting-paper must be frequently changed, or stains will be
produced at the lower edge of the plate during the development.

The amateur is strongly recommended not to proceed to take pictures in the
Camera until by a little practice he has succeeded in producing a perfect
film which is uniform in every part and will bear inspection when washed
and brought out to the light.

It should, if properly prepared, present the following appearance:--Smooth
and uniform, both by reflected and transmitted light; free from wavy
lines or markings such as would be caused by a glutinous Pyroxyline, and
from opaque dots due to small particles of dust or Iodide of Silver in
suspension in the Collodion.

The evidences of a too rapid immersion in the Bath are sought for on the
side of the plate from which the Collodion was poured off. This part
remains wet longer than the other, and always suffers the most; horizontal
cracks or marks resembling vegetation are seen, each of which would cause
an irregular action of the developing fluid. On the other hand, the upper
part of the plate must be examined for the pale colour characteristic of
a film which had become too dry before immersion, since the Collodion is
thinner at that point than at any other.

EXPOSURE OF THE PLATE IN THE CAMERA.

After the plate has been rendered sensitive, it should be exposed and
developed with all convenient despatch; the intensity of the Negatives
being, with some Collodion, materially lessened by neglecting this point
(see p. 100).

Ascertain that the joints of the Camera are tight in every part--that the
sensitive plate, when placed in the slide, falls precisely in the same
plane as that occupied by the ground glass--and that the chemical and
visual foci of the Lens accurately correspond.[37]

[37] See the Second Section of this Chapter.

Supposing the case of a portrait, next proceed to arrange the sitter
as nearly as possible in a vertical position, that every part may be
equidistant from the lens. Then, an imaginary line being drawn from the
head to the knee, point the Camera slightly downwards, so that it may
stand at right angles to the line. If this point be neglected the figure
will be liable to be distorted in a manner presently to be shown (p. 228).

In order to succeed well with portraits, the sitter should be illuminated
by an even, diffused light falling horizontally. A vertical light causes a
deep shadow on the eyes and makes the hair appear grey: it must therefore
be cut off by a curtain of blue or white calico suspended over the head.
The direct rays of the sun are generally to be avoided, as causing too
great a contrast of light and shade. This is a point on which the operator
must exercise his judgment. With a feeble Collodion, a better Negative
picture may often be obtained by placing the sitter quite in the open air,
but when the Collodion and Bath are in the condition for giving great
intensity of image, the gradation of tone will be inferior unless the
light be prevented from falling too strongly upon the face and hands.

In focussing the object, cover the head and the back part of the Camera
with a black cloth, and shift the Lens gently until the greatest possible
amount of distinctness is obtained. Then insert the sensitive plate, and
having raised the door of the slide, cover all with a black cloth during
the exposure, as a security against white light finding entrance at any
part excepting through the Lens.

With regard to the proper time for the exposure, so much depends upon the
brightness of the light and the nature of the Collodion, that it must be
left almost entirely to experience. The following general rules however
may be of use:--

In a tolerably bright day in the spring or summer months, and with a
newly-mixed Collodion, allow four seconds for a Positive Portrait, and
eight seconds for a Negative. With a double-combination Lens of large
aperture and short focus, perhaps three seconds, and six seconds, or even
less, may be sufficient.

In the dull winter months, in the smoky atmosphere of large cities,
or when using an old Collodion brown from free Iodine, multiply these
numbers three or four times, which will be an approximation to the
exposure required. It is by the appearance presented under the influence
of the developer, which will immediately be described, that the operator
ascertains the proper time for exposure to light.

THE DEVELOPMENT OF THE IMAGE.

The details of developing the latent image differ so much in the case of
Positive and Negative pictures, that it is better to describe the two
separately.

The development of direct Positives.--With Sulphate of Iron as a
developer, it is most simple to develope the image by immersion. The
solution may conveniently be poured into a vertical trough, such as that
used for exciting, and the plate immersed by means of a glass dipper in
the usual way. Unless the weather be cold, the image makes its appearance
in three or four seconds, and the film is then immediately washed with
clear water. Whilst in the Bath, the plate is kept in gentle motion, and
the operator must not expect to see the image very distinctly, except
the high lights; the shadows, being faint, are partially concealed by
the unaltered Iodide, but they come out during the fixing. The action
of the Sulphate of Iron is stopped at an early period, or an excess of
development will be incurred. The Bath may be used repeatedly.

In using Pyrogallic Acid or Nitrate of Iron to develope glass Positives,
the plate may be placed upon a levelling-stand, or held in the hand, or by
the pneumatic holder, and the solution poured on quickly at one corner; by
blowing gently or inclining the hand, as the case may be, it is scattered
evenly over the film before the development commences.

If any difficulty is experienced in covering a plate evenly with a strong
developer before the action commences, it may be overcome by using a
shallow cell formed by cementing two or three thicknesses of window-glass
on a piece of patent plate to the depth of a quarter of an inch. The size
of the cell should be only slightly larger than the plate intended to be
developed, that the waste of fluid may be as little as possible.

The cell is held in the left hand, and the plate being placed in it, a
sufficient quantity of the developer is poured on at one corner. By a
slight inclination, the fluid is caused to flow in a uniform sheet over
the surface of the film, backwards and forwards. The image starts out
quickly, and the developer is then at once poured off, and the film washed
as before.

It is very important in developing Positives to use a sufficient quantity
of the solution to cover the plate easily; otherwise oily stains and marks
are formed, from the developer not combining properly with the surface of
the film. For a plate five inches by four, three or four drachms will be
required, and so in proportion for larger sizes.

The appearance of the Positive image after developing, as a guide to
the proper time of exposure.--When the plate has been developed, it is
washed, fixed, and laid upon a dark ground, such as a piece of black
velvet, for inspection.

In the case of a portrait, if the features have an unnaturally black
and gloomy appearance, the dark portions of the drapery, etc., being
invisible, the picture has been _under-exposed_.

On the other hand, in an over-exposed plate, the face is usually pale and
white, and the drapery misty and indistinct. Much however in this respect
depends upon the dress of the sitter (see p. 66), and the manner in which
the light is thrown; if the upper part of the figure is shaded too much,
the face may perhaps be the last to be seen. The operator should accustom
himself to expend pains in the preliminary focussing upon the ground
glass, and to ascertain at that time that every part of the object is
equally illuminated. For this reason, pictures taken in a room are seldom
successful; the light falls entirely upon one side, and hence the shadows
are dark and indistinct.

_The development of Negative Pictures._--This process differs in most
respects from that of Positives. In the latter case, there is a tendency
to over-develope the image; but in the former, to stop the action at too
early a period; hence it is common to find Negative Pictures which are
insufficiently developed, and too pale to print well.

In developing Negatives, many operators place the plate upon a
levelling-stand, and distribute the fluid by blowing gently upon the
surface; others prefer holding it in the hand and pouring the fluid on and
off from a glass measure. The quantity of developer required will be less
than that used for Positives, inasmuch as, if the Acetic Acid be present
in sufficient excess, it is easy to cover the plate before the action
begins. Some Collodion however, especially the glutinous kind, seems to
repel the developer and prevent it from running up to the edge of the
plate. When this is the case, or when oiliness and stains are produced,
from the Bath being old and containing Ether, Alcohol must be added to
the solution of Pyrogallic Acid.

With ordinary Negative Collodion, an addition of Nitrate of Silver to the
developer will often be required; but the Pyrogallic Acid is to be used
alone until the image has reached its maximum of intensity, which it will
do in a minute or so, according to the temperature of the developing room.
The plate may then be examined leisurely by placing it in front of, and
at some distance from, a sheet of white paper. If it is not sufficiently
black, add about four drops of the Nitrate Bath to each drachm of
developer, stir well with a glass rod, and continue the action until the
requisite amount of intensity is obtained. When there is any disposition
in the plate to _fog_ towards the end of the development, it may be
obviated by fixing with Cyanide of Potassium (not Hyposulphite), and then,
after a careful washing, intensifying with Pyrogallic Acid and Nitrate
of Silver in the usual way. The glass which contains the mixture of
Pyrogallic Acid and Nitrate of Silver must be washed out after each plate,
as the black deposit hastens the discoloration of the fresh solution (p.
179).

_Appearance of the Negative image during and after the reducing process,
as a guide to the exposure to light._--An under-exposed plate developes
slowly. By continuing the action of the Pyrogallic Acid, the high lights
_become very black_, but the shadows are invisible, nothing but the yellow
Iodide being seen on those portions of the plate. After treatment with the
Cyanide, the picture shows well as a Positive, but by transmitted light
all the minor details are invisible; the image is black and white, without
any half-tone.

An over-exposed Negative developes rapidly at first, but soon begins
to blacken slightly at every part of the plate. After the fixing is
completed, nothing can often be seen by reflected light but a uniform
grey surface of metallic Silver, without any appearance (or, at most, an
indistinct one) of an image. By transmitted light the plate may appear of
a red or brown colour, and the image is _faint_ and dull. The clear parts
of the Negative being obscured by the fogging, and the half-shadows having
acted so long as nearly to overtake the lights, there is a want of proper
_contrast;_ hence the over-exposed plate is the exact converse of the
under-exposed, where the contrast between lights and shadows is too well
marked, from the absence of intermediate tints.

A Negative which has received the proper amount of exposure,
usually possesses the following characters after the development is
completed:--The image is partially but not fully seen by reflected light.
In the case of a portrait, any dark portions of drapery show well as a
Positive, but the features of the sitter are scarcely to be discerned.
The plate has a general aspect as of fogging _about to commence_, but
not actually established. By transmitted light the figure is bright, and
appears to stand out from the glass: the dark shadows are clear, without
any misty deposit of metallic Silver; the high lights black _almost_ to
complete opacity. The _colour_ of the image however varies much with the
state of the Bath and Collodion and with the brightness of the light.

The remarks already made under the head of Positives, apply equally well
to Negatives; that is, it will be difficult to secure gradation of tone,
unless the object be _equally_ illuminated, without any strong contrast of
light and shade. Hence the direct rays of the sun are, as a rule, to be
avoided, and curtains, etc., employed when practicable.

FIXING AND VARNISHING THE IMAGE.

After the development is completed, and the plate has been carefully
washed by a stream of water, it may be brought out to the light and
treated with the Hyposulphite or Cyanide, until the unaltered Iodide is
entirely cleared off. Some use a Bath for the Cyanide; but it is doubtful
whether much saving is effected by doing so. The plate is again to be
carefully washed after the fixing; and especially if Hyposulphite of
Soda be used. Three or four minutes in running water will not be too
long, or the glass may be left in a dish of water for an hour or two. If
such precautions are neglected, crystals form on drying, and the image is
injured.

Collodion pictures should be protected by a coat of varnish, both
Negatives and Positives having been known to fade when exposed to damp air
without any covering (see p. 166). To prepare transparent varnish. Amber
may be dissolved in Chloroform according to Dr. Diamond's formula;--about
80 grains of amber-beads or pipe-stems should be digested with one ounce
of the Chloroform, and the clear portion separated by filtration. It may
be poured on the plate in the same manner as Collodion, and dries up
speedily into a hard and transparent layer. The Spirit Varnish ordinarily
sold for Negatives requires the aid of heat to prevent the gum from
chilling as it dries; the plate is first warmed gently and the varnish
poured on and off in the usual way; it is then, whilst still dripping,
held to the fire until the Spirit has evaporated. A few trials will render
the operation easy to perform. White Lac dissolved in strong Alcohol or in
Benzole has also been recommended for clear varnish.

Direct Positives are to be varnished, first with a layer of transparent
varnish, and then with black japan. Suggett's patent jet is sometimes
employed, but it has a disagreeable smell, and is apt to crack on drying.
The best black japan used by coachmakers is more elastic and less liable
to crack. Asphalt (4 oz.) dissolved in mineral Naphtha (10 oz.), with
the addition of 30 grains of Caoutchouc dissolved in half an ounce of
the same menstruum, is also said to stand well. A third formula contains
black sealing-wax dissolved in Alcohol. In either case it will be best to
apply first a layer of clear varnish to the film, and afterwards the black
varnish, which should combine with the other without dissolving it.

Positives whitened with Bichloride of Mercury are injured by varnishing;
they must therefore be backed up with black velvet, or Japan laid upon the
opposite side of the glass. Many prefer taking the picture upon coloured
glass, using only a layer of clear varnish; but in this case the Collodion
side being left uppermost, the image is necessarily reversed.

SECTION II.

_Directions for the use of Photographic Lenses._

Those who are comparatively unacquainted with the science of optics
require simple rules to guide them in the choice of a photographic lens,
and in the proper mode of using it.

Two kinds of Achromatic lenses are sold, the Portrait lens and the View
lens; the former of which is constructed to admit a large volume of light,
for the purpose of copying living objects, etc.

A convenient-sized Camera for small portraits is "the half-plate" with a
lens of about 2-1/4 inches diameter, and giving a tolerably flat field on
a surface of 5 inches by 4. Much however in this respect will depend upon
the quality of the glass and also upon its focal length; a short focus
lens taking a picture more quickly, but giving a smaller image, and a
field which is misty towards the edge. There is also a great tendency to
_distortion_ of the image in portrait lenses of large aperture and short
focus, such as those employed for operating in a dull light.

The "whole plate" portrait lens may be expected to cover 6-1/2 by 4-3/4
inches, and has a diameter of about 3-1/4 inches. It will take larger
pictures than the last, but not necessarily in a shorter time; since,
although the aperture for admitting the light is larger, the focal length
is proportionately greater and the light less condensed.

The "quarter-plate" portrait lens of 1-1/4 inch diameter is useful for
stereoscopic subjects and small portraits; which are usually more sharply
defined when taken with a small lens.

The distance at which the Camera is to be placed from the sitter in taking
a portrait, will depend upon the focal length of the lens. The effect of
bringing the Camera nearer is to add to the size of the image, but at the
same time to increase the chance of distortion; hence with every lens of
full aperture, there is a practical limit to the size of picture which can
be taken.

When it is required to obtain a large image with a small lens, a stop
with a central aperture (which may be readily made of a piece of circular
cardboard blackened with Indian ink) must be placed in front of the lens.
This will diminish the amount of light, but will render the picture more
distinct towards the edge, and bring a variety of objects at different
distances into focus at the same time. With a stop attached, the lens may
also be brought nearer to the object without distorting.

With regard to this subject of the distortion often produced by lenses,
observe particularly, that with the portrait combination of full aperture,
and especially when the powers of the glass are rather strained by its
being advanced too near to the sitter,--all objects near to the lens will
be _magnified_, and those more removed will appear diminished; hence, as
the position of the sitter is never quite vertical, the Camera must be
inclined a little _downwards_, or the hands and feet will be enlarged,
the figure in fact becoming pyramidal with the base below; whereas on the
other hand, if the inclination of the Camera be too great, the head and
forehead will be enlarged, and the figure becomes a pyramid with the base
above.

When groups are taken, arrange the objects as near as possible equidistant
from the lens, and use a stop if practicable. Long-focus lenses are the
best for this purpose, allowing the Photograph to be taken further off,
and giving a greater variety of objects in focus at the same time.

Portrait lenses may often be advantageously substituted for View lenses
in copying objects of still life which are _badly lighted_. The aperture
of the lens being large, a Negative can be obtained with an amount of
light which would not suffice if a small stop were used. On the other
hand, if the light be unusually bright, the lens of full aperture is
always the most likely, from its extent of reflecting surface, to produce
a misty and indistinct image. Hence the object should be well backed up
with some neutral colour, or, if that cannot be done, a pasteboard funnel,
projecting about a foot and a half, may be fastened in front of the
lens, in order to exclude rays of light not immediately concerned in the
formation of the image. If the lens were turned towards distant objects
brightly illuminated, and a portion of sky included, there would probably
be diffused light, and consequent fogging of the plate on the application
of the developer. This effect will also invariably follow if the sun's
rays be allowed to fall directly upon the glass.

_Directions for finding the Plane at which the Sharpest Image can be
obtained._--Non-Achromatic Lenses are understood by all to require
correction for the chemical focus; but it is usually said of the compound
glasses, that their two foci correspond. The amateur is recommended, in
order to avoid disappointment, to test the accuracy of this statement, and
also to see that his Camera is constructed with care. To do this, proceed
as follows:--

First ascertain that the prepared sensitive plate falls precisely in
the plane occupied by the ground glass. Suspend a newspaper or a small
engraving at the distance of about three feet from the Camera, and focus
the letters occupying the centre of the field; then insert the slide, with
a square of _ground glass_ substituted for the ordinary plate (the rough
surface of the glass looking inwards), and observe if the letters are
still distinct. In place of the ground glass, a transparent plate with a
square of silver-paper which has been oiled or wetted, may be used, but
the former is preferable.

If the result of this trial seems to show that the Camera is good, proceed
to test the correctness of the Lens.--

Take a Positive Photograph with the full aperture of the portrait Lens,
the central letters of the newspaper being carefully focussed as before.
Then examine at what part of the plate the greatest amount of distinctness
of outline is to be found. It will sometimes happen, that whereas the
exact centre was focussed visually, the letters on a spot midway between
the centre and edge are the sharpest in the Photograph. In that case the
chemical focus is longer than the other, and by a distance equivalent to,
but in the opposite direction of, the space which the ground glass has to
be moved, in order to define those particular letters sharply to the eye.

When the chemical focus is the shorter of the two, the letters in the
Photograph are indistinct at every portion of the plate; the experiment
must therefore be repeated, the lens being shifted an eighth of an inch
or less. Indeed it will be proper to take many Photographs at minute
variations of focal distance before the capabilities of the lens will be
fully shown.

The object of finding the point at which the sharpest image is obtained
will also be assisted by placing several small figures in different planes
and focussing those in the centre. This being done, if the more distant
figures come out distinctly in the Photograph, the chemical focus is
_longer_ than the Visual, or _vice versâ_ when the nearest ones are most
sharply defined.

_The Single Achromatic Lens._--A useful lens for landscape Photography
is one of about 3 inches diameter and 15 inches focal length, which may
be expected to cover a field of 10 inches by 8. With the lens, stops are
supplied of various diameters, the largest of which will be useful in dull
weather; the smaller when the field is required to be rendered sharp to
the very edge.

The stop is arranged at a certain distance in front of the lens, and must
not be moved. If it were brought close up to the glass, the field would
not be so flat; the effect being then the same as that of a stop placed in
front of a Portrait Lens, viz. simply to cut off the outside portion of
the glass.[38]

[38] See this subject explained in 'Photographic Journal,' vol. ii. p. 133.

In taking Photographs of architectural and other subjects with vertical
outlines, it is very important to have the Camera placed perfectly
horizontal; since, if it be inclined either upwards or downwards, the
perpendiculars will be destroyed and the object will appear of a pyramidal
form, falling inwards or outwards, as before shown. It is convenient to
rule the ground focussing glass with a number of parallel lines in both
directions, which enables the operator at once to see that the position of
the instrument is correct.

SECTION III.

_Mode of copying Engravings, Etchings, etc._

The engraving to be Photographed should be removed from its frame (the
glass causing irregular reflection) and suspended vertically and in a
reversed position, in a good diffused light. A black cloth may be placed
behind the picture with advantage if any surface likely to reflect light
be presented to the lens.

The Camera must be fixed immovably, so as not to vibrate in the least
degree when the cap of the lens is taken off. It should be pointed at
right angles to the picture, and the focus determined in the ordinary
way. Either a portrait or a single lens may be used, with a diaphragm
sufficiently small to render the image distinct up to the edge.

It is not desirable to employ too thin a Collodion, since perfect opacity
of the darkest parts of the Negative is essential. An old Collodion
containing free Iodine is better than a contractile Collodion, as giving
a more intense and clear image. Pure Collodion iodized with Iodide of
Cadmium, if found wanting in intensity, may be at once rendered fit for
use in copying engravings by adding Glycyrrhizine (p. 209), until the dark
parts of the negative become very opaque, and subsequently softening the
excessive hardness, if necessary, by dropping alcoholic solution of Iodine
into the Collodion until it reaches a straw-yellow tint. A second formula
useful in iodizing Collodion for a similar purpose is as follows.

  Iodide of Potassium                4 grains.
  Bromide of Potassium               1 grain.

This, with addition of Glycyrrhizine, will give a very black image.

Etchings, diagrams, and drawings with pencil or ink, without much
middle-tint, if on thin paper, are easily copied without the aid of the
Camera, by simply laying the sketch upon a sheet of Negative Paper,
exposing for a brief time to the light, and developing with Gallic Acid.
This yields a Negative which is employed for printing Positives in the
usual way. Full directions on this subject will be found in the Second
Section of the following Chapter.

A more simple plan, and one which will succeed when great delicacy is not
required, consists in laying the sketch upon a sheet of Positive printing
paper (a highly salted paper will be the best, as giving most intensity)
and exposing to the light until a copy is obtained. All the details are
faithfully rendered in this way, but it is sometimes difficult to obtain a
Negative sufficiently black to yield a _vigorous_ print.

SECTION IV.

_Rules for taking Stereoscopic Photographs._

Binocular pictures of a large size, for the reflecting Stereoscope, may
be taken with an ordinary View lens of about 15 inches focus. The ground
glass of the Camera having been ruled with cross lines in the manner
described at page 231, the position of some prominent object is marked
upon one of the lines with a pencil, and the first view is taken. The
stand is then moved laterally to the proper distance, and the Camera
adjusted to its second position by shifting it until the marked object
occupies the same place as before. The distance between the two positions
should be about one foot when the foreground of the picture is twenty-five
feet from the instrument, or four feet when it is at thirty or forty
yards. But, as before shown at page 71, this rule is not to be followed
implicitly, much depending upon the character of the picture and the
effect desired.

Photographs for the lenticular Stereoscope are taken with small lenses
of about 4-1/2 inches focus. For portraits, a Camera may advantageously
be fitted with two double-combination lenses, of 1-3/4 inches diameter,
exactly equal in focal length and in rapidity of action. The caps are
removed simultaneously, and the pictures impressed at the same instant.
The centres of the lenses may be separated by three inches when the Camera
is placed at about six feet from the sitter, or four inches when the
distance is increased to eight feet.

Pictures taken with a binocular Camera of this kind, require to be mounted
in a reversed position to that which they occupy on the glass: for since
the image of the Camera is _inverted_, when it is turned round and made
erect, the right-hand picture will necessarily stand on the left side, and
_vice versâ_.

Mr. Latimer Clark has devised an arrangement for taking stereoscopic
pictures with a single Camera, which is exceedingly ingenious. Its most
important feature is a contrivance for rapidly moving the Camera in a
lateral direction without disturbing the position of the image upon the
ground glass. This will be understood by a reference to the following
woodcut.

"A strongly-framed Camera-stand carries a flat table, about 20 inches wide
by 16, furnished with the usual adjustments. Upon this are laid two flat
bars of wood in the direction of the object, and parallel, and about the
width of the Camera asunder. They are 18 inches in length; their front
ends carry stout pins, which descend into the table and form centres
upon which they turn. Their opposite ends also carry similar pins, but
these are directed upwards, and fit into two corresponding holes in the
tail-board of the Camera.

"Now when the Camera is placed upon these pins, and moved to and fro
laterally, the whole system exactly resembles the common parallel ruler.
The two bars form the guides, and the Camera, although capable of free
lateral motion, always maintains a parallel position. In this condition
of things it is only suited to take stereoscopic pictures of an object
at an infinite distance; but to make it move in an arc, _converging_ on
an object at any nearer distance, it is only necessary to make the two
guide-bars approximate at their nearer end so as to converge slightly
towards the object; and by a few trials some degree of convergence will
be readily found at which the image will remain as it were _fixed_ on the
focussing glass while the Camera is moved to and fro. To admit of this
adjustment, one of the pins descends through a Slot in the table and
carries a clamping-screw, by means of which it is readily fixed in any
required position.

"In order however to render the motion of the Camera smoother, it is
advisable not to place it directly upon the two guides, but to interpose
two thin slips of wood, lying across them at right angles, beneath the
front and back of the Camera respectively (and which may be fixed to the
Camera if preferred), and to dust the surfaces with powdered soap-stone or
French chalk."

In addition to this arrangement for moving the Camera laterally, the
_slide_ for holding the sensitive plates must be modified from the common
form. It is oblong in shape, and being about ten or eleven inches long,
requires some little adaptation to fit it to the end of an ordinary
Camera. The glasses are cut to about 6-3/4 inches by 3-1/4; and when
coated with Iodide of Silver, the two images are impressed side by side,
the plate being shifted laterally about 2-1/2 inches, at the same time and
in the same direction as the Camera itself.

The operation of taking a portrait is thus performed. The focus having
been adjusted for both positions, and the Camera and the slide both drawn
to the left-hand, the door is raised and the plate exposed; the Camera and
the slide are then shifted to the right-hand, and the plate in its new
position having been again exposed, the door is closed and the operation
completed.[39]

[39] See 'Photographic Journal,' vol. i. page 59.

Pictures taken with this instrument do not require to be reversed in
mounting, the left picture being purposely formed on the right-hand side
of the glass.

SECTION V.

_On the Photographic delineation of Microscopic objects._

Many specimens of Micro-photography which have been exhibited are
exceedingly elaborate and beautiful; and their production is not
difficult to one thoroughly acquainted with the use of the Microscope and
with the manipulations of the Collodion Process. It is important however
to possess a good apparatus, and to have it properly arranged.

The object-glass of the ordinary compound Microscope is the only part
actually required in Photography, but it is useful to retain the _body_
for the sake of the adjustments, and the mirrors used in the illumination.
The _eye-piece_ however, which simply magnifies the image formed by the
object-glass, is not necessary, since the same effect of enlargement may
be obtained by lengthening out the dark chamber, and throwing the image
further off.

_Arrangement of the Apparatus._--The Microscope is placed with its body
in a horizontal position, and the eye-piece being removed, a tube of
paper, properly blackened in the interior, or lined with black velvet, is
inserted into the instrument, to prevent irregular reflection of light
from the sides.

A dark chamber of about two feet in length, having at one end an aperture
for the insertion of the eye-piece end of the body, and at the other a
groove for carrying the slide containing the sensitive plate, is then
attached; care being taken to stop all crevices likely to admit diffused
light. An ordinary Camera may be employed as the dark chamber, the lens
being removed, and the body lengthened out if required by a conical tube
of gutta-percha, made to fasten into the flange of the lens in front. The
whole apparatus should be placed exactly in a straight line, that the
ground glass used in focussing may fall at right angles to the axis of the
Microscope.

The length of the chamber, measuring from the object-glass, may be from
two to three feet, according to the size of image required; but if
extended beyond this, the pencil of light transmitted by the object-glass
is diffused over too large a surface, and a faint and unsatisfactory
picture is the result. The object should be illuminated by sunlight if
it can be obtained, but a bright diffused daylight will succeed with
low-power glasses, and especially when Positives are taken. Employ the
concave mirror for reflecting the light on the object in the latter case;
but in the former the _plane mirror_ is the best, except with powers
exceeding a quarter of an inch, and of large angular aperture.

The image upon the ground glass should appear bright and distinct, and the
field of a circular form and evenly illuminated; when this is the case,
all is ready for inserting the sensitive plate.

The time of exposure must be varied according to the intensity of the
light, the sensibility of the Collodion, and the degree of magnifying
power; a few seconds to a minute will be about the extremes; but minute
directions are not required, as the operator, if a good Photographer, will
easily ascertain the proper time for exposing (see page 224).

At this point a difficulty will probably occur from the plane of the
chemical focus not corresponding, as a rule, with that of the visual
focus. This arises from the fact that the object-glasses of Microscopes
are "over-corrected" for colour, in order to compensate for a little
chromatic aberration in the eye-piece. The violet rays, in consequence
of the over-correction, are projected _beyond_ the yellow, and hence the
focus of chemical action is further from the glass than the visible image.

The allowance may be made by shifting the sensitive plate, or, what
amounts to the same thing, by removing the object-glass a little _away_
from the object with the fine adjustment screw; the latter is the most
convenient. The exact distance must be determined by careful experiment
for each glass; but it is greatest with the low powers, and decreases as
they ascend.

Mr. Shadbolt gives the following as a guide:--"An inch and a half
objective of Smith and Beck's make required to be shifted 1/50th of an
inch, or two turns of _their_ fine adjustment; a 2/3rds of an inch,
1/200th of an inch, or half a turn; and a 4/10ths of an inch, 1/1000th
of an inch, or about two divisions of the adjustment. With the 1/4th
and higher powers, the difference between the foci was so small as to be
practically unimportant."

There is also reason to think that the _kind of light_ employed has an
influence upon the separation of the foci. Mr. Delves finds that with
sunlight the difference between them is very small even with the low
powers, and inappreciable with the higher; whereas in using diffused
daylight which has undergone a previous reflection from white clouds, it
is considerable.

The object-glasses of the same maker, and particularly those of different
makers, also vary much; so that it will be necessary to test each glass
separately, and to register the allowance which is required.

Having found the chemical focus, the principal difficulty has been
overcome, and the remaining steps are the same in every respect as for
ordinary Collodion Photographs.

To those who cannot devote their time to Photography during the day,
Mr. Shadbolt's observations on the use of artificial light may be of
service. He employs _Camphine_, which gives a whiter flame than gas, or a
moderator lamp; placing the source of light in the focus of a plano-convex
lens of 2-1/2 to 3 inches diameter (the flat side towards the lamp), and
condensing the parallel rays so obtained on the object, by a second lens
of about 1-1/2-inch diameter and 3-inch focus.

This mode of illumination, being feeble in chemical rays, is best adapted
for object-glasses of low power. The exposure required to produce a
Negative impression with the one-inch glass may be from three to five
minutes. As the sensitive plate would be liable to become dry during that
time, it is recommended to coat it with some preservative solution by the
modes described in the sixth Chapter. Mr. Crookes having lately shown that
the Bromide of Silver is more sensitive than the Iodide to artificial
light, a mixture of the two salts may conveniently be used (see pp. 66 and
232).

The development may be conducted in the same manner as that for preserved
sensitive plates; fixing with Cyanide of Potassium before the development
is fully complete, if any tendency to fogging is observed (see page 224).

The Rev. W. Towler Kingsley has communicated a process by which very
beautiful Microscopic Photographs have been obtained. He illuminates (in
the absence of sunlight) with the brilliant light produced by throwing
a jet of mixed Oxygen and Hydrogen gases upon a small cone of Lime
or Magnesia. Particular stress is laid upon the object-glass of the
Microscope being a good one for the purpose; and indeed all who have given
attention to the subject are agreed upon this point--that there is a
considerable difference in the Photographic value of objectives, and this
independent of the angular aperture of the glass.

CHAPTER IV.

THE PRACTICAL DETAILS OF PHOTOGRAPHIC PRINTING.

This Chapter is divided as follows:--

  Section I.--The ordinary direct process of positive printing.
  Section II.--Positive printing by development.
  Section III.--The mode of toning Positives by Sel d'or.
  Section IV.--On printing enlarged or reduced Positives,
    transparencies, etc.

SECTION I.

_Positive Printing by the direct action of Light._

This includes--the preparation of sensitive paper,--of fixing and toning
Baths,--and the manipulatory details of the process.

_Selection of Paper for Photographic Printing._--The ordinary varieties
of paper sold in commerce are not well adapted for the production of
Positive prints. Papers are manufactured purposely which are more smooth
and uniform in texture. Many samples of even the finest paper are however
defective, and hence each sheet should be examined separately by holding
it against the light, and if spots or irregularities of texture are seen,
it should be rejected. These spots usually consist of small particles of
brass or iron, which, when the paper is rendered sensitive, decompose the
Nitrate of Silver and leave a circular mark very noticeable after fixing.

The foreign papers, French and German, are different from the English.
They are porous and sized with starch, the English being sized with
gelatinous animal matter. In all cases there is a difference in smoothness
between the two sides of the paper, which may be detected by holding each
sheet in such a manner that the light strikes it at an angle; the wrong
side is that on which dark wavy bands, of an inch to an inch and a half
in breadth, are seen, caused by the strips of felt on which the paper
was dried. With most qualities of paper no difficulty whatever will be
experienced in detecting the broad and regular bands above referred to;
but when they cannot be seen, the wrong side of the sheet may be known
by wire markings crossing each other, or if the paper be wetted at the
corner, one side may appear evidently smoother than the other.

PREPARATION OF SENSITIVE PAPER.

There are three principal varieties of sensitive paper in common use, viz.
the Albuminized, the plain, and the Ammonio-Nitrate paper.

Formula I. _Preparation of Albuminized Paper._--This includes the salting
and albuminizing, and the sensitizing with Nitrate of Silver.

_The Salting and Albuminizing._--Take of

  Chloride of Ammonium, or Pure
    Chloride of Sodium                   200 grains.
  Water                                   10 fluid ounces.
  Albumen                                 10 fluid ounces.

If distilled water cannot be procured, rain water or even common spring
water[40] will answer the purpose. To obtain the Albumen, use new-laid
eggs, and be careful that in opening the shell the yolk is not broken;
each egg will yield about one fluid ounce of Albumen.

[40] If the water contained much Sulphate of Lime, it is likely that the
sensitiveness of the paper would be impaired (?).

When the ingredients are mixed, take a bundle of quills or a fork, and
beat the whole into a perfect froth. As the froth forms, it is to be
skimmed off and placed in a flat dish to subside. The success of the
operation depends entirely upon the manner in which this part of the
process is conducted;--if the Albumen be not thoroughly beaten, flakes of
animal membrane will be left in the liquid, and will cause streaks upon
the paper. When the froth has partially subsided, transfer it to a tall
and narrow jar, and allow to stand for several hours, that the membranous
shreds may settle to the bottom. Then pour off the upper clear portion,
which is fit for use. Albuminous liquids are too glutinous to run well
through a paper filter, and are better cleared by subsidence.

A more simple plan than the above, and one equally efficacious, is to
fill a bottle to about three parts with the salted mixture of Albumen and
water, and to shake it well for ten minutes or a quarter of an hour until
it loses its glutinosity and can be poured out smoothly from the neck of
the bottle. It is then to be transferred to an open jar, and allowed to
settle as before.

The solution prepared by the above directions will contain exactly ten
grains of salt to the ounce, dissolved in an equal bulk of Albumen and
water. Some operators employ the Albumen alone without an addition of
water; but this commonly gives a highly varnished appearance, which is
thought by most to be objectionable. Much however will depend upon the
kind of paper which is employed, certain varieties taking more gloss than
others; Papier Rive, for instance, often requires the Albumen to be nearly
or quite undiluted.

The principal difficulty in Albuminizing paper, is to avoid the occurrence
of _streaky lines_, which, when the paper is rendered sensitive, _bronze_
strongly under the influence of the light. To avoid them, use the eggs
quite fresh, and lower the paper on to the liquid by one steady movement;
if a pause be made, a line will probably be formed. Some papers are not
readily wetted by the Albumen, and when such is the case, a few drops of
spirituous solution of bile, or a fragment of the prepared Ox-Gall sold
by the artists' colour-men, will be found a useful adjunct. Care must be
taken however not to add an excess, or the Albumen will be rendered too
fluid, and will sink into the paper, leaving no gloss.

In salting and albuminizing Photographic paper by the formula above given,
it is found that each quarter-sheet, measuring eleven inches by nine
inches, removes one fluid drachm and a half from the bath, equivalent
to about one grain and three-quarters of salt (including droppings). In
salting plain paper, each quarter-sheet takes up only one drachm; so that
the glutinous nature of the Albumen causes a third part more of salt to be
retained by the paper.

English papers are not good for albuminizing; they do not take the Albumen
properly, and curl up when laid upon the liquid: the process of toning the
prints is also slow and tedious. The thin negative paper of Canson, the
Papier Rive, and Papier Saxe, have succeeded with the writer better than
Canson's Positive paper, which is often recommended; they have a finer
texture, and give more smoothness of grain.

To apply the Albumen, pour a portion of the solution into a flat dish to
the depth of half an inch. Then, having previously cut the paper to the
proper size, take a sheet by the two corners, bend it into a curved form,
convexity downwards, and lay it upon the Albumen, the centre part first
touching the liquid, and the corners being lowered gradually. In this way
all bubbles of air wall be pushed forwards and excluded. One side only of
the paper is wetted: the other remains dry. Allow the sheet to rest upon
the solution for _one minute and a half_, and then raise it off, and pin
it up by two corners. If any circular spots, free from Albumen, are seen,
caused by bubbles of air, replace the sheet for the same length of time as
at first.

The paper must not be allowed to remain upon the salting Bath much longer
than the time specified, because the solution of Albumen being _alkaline_
(as is shown by the strong smell of Ammonia evolved on the addition of the
Chloride of Ammonium) tends to remove the size from the paper and to sink
in too deeply; thus losing its surface gloss.

Albuminized paper will keep a long time in a dry place. Some have
recommended to press it with a heated iron, in order to coagulate the
layer of Albumen upon the surface; but this precaution is unnecessary,
since the coagulation is perfectly effected by the Nitrate of Silver used
in the sensitizing; and it is doubtful whether a layer of _dry_ Albumen
would admit of coagulation by the simple application of a heated iron.

_To render the paper sensitive._--This operation must be conducted by the
light of a candle, or by yellow light. Take of

  Fused Nitrate of Silver                 60  grains.
  Glacial Acetic Acid                     1/3 minim.
  Distilled Water                          1  ounce.

Prepare a sufficient quantity of this solution, and lay the sheet upon it
in the same manner as before. Three minutes' contact will be sufficient
with the thin Negative paper, but if the Canson Positive paper be used,
four or five minutes must be allowed for the decomposition. The papers
are raised from the solution by a pair of bone forceps or common tweezers
tipped with sealing-wax; or a pin may be used to lift up the corner, which
is then taken by the finger and thumb and allowed _to drain a little_
before again putting in the pin, otherwise a white mark will be produced
upon the paper, from decomposition of the Nitrate of Silver. When the
sheet is hung up, a small strip of blotting-paper suspended from the
lower edge of the paper will serve to drain off the last drop of liquid.

A Bath prepared by the above formula is stronger than is really necessary.
Forty grains of Nitrate to the ounce of water is abundantly sufficient if
the sample be pure; but it must be borne in mind that the _strength_ of
the Bath diminishes _rapidly_ by use, and hence, when the prints begin to
be wanting in vigour, with pale shadows and perhaps a spotted appearance,
an addition of Nitrate of Silver must be made. Fused Nitrate of Silver
is recommended in preference to the crystallized Nitrate, on account of
the latter being occasionally contaminated with an impurity alluded to at
page 101. This when present will be likely to redden the pictures and to
interfere with the rapidity of bronzing.

The solution of Nitrate of Silver becomes after a time discoloured by the
Albumen, but may be used for sensitizing until it is nearly black. The
colour can be removed by Animal Charcoal,[41] but a better plan is to use
the "kaolin," or pure white china clay. This substance often contains
Carbonate of Lime, and effervesces with acids: it must in such a case be
purified by washing in vinegar, or the Bath will become alkaline, and
dissolve off the Albumen. It has been stated that an addition of Alcohol
to the Nitrate Bath prevents it discolouring with Albumen.

[41] Common Animal Charcoal contains Carbonate and Phosphate of Lime, the
former of which renders the Nitrate of Silver alkaline; purified Animal
Charcoal is usually acid from Hydrochloric Acid.

Sensitive albuminized paper will usually keep for several days, if
protected from the light, but afterwards turns yellow from partial
decomposition.

Formula II. _Preparation of plain paper._--Take of

  Chloride of Ammonium or Sodium         160 grains.
  Purified Gelatine                       20 grains.
  Iceland Moss[42]                         60 grains.
  Water                                   20 ounces.

[42] Iceland Moss is recommended because the writer finds that Positives
so printed stand the action of destructive tests better than prints on
plain paper, and equal to prints upon Ammonio-Nitrate paper.

Pour boiling water upon the Moss and Gelatine and stir until the latter is
dissolved, then cover the vessel and set aside until cold; add the salt,
and strain.

Use Papier Saxe or Towgood's paper,[43] floated upon the salting Bath in
the same manner as directed for Albumen at p. 243.

[43] The writer does not recommend the Positive paper of De Canson,
having noticed that prints upon that paper do not withstand the action of
sulphuretting agents so well as others (?).

Render sensitive by floating for two or three minutes upon a solution of
Nitrate of Silver, 40 grains to the ounce. Thirty grains to the ounce,
or less, will be sufficient if the sample be pure; but in that case
occasional additions of fresh Nitrate of Silver must be made, as the Bath
loses strength.

_A second Formula for plain paper._--Take of

  Chloride of Ammonium                 200 grains.
  Citrate of Soda[44]                  200   "
  Gelatine                              20   "
  Water                                 20 fluid ounces.

[44] This salt may be obtained at the operative chemists; or it may be
prepared extemporaneously by neutralizing 112 grains of pure Citric Acid,
free from Tartaric Acid, with 133 grains of the dried Bicarbonate or
"Sesquicarbonate" of Soda, used for effervescing draughts.

If Towgood's or any English paper be used, the Citric Acid, Carbonate of
Soda, and Gelatine may be omitted. With a foreign paper the Citrate tends
to give a purple tone to the Positive, when toned by Sel d'or, but the
gold toning Bath must be in active order, or the prints will be too red.
The Citric Acid also should not be in excess over the alkaline Carbonate.

Render sensitive by floating for three minutes upon a Nitrate Bath of
sixty grains to the ounce of water.

Formula III. _Ammonio-Nitrate Paper._--This is always prepared without
Albumen, which is dissolved by Ammonio-Nitrate of Silver. Take of

  Chloride of Ammonium                 100 grains.
  Citrate of Soda                      200   "
  Gelatine                              20   "
  Water                                 20 fluid ounces.

Dissolve the Gelatine by the aid of heat; add the other ingredients, and
filter. The solution cannot be kept longer than two or three weeks without
becoming mouldy. The Saxony paper, or Towgood's English paper, may be
employed; the Gelatine and Citrate being retained or omitted, according to
the taste of the operator and the mode of toning which is adopted.

Render sensitive by a solution of Ammonio-Nitrate of Silver, 60 grains to
the ounce of water, which is prepared as follows:--

Dissolve the Nitrate of Silver in one-half of the total quantity of water.
Then take a pure solution of Ammonia and drop it in carefully, stirring
meanwhile with a glass rod. A brown precipitate of Oxide of Silver first
forms, but on the addition of more Ammonia it is re-dissolved.[45] When
the liquid appears to be clearing up, add the Ammonia very cautiously, so
as not to incur an excess. In order still further to secure the absence
of free Ammonia, it is usual to direct, that when the liquid becomes
perfectly clear, a drop or two of solution of Nitrate of Silver should be
added until a _slight turbidity_ is again produced. Lastly, dilute with
water to the proper bulk. If the crystals of Nitrate of Silver employed
contain a large excess of free Nitric Acid, no precipitate will be formed
on the first addition of Ammonia. The free Nitric Acid, producing _Nitrate
of Ammonia_ with the alkali, keeps the Oxide of Silver in solution. This
cause of error however is not likely to happen frequently, since the
amount of Nitrate of Ammonia required to prevent all precipitation would
be considerable. From the same reason, viz. the presence of Nitrate of
Ammonia, it is often useless to attempt to convert an old Nitrate Bath
already used for sensitizing, into Ammonio-Nitrate.

[45] If the excess of Ammonia does not readily dissolve it, probably the
Nitrate of Silver is impure.

Ammonio-Nitrate of Silver should be kept in a dark place, being more prone
to reduction than the Nitrate of Silver.

Sensitizing paper with Ammonio-Nitrate.--It is not usual to float the
paper when, the Ammonio-Nitrate of Silver is used. If a bath of this
liquid were employed, it would not only become quickly discoloured by
the action of organic matter dissolved out of the papers, but would soon
contain abundance of free Ammonia (see the Vocabulary, Part III., art.
"Ammonio-Nitrate"); and an excess of Ammonia in the liquid produces an
injurious effect by dissolving away the sensitive Chloride of Silver.

The Ammonio-Nitrate is therefore applied with a glass rod, or by brushing,
and in neither case is any of the liquid which has once touched the paper
allowed to return into the bottle.

Brushes are manufactured purposely for applying Silver solutions, but the
hair is soon destroyed unless the brush be kept scrupulously clean. Lay
the salted sheet upon blotting-paper, and wet it thoroughly by drawing
the brush first lengthways and then across. Allow it to remain flat for
a minute or so, in order that a sufficient quantity of the solution may
be absorbed (you will see when it is evenly wet by looking along the
surface), and then pin up by the corner in the usual way. If, on drying,
white lines appear at the points last touched by the brush, it is probable
that the Ammonio-Nitrate contains free Ammonia.

The employment of a glass rod is a very simple and economical mode of
applying Silver solutions. Procure a flat piece of board somewhat smaller
than the sheet to be operated on, and having turned over the edges of the
paper, secure them with a pin. Next bring the board near to the corner
of the table, and laying the glass rod along the edge of the paper,
allow the fluid to drop into the groove so formed; then carry the rod
directly across the sheet, when an even wave of fluid will be spread over
the surface. A pipette made of glass tubing, when dipped into the bottle
and the upper end closed with the finger, will withdraw as much of the
Ammonio-Nitrate as is required; and if a scratch be made upon the tube at
a point corresponding to 30 or 40 minims, it will be found sufficient for
a quarter sheet of the Papier Saxe.

Ammonio-Nitrate paper, however prepared, cannot be kept many hours without
becoming brown and discoloured.

_Use of a solution of Oxide of Silver in Nitrate of Ammonia._--The great
objection to the use of Ammonio-Nitrate of Silver is the _decomposition_
which it sometimes experiences by keeping, metallic Silver separating
and Ammonia being set free. To obviate this liberation of Ammonia, the
Author employs Nitrate of Ammonia as the solvent for the Oxide of Silver.
The solution is prepared as follows:--Dissolve 60 grains of _Nitrate
of Silver_ in half an ounce of water, and drop in Ammonia until the
precipitated Oxide of Silver is exactly re-dissolved. Then divide this
solution of Ammonio-Nitrate of Silver into two equal parts, to one of
which add Nitric Acid cautiously, until a piece of immersed litmus-paper
is reddened by an excess of the acid; then mix the two together, fill up
to one ounce with water, and filter from the milky deposit of Chloride or
Carbonate of Silver, if any be formed.

This solution of Oxide of Silver in Nitrate of Ammonia appears to possess
all the advantages of the Ammonio-Nitrate without the inconvenience of
liberating so much free Ammonia upon the surface of the sensitive sheets.

_Hints in selecting from the above Formulæ._--Albuminized paper is the
most simple and generally useful; it is well fitted for small portraits
and stereoscopic Photographs. The Ammonio-Nitrate Process requires more
experience, but gives excellent results when black tones are required: it
may be used for larger portraits, engravings, etc.

Plain paper rendered sensitive by floating upon a Bath of Nitrate of
Silver is easier of manipulation than the Ammonio-Nitrate, and will be
found to be better adapted for toning by the Sel d'or Bath (p. 267) than
the Albuminized Paper.

PREPARATION OF THE FIXING AND TONING BATH.

Take of

  Chloride of Gold                         4 grains.
  Nitrate of Silver                       16 grains.
  Hyposulphite of Soda[46]                  4 ounces.
  Water                                    8 fluid ounces.

[46] The common kind of Hyposulphite of Soda occurring in yellow and
discoloured masses, is too impure for use in Photography, and requires
re-crystallization.

Dissolve the Hyposulphite of Soda in four ounces of the water, the
Chloride of Gold in three ounces, the Nitrate of Silver in the remaining
ounce; then pour the diluted Chloride by degrees into the Hyposulphite,
stirring with a glass rod; and afterwards the Nitrate of Silver in the
same way. This order of mixing the solutions is to be strictly observed:
if it were reversed, the Hyposulphite of Soda being added to the Chloride
of Gold, the result would be the reduction of Metallic Gold; Hyposulphite
of Gold, which is formed, being an unstable substance, and not capable
of existing in contact with unaltered Chloride of Gold. If however it be
dissolved by Hyposulphite of Soda immediately on its formation, it is
rendered more permanent, by conversion into a double salt of Soda and Gold.

In place of Nitrate of Silver, recommended in the formula, Chloride of
Silver may be used, but not Iodide of Silver, as the formation of Iodide
of Sodium would be objectionable (p. 136). For the same reason it is
better not to add any part of the Hyposulphite Bath used for fixing
Negatives, to the Positive colouring solution.

This toning Bath is not to be employed immediately after mixing,
but should be set aside until a portion of Sulphur (produced by
free Hydrochloric Acid, and Tetrathionate of Soda reacting upon the
Hyposulphite) has subsided. It will be very active at the expiration of a
few days or a week; but upon keeping for a longer time, loses much of its
efficacy by a process of spontaneous change.

The immersion of prints also lessens the quantity of Gold; and hence,
when the Bath begins to work slowly, more of the Chloride must be added,
the Sulphur being allowed to deposit as before. Filtration through
blotting-paper will not be required.

The writer finds that after a certain time, when the Bath has been long
used, and organic matters, Albumen, etc., have accumulated in it, it is
better, and more economical, to throw away what remains, and to prepare
a new solution. The addition of Chloride of Gold to an old Bath will not
always make it work as quickly as one recently mixed.

THE MANIPULATORY DETAILS OF PHOTOGRAPHIC PRINTING.

These include--the exposure to light, or printing properly so called; the
fixing and toning; and the washing, drying, and mounting of the proof.

The Exposure to Light.--For this purpose reversing frames are sold, which
admit of being opened at the back, in order to examine the progress of the
darkening by light, without producing any disturbance of position.

Simple squares of glass however succeed equally well, when a little
experience has been acquired. They may be held together by the wooden
clips sold at the American warehouses at one shilling per dozen. The lower
plate should be covered with black cloth or velvet.

Supposing the frame to be employed, the shutter at the back is removed,
and the Negative laid flat upon the glass, Collodion side uppermost. A
sheet of sensitive paper is then placed upon the Negative, sensitive side
downwards, and the whole tightly compressed by replacing and bolting down
the shutter.

This operation may be conducted in the dark room; but unless the light be
strong, such a precaution will not be required. The time of exposure to
light varies much with the density of the Negative and the power of the
actinic rays, as influenced by the season of the year and other obvious
considerations. As a general rule, the best Negatives print slowly;
whereas Negatives which have been under-exposed and under-developed print
more quickly.

In the early spring or summer, when the light is powerful, probably about
ten to fifteen minutes will be required; but from three-quarters of an
hour to an hour and a half may be allowed in the winter months, even in
the direct rays of the sun.

It is always easy to judge of the length of time which will be sufficient,
by exposing a small slip of the sensitive paper, unshielded, to the sun's
rays, and observing how long it takes to reach the coppery stage of
reduction. Whatever that time may be, nearly the same will be occupied in
the printing, if the Negative be a good one.

When the darkening of the paper appears to have proceeded to a
considerable extent, the frame is to be taken in and the picture examined.
If squares of plate glass are used to keep the Negative and sensitive
paper in contact, some difficulty may be experienced at first in returning
it precisely to its former position after the examination is complete,
but this will easily be overcome by practice. The finger and thumb should
be fixed on the lower corners or edge, and the plate raised evenly and
quickly.

If the exposure to light has been sufficiently long, the print appears
slightly darker than it is intended to remain. The toning Bath dissolves
away the lighter shades, and reduces the intensity, for which allowance is
made in the exposure to light. A little experience soon teaches what is
the proper point; but much will depend upon the state of the toning Bath;
and albuminized paper will require to be printed somewhat more deeply than
plain paper.

If, on removal from the printing-frame, a peculiar _spotted_ appearance is
seen, produced by unequal darkening of the Chloride of Silver, either the
Nitrate Bath is too weak, the sheet removed from its surface too speedily,
or the paper is of inferior quality.

On the other hand, if the general aspect of the print is a rich
chocolate-brown in the case of Albumen, a dark slate-blue with
Ammonio-Nitrate Paper, or a reddish purple with paper prepared with
Chloride and Citrate of Silver, probably the subsequent parts of the
process will proceed well.

If, in the exposure to light, the shadows of the proof become very
decidedly _coppery_ before the lights are sufficiently printed, the
Negative is in fault. Ammonio-Nitrate paper highly salted is particularly
liable to this fault of excess of reduction, and especially so if the
light be powerful; hence it is best, in the summer months, not to print
by the direct rays of the Sun. This point is important also, because the
excessive heat of the Sun's rays often cracks the glasses by unequal
expansion, and glues the Negative firmly down to the sensitive paper. An
exception however may be made in the case of Negatives of great intensity;
which are printed most successfully upon, a weakly sensitized paper
(p. 124) exposed to the full rays of the Sun; a feeble light not fully
penetrating the dark parts.

_The fixing and toning of the proof._--No injury results from postponing
this part of the process for many hours, provided the print be kept in a
dark place.

The mode often followed is to immerse the Positive in the Hyposulphite
Bath in the state in which it comes from the printing-frame; moving it
about in the liquid in order to displace air-bubbles, which, if allowed
to remain, produce spots. But the Author, for reasons given in the first
part of the Work (pp. 129 and 165), recommends that the print should
first be washed in common water until the soluble Nitrate of Silver has
been removed.[47] This is known to be the case when the liquid flows
away clear; the first milkiness being caused by the soluble Carbonates
and Chlorides in the water precipitating the Nitrate of Silver. Greater
security is thus afforded that the print will be toned in a really
permanent manner, since after removing the Nitrate of Silver from the
proof, the Bath does not work quickly unless the supply of Gold be well
maintained.

[47] This water must be free from Hyposulphite of Soda, or the print will
become discoloured.

Immediately on coming in contact with the Hyposulphite of Soda in the
fixing and toning Bath, the chocolate brown or violet tint of the Positive
disappears, and leaves the image of a red tone. Albumen proofs become
brick-red; Ammonio-Nitrate a sepia or brown-black. If the colour is
unusually _pale_ at this stage, probably the Silver Bath is too weak, or
the quantity of Chloride of Ammonium or Sodium insufficient.

After the print has been thoroughly reddened, the _toning_ action begins,
and must be continued until the desired effect is obtained. This may
happen in from ten minutes to a quarter of an hour, if the solution is in
good working order and the thermometer at 60°; but much depends upon the
temperature, and the activity of the Bath. English papers, and especially
the same prepared with Albumen, tone more slowly than foreign papers plain
salted.

The brown and purple tints are an earlier stage of coloration than the
black tones, and therefore the latter require more time. It must be borne
in mind however that prolonged immersion in the Bath is favourable to
sulphuration and yellowness; tending also to render the image unstable
and liable to fade in the half-tones. This fading may not be seen
decidedly whilst the print is in the Bath, but will show itself in the
after-processes of washing and drying.

The ultimate colour of the Print will vary much with the density of the
Negative and the character of the subject; copies of line engravings,
having but little half-tone, are easily obtained of a dark shade
resembling the original impression.

Some advise that on removal from the toning Bath the Print should be
soaked in new Hyposulphite for ten minutes, to complete the fixation;
but this precaution is not required with a Bath of the strength given in
the formula. An analysis of an old Bath which had been extensively used,
indicated only ten grains of Hyposulphite of Silver to the ounce, so that
it was far from saturated.

The occasional addition of fresh crystals of Hyposulphite of Soda to keep
up the strength of the Bath, is useful, the exact quantity added not being
material.

_The washing, drying, and mounting of the Positive Proofs._--It is
essential to wash out every trace of Hyposulphite of Soda from the Print
if it is to be preserved from fading, and to do this properly requires
considerable care.

Always wash with running water when it can be obtained, and choose a large
shallow vessel exposing a considerable surface in preference to one of
lesser diameter. A constant dribbling of water must be maintained for four
or five hours, and the prints should not lie together too closely, or the
water does not find its way between them, (see the remarks at p. 162).

When running water cannot be obtained, proceed as follows:--first wash the
Prints gently, to remove the greater part of the Hyposulphite solution.
Then transfer them to a large shallow pan, in which may be placed as many
Prints as it will conveniently hold. Leave them in for about a quarter
of an hour, with occasional movement, and then pour off the water quite
dry. This point is important, viz. to drain off the last portion of liquid
completely before adding fresh water. Repeat the process of changing at
least five or six times, or more, according to the bulk of water, number
of Prints, and degree of attention paid to them.

Lastly, proceed to remove the size from the Print by immersion in boiling
water.[48] This process will give some idea of the permanency of the
tints, since, if they become dull and red, _and do not darken on drying_,
the Print is probably toned without Gold. Ammonio-Nitrate and plain paper
Prints prepared on foreign papers by the modes described in this Work,
may be expected to stand the test of boiling water; Albumen Prints and
Positives on English paper are a little reddened, although not to an
objectionable degree.

[48] The Print must be well washed in cold water, to remove the
Hyposulphite, before using the hot water; or the half-tones will be liable
to be darkened, or changed to incipient yellowness, by sulphuration. This
point is important as regards the permanency.

The size may also be effectually removed from the Print by the common
Carbonate of Soda used in washing, although the former process is
recommended as the most secure. Dissolve about a handful of the Soda in a
pint of water, and when the milky deposit, if any occurs, has subsided,
immerse the washed Positives for twenty minutes or half an hour. The Soda
renders the paper quite porous, but produces no alteration of tint. If
the process be properly performed, ink will _run_ in attempting to write
upon the back of the finished picture. After removal from the Soda Bath
a second washing will be required, but the time of the first washing may
be proportionally shortened. Here a difficulty will occur with many kinds
of water; the Carbonate of Soda precipitating _Carbonate of Lime_, in the
form of a white powder which obscures the picture. To obviate this, use
_rain water_ until the greater part of the alkaline salt has been removed,
and do not allow a stationary layer of liquid to rest too long upon
the Print. The New River water supplied to many parts of London, being
comparatively soft, answers perfectly, and produces no white deposit, if
the proofs are moved about occasionally.

When the Prints have been thoroughly washed, blot them off between sheets
of porous paper and hang up to dry. Some press them with a hot iron,
which darkens the colour slightly, but does so in an injurious manner when
Hyposulphite of Soda is left in the paper.

Albumen proofs when dry are sufficiently bright without further treatment;
but in the case of plain paper, salted simply, the effect is improved by
laying the Print face downwards upon a square of plate-glass and rubbing
the back with an agate burnisher, sold at the artists' colour-men's. This
hardens the grain of the paper and brings out the details of the picture.
Hot-pressing has a similar effect and is often employed.

Mount the proofs with a solution of Gelatine in hot water, freshly made;
the best Scotch glue answers well. Gum water, prepared from the finest
commercial gum, and free from acidity, may also be used, but it should
be made very thick, that it may not sink into the paper, nor produce an
unpleasant "cockling up" of the cardboard, which is caused by the damp and
expanded print contracting as it dries.

Caoutchouc dissolved in mineral Naphtha to the consistence of thick glue
or gold-beaters' size, is employed by many for mounting Photographic
Prints; it may be obtained at the varnish shops, and is sold in tin
boxes. The mode of using it is as follows:--with a broad brush made of
stiff bristles, apply the cement to the back of the picture; then take a
strip of glass with a straight edge, and by drawing it across the paper,
scrape off as much as possible of the excess. The print will then be
found to adhere very readily to the cardboard, without causing expansion
or cockling; and any portion of the cement which oozes out during the
pressing may, when dry, be removed with a penknife without leaving a stain.

REMARKS UPON THE WANT OF CORRESPONDENCE BETWEEN THE FORMULA OF DIFFERENT
OPERATORS.

The formulæ for Positive printing given in the works on practical
Photography exhibit great variety; and it has been proposed to attempt to
reduce them to more uniform proportions. This cannot however easily be
done, both on account of the difference in the structure and preparation
of the various Photographic papers, and also because the mode of applying
the solutions is not always the same.

Take as an illustration the following process, which has long been
recommended for its simplicity, and which is in every respect a good
one:--Dissolve 40 grains of Chloride of Ammonium in 20 ounces of Distilled
Water, and _immerse_ about a dozen sheets of Towgood's Positive paper,
removing air-bubbles with a camels'-hair brush. When the last sheet has
been placed in the liquid, turn the batch over and take them out one by
one, so that each sheet, remaining in the liquid at least ten minutes,
may be thoroughly saturated. When dry, excite by brushing with a 40 or
60-grain solution of Ammonio-Nitrate of Silver in the usual way.

Now this formula contains less than one-fifth of the amount of salt
often employed, and if a thick foreign paper sized with starch, such as
Canson's Positive, were _floated_ upon such a salting Bath, it would be
difficult to obtain a good picture. By _immersing_ however a paper sized
with Gelatine like the one recommended, a much larger quantity of salt is
retained upon the surface, and the film is sufficiently sensitive. There
are three modes of applying solutions, viz. by brushing, floating, and
immersion. The quantity of solution left on the paper varies with each,
and consequently each requires a different formula. Immersion in a strong
salting Bath tends to give a coarse picture wanting in definition; whereas
the plan of brushing a weak salting solution, produces a paper deficient
in sensitiveness, and yielding a pale red image without proper depth of
shadow.

But independent of these differences, the chemical nature of the _size_
employed also influences the toning of the Print. For instance, in the
process above given, if the Positives, after having been fully toned in
the Gold Bath, and washed in cold water, be treated with _boiling water_,
the tint immediately changes to a dull red; but on blotting off between
sheets of bibulous paper and pressing with a hot iron, the dark tones are
restored.

This destruction of the tint by boiling water, and its restoration by _dry
heat_, is due in great part to the animal substance employed in sizing
the paper; and it will be found that prints upon a foreign paper, such as
the Saxony Positive, salted with a ten-grain solution and sensitized with
Ammonio-Nitrate, do not lose their tones in hot water and are not much
darkened by ironing.

The peculiarity of the sizing of the English Photographic papers must
therefore be borne in mind, and allowance made for the additional
sensitiveness and alteration of colour which it produces. When a formula
is given, the paper which is recommended for that particular formula
should alone be used.

SECTION II.

_Positive Printing by Development._

Negative printing processes will be found useful during the dull winter
months, and at other times when the light is feeble, or when it is
required to produce a large number of impressions from a Negative in a
short space of time. The plan of development also enables the operator to
obtain Positives of greater stability than those yielded by the direct
action of light.

Three processes may be described, the first of which gives Positives of
an agreeable colour, but the second, on Iodide of Silver, the greatest
permanency under unfavourable conditions.

NEGATIVE PRINTING PROCESSES UPON CHLORIDE OF SILVER.

Positives may be obtained by exposing paper prepared with Chloride
of Silver to the action of light until a faint image is perceptible,
and subsequently developing by Gallic Acid; but in this process it
is difficult to obtain sufficient _contrast_ of light and shade; the
impression, if sufficiently exposed and not too much developed, being
feeble, with a want of intensity in the dark parts. By associating
with the Chloride an organic salt of Silver, such as the Citrate, this
difficulty may be overcome, and the shadows be brought out with great
depth and distinctness.

The papers are salted with a mixed Chloride and Citrate as in the formula
for the Ammonio-Nitrate Process.[49] They are then rendered sensitive upon
a Bath of Nitrate of Silver _containing_ either Citric or _Acetic Acid_,
which are used in Negative processes to preserve the clearness of the
white parts under the influence of the developer.

[49] The formula at p. 246 may be modified with advantage: use double the
quantity of Gelatine, and half the amount of Citrate and Chloride.

The Bath of Aceto-Nitrate is prepared as follows:--

  Nitrate of Silver                       30 grains.
  Glacial Acetic Acid                     30 minims.
  Water                                    1 fluid ounce.

Float the papers (Papier Saxe or Papier Rive) upon the Bath for three
minutes, and suspend them to dry in a room from which actinic rays are
_perfectly_ excluded.

The exposure to light,--which is conducted in the ordinary printing frame,
the Negative and sensitive paper being laid in contact in the usual
way,--will seldom be longer than three or four minutes, even upon a dull
day. It may be regulated by the colour assumed by the projecting margin
of the paper; but it is quite possible to tell by the appearance of the
image when it has received a sufficient amount of exposure:--the whole of
the picture should be seen, excepting the _lightest shades_, and it will
be found that very few details can be brought out in the development which
were altogether invisible before the Gallic Acid was applied.

The developing solution is prepared as follows:--

  Gallic Acid                              2 grains.
  Water                                    1 fluid ounce.

In very cold weather it may be necessary to employ a saturated solution of
Gallic Acid, containing about four grains to the ounce; whereas in warm
weather the image will develope too quickly, and Acetic Acid must be added
(see the remarks at the end of the process, p. 266).

To facilitate the solution of the Gallic Acid, stand the bottle in a warm
place near the fire. A lump of Camphor floated in the liquid, or a drop
of Oil of Cloves added, will to a great extent prevent it from becoming
mouldy by keeping; but if once mould has formed, the bottle must be well
cleansed with Nitric Acid, or the decomposition of the fresh Gallic Acid
will be hastened.

Pour the solution of Gallic Acid into a flat dish, and immerse the Prints
two or three at a time, moving them about, and using a glass rod to remove
air-bubbles. The development is rapid, and will be completed in three or
four minutes. If the Print developes slowly, becomes _very dark in colour_
by continuing the action of the Gallic Acid, but shows no half-tones,
it has not been exposed sufficiently long to the light. An over-exposed
proof, on the other hand, developes with unusual rapidity, and it is
necessary to remove it speedily from the Bath in order to preserve the
clearness of the white parts; when taken out to the light, it appears pale
and red, with no depth of shadow.

The extent to which the development should be carried depends upon the
kind of Print desired. By pushing the action of the Gallic Acid, a dark
picture not much altered by the fixing Bath will be produced. But a better
result as regards colour and gradation of tone will be obtained by
removing the Print from the developing solution whilst in the light red
stage, and toning it subsequently by means of Gold; in which case it will
correspond both in appearance and properties to a Positive obtained by the
direct action of light (see the remarks at page 167).

When it is intended to follow the latter plan, the action of the developer
must be stopped at a point when the proof appears lighter than it is to
remain; since the Sel d'or Bath adds a little to the intensity, and the
image becomes somewhat more vigorous on drying.

Wash the Prints in cold water in order to extract all the Gallic Acid.
Then tone with _Sel d'or_ in the manner described in the next Section, and
fix in the usual way. The whites will with care be kept pure; or with only
a faint yellow tinge, which is not objectionable.

Upon comparing the developed Prints with others obtained by the direct
action of light upon the same sensitive paper, it is evident that the
advantage is _slightly_ on the side of the latter; but the difference is
so small that it would be overlooked in printing large subjects, for which
the Negative Process is more especially adapted. The _colour_ of both
kinds of Positives is the same, or perhaps a shade darker in the developed
proofs, which are usually of a violet-purple tone, but sometimes of a dark
chocolate-brown.

_A developing process with Serum of Milk._--The use of "whey" as a vehicle
for Chloride of Silver has something the same effect as that produced by
adding a Citrate. This may be traced to the presence of the Milk Sugar and
of a portion of uncoagulated Caseine left in the Serum.

The only difficulty in the process is to coagulate the milk in such a
way as to separate the greater part but not the whole of the Caseine.
Milk which has become sour, or to which an acid has been added, is not
considered so good for the purpose as that which has been treated with
rennet; and even when rennet is used it must be of the best quality or
its action will be imperfect. The serum must filter clear through,
blotting-paper; but it should not run very rapidly, or in all probability
the whole of the Caseine has been separated, and the fluid contains little
besides sugar. The whey which is left after cheese-making, commonly
answers the purpose, if clarified by beating it up with the white of
an egg and subsequently boiling and filtering. Globules of oil must be
separated as far as possible, or they will produce a greasiness of the
paper.[50]

[50] See the Vocabulary, Part III,, Art. "Milk," for further particulars.

Salt the prepared Serum with Chloride of Sodium or Ammonium; in quantity
about eight or ten grains to each fluid ounce, and render sensitive upon
the same Bath as that recommended for the Citrate Process.

A NEGATIVE PRINTING PROCESS UPON IODIDE OF SILVER.

Iodide of Silver is more sensitive to the reception of the invisible image
than the other compounds of that metal; and hence it is usefully employed
in printing _enlarged_ Positives from small Negatives, by means of the
Camera. The great stability of the proofs upon Iodide of Silver will also
be a recommendation of this process when unusual permanency is required.

Take of

  Iodide of Potassium                    160 grains.
  Water                                   20 fluid ounces.

The best paper to use will be either Turner's Calotype, or Whatman's or
Hollingworth's Negative; the foreign papers do not succeed with the above
formula (p. 258).

Float the paper on the iodizing Bath until it ceases to curl up and lies
flat upon the liquid: then pin up to dry in the usual way.

Render sensitive upon a Bath of Aceto-Nitrate of Silver containing 30
grains of Nitrate of Silver with 30 minims of Glacial Acetic Acid to each
ounce of water.

When the sheet is quite dry, place it in contact with the Negative in a
pressure frame, and expose _to a feeble light_. About 30 seconds will be
an average time upon a dull winter's day, on which it would be impossible
to print at all in the ordinary way. On removing the Negative nothing
whatever is seen upon the paper, the image being strictly invisible in
this process unless the exposure has been carried too far.

Develope by immersion in a saturated solution of Gallic Acid, prepared
in the manner described at page 261. The image appears slowly, and the
process may last from 15 minutes to half an hour. If the exposure has
been correctly timed, the Gallic Acid appears at length almost to cease
acting; but when the proof has been over-exposed, the development goes
on uninterruptedly, and the image becomes too dark, partaking more
of the character of a Negative than a Positive. The usual rule, that
_under_-exposed proofs develope slowly but show no half-tones, and that
the _over_-exposed develope with unusual rapidity, is also observed in the
process with Iodide of Silver.

After the picture is fully brought out, wash in cold, and subsequently
in warm water, to remove the Gallic Acid, which, if allowed to remain,
would discolour the Hyposulphite Bath. Then fix the Print in a solution
of Hyposulphite of Soda, one part to two of water, continuing the action
until the yellow colour of the Iodide disappears. The fixing Bath ought
not to produce much change in the tint. If the Positive loses its dark
colour on immersion in the Hyposulphite, and becomes pale and red,
it has been insufficiently developed. The theory of this part of the
process should be understood:--It is particularly the _second stage_ of
the development of a Photograph (see p. 144) on which the fixing Bath
produces no effect; and therefore a considerable change of colour in the
Hyposulphite indicates that too little Silver has been deposited, and the
remedy will be to push the development, adding a little Aceto-Nitrate to
the Gallic Acid if the strength of the Bath be found insufficient to yield
dark tones.

The colour of Positives developed upon Iodide of Silver is not agreeable,
and they become blue and inky when toned with gold. By fixing the proof
in Hyposulphite of Soda which has been long used and has acquired
sulphuretting properties, the tint is much improved; but the permanency of
the Print under unfavourable conditions is lessened by adopting that mode
of toning.

A NEGATIVE PRINTING PROCESS UPON BROMIDE OF SILVER.

By substituting the Bromide for the Iodide of Silver in the above process,
the proportions and details of manipulation being in other respects the
same, a more agreeable colour is obtained.

Paper prepared with Bromide of Silver is less sensitive than the Iodide,
but an exposure of one minute (in the printing frame) will usually be
sufficient even on a dull day. The image is nearly latent, but sometimes a
very faint outline of the darkest shadows can be seen. The proportion of
Bromide used is likely to influence this point; the sensitiveness being
diminished, but the image showing more of the details before development,
when the quantity of the Silver Salt is reduced to a minimum.

Either English or French papers may be used, but in the latter case the
Bromide should be dissolved in Serum of Milk (p. 262), or it will be
difficult to obtain a good surface picture. The proportion of Bromide may
be five grains to the ounce of Serum.

These proofs, even when simply fixed in plain Hyposulphite of Soda, are
superior in colour to the Positives printed by the last formula upon
Iodide of Silver; and the permanency is very great if the development be
sufficiently pushed. The use of the Serum of Milk gives an advantage in
resisting the oxidizing influences to which Positives are liable to be
exposed (p. 150).

GENERAL REMARKS ON NEGATIVE PRINTING.

Printing by development should not be attempted until the manipulation of
the ordinary process by direct exposure to light has been acquired.

Perfect cleanliness is essential. The salting or iodizing solution and
the Aceto-Nitrate Bath must be filtered clear, as the effect of small
suspended particles in producing spots is more seen when the image is
brought out by a developer.

It will be necessary to be far more careful in excluding white light
than in the ordinary process; and when Iodide of Silver is used, all the
precautions required in the case of Collodion Negatives must be taken.

Observe particularly that the dishes are kept clean, or the Gallo-Nitrate
of Silver will be rapidly discoloured (read the remarks at page 179).

Stereoscopic Negatives and small portraits are not successfully printed
by development; since it is difficult to obtain the most elaborate
definition, and there is a slight tendency to yellowness in the white
parts. Positives may be developed upon Albumen paper, but the Gallic Acid
is apt to discolour the lights.

In printing by development upon Chloride of Silver, the theory of the
subject must be particularly studied. When the weather is cold and the
light bad, the development of the image proceeds slowly, the Gallic Acid
Bath remains clear, and good half-tones are obtained; but under opposite
conditions, the developer may become turbid and the shadows be lost by
excessive deposit of Silver. This _over-development_ will be remedied by
printing the Negative in a more feeble light (near to the open window of
a room), and by adding Acetic Acid to the developer, about 5 or 10 minims
to the ounce, so as to bring out the image more slowly. The intensity of
action is thus lessened, and if the picture be not under-exposed, the
half-tones will be good.

Observe also when preparing papers with Citrate, that if too much
Carbonate of Soda be added in neutralizing the Citric Acid, Carbonate
of Silver will be deposited in the paper, the effect of which is to
remove by degrees the acidity of the Nitrate Bath, and to produce
over-development and excessive sensibility to light.

The colour of the proofs when taken from the Gallic Acid should be
_light red_; the gradation of tone not being usually so perfect when the
development is carried into the second or black stage.

It is not recommended to prepare too large a stock of the salted papers,
as they will probably be liable to mouldiness and decomposition unless
kept perfectly dry.

SECTION III.

_The Sel d'or Process for toning Positives._

This process is somewhat more troublesome than the plan of fixing and
toning in one solution, but possesses advantages which will presently be
enumerated. The description may be divided into the preparation of the
toning Bath, and the manipulatory details.

THE PREPARATION OF THE TONING BATH.

Take of

  Chloride of Gold                         1 grain.
  Pure Hyposulphite of Soda                3 grains.
  Hydrochloric Acid                        4 minims.
  Water, distilled or common               4 fluid ounces.

Dissolve the Gold and Hyposulphite of Soda each in two ounces of the
water; then mix quickly by pouring the former solution into the latter,
and add the Hydrochloric Acid. If the Chloride of Gold be neutral, the
liquid will have a red tinge, but if _acid_, then the solution may be
colourless. The commercial Chloride of Gold, containing usually much free
Hydrochloric Acid, will not require any addition of that substance. (See
the Vocabulary, Part III.)

In place of making an extemporaneous Hyposulphite of Gold by mixing the
Chloride with Hyposulphite of Soda, the Crystallized Sel d'or may be used,
adding about half a grain to the ounce of water, acidified as before; but
the objection to the employment of this salt is its expense, and also the
difficulty of obtaining it in a pure form; some samples containing less
than five per cent, of Gold.

It will be found very convenient to keep the two solutions on hand ready
for mixing, viz. the Chloride of Gold dissolved in water in the proportion
of a grain to the drachm, and the Hyposulphite of Soda, three grains to
the drachm. When required for use, measure out a fluid drachm of each,
dilute with water to two ounces, and mix.

It is possible that the three-grain solution of Hyposulphite of Soda may
by long keeping become decomposed, with precipitation of Sulphur. The
effect of this would be to produce a turbidity and deposit of Gold on
mixing the ingredients for the Bath, the Chloride of Gold being in excess
over the Hyposulphite of Soda (see p. 250).

The Bath of Sel d'or is always most active when recently mixed, but it
will keep good for some days if contact with free Nitrate of Silver be
avoided. The addition of this substance produces a red deposit in the
Bath, containing Gold, and the solution then becomes useless.

DETAILS OF MANIPULATION.

The paper may be prepared by either of the formulæ given in the first
Section of this Chapter, according to the tint desired. The pure black
tones are obtained most easily with the Ammonio-Nitrate paper, and the
purple tints, without gloss, on paper prepared with plain Chloride and
Citrate of Soda.

The printing is not carried quite to the usual intensity, as the
half-tones are very little dissolved in this process.

On being taken from the frame, the prints are washed thoroughly in common
water until it ceases to become milky; that is, until the greater part of
the Nitrate of Silver has been removed. The washing must be conducted in a
dark place, but it is not necessary to hasten it; the proofs may be thrown
into a pan of water covered with a cloth, and allowed to remain until
required for tinting.

A trace of free Nitrate of Silver usually escapes the washing; this would
cause a yellow deposit on the Print, and also in the toning Bath. It must
therefore be removed, either by adding a little _common salt_ to the water
during the last washings, or by means of a dilute solution of Ammonia.

For plain paper Prints the former plan will be found the least
troublesome; but with Albumen proofs[51] the Ammonia is required, in order
to dissolve away a portion of the Albuminate of Silver which has escaped
the action of light, before submitting the print to the gold; otherwise
the dark tones would nearly disappear in the fixing Bath, the Hyposulphite
carrying away the Gold with this superficial layer of silver salt.

[51] The amateur is recommended not to use Albuminized paper in this
process until he has become accustomed to the manipulations; the plain
paper prints being toned with more ease and certainty.

To prepare the Ammonia Bath, take of

  Liquor Ammoniæ                           1 drachm.
  Common Water                             1 pint.

The exact quantity is not material; if the liquid smells faintly of
Ammonia, it will be sufficient. Place the washed Prints in this Bath, two
or three at a time, and allow them to remain until the purple tint gives
place to a red tone. The action must be watched, because if the Ammonia
Bath be strong, the proof becomes unusually _pale and red_, and when this
is the case a little brilliancy is lost in the after-tinting.

As the Print is comparatively insensitive to light when the excess of
Nitrate has been washed away, it is not necessary to darken the room; but
a _bright light_ proceeding from an open door or window should be avoided.

After using the salt or the Ammonia, soak the Prints again for a minute
or so in common water. Then place them in the toning Bath of Gold and
acid; do not put in too many at once, and move them about occasionally, to
prevent spots of imperfect action at the point where the sheets touch each
other.

The foreign papers, plain salted, colour rapidly in two or three minutes.
English papers require five to ten minutes; Albuminized, ten minutes to
a quarter of an hour. The tendency of the Gold Bath is to give a blue
tone to the image; hence proofs which are light red after using the salt
or Ammonia, become, first red-purple, and then violet-purple in the Sel
d'or. Albumen Prints assume some shade of brown, or of purple if not too
strongly Albuminized. Ammonio-Nitrate papers highly salted, and prepared
without Citrate, become first dark purple, and then blue and inky; the
Citrate is intended to obviate this inky tint.

When the darkest tones are reached, the Bath produces no further effect,
but eventually (more especially if the solution be not shielded from light
[?]) there is a little decomposition, producing a cream-coloured deposit
upon the lights.

The toning being completed, the Prints are again washed for an instant in
water, to remove the excess of gold solution. This washing must not be
continued longer than two or three minutes, or there will be danger of
yellowness of the whites; this however ought not to happen with proper
precautions.

Lastly, the proofs are fixed in a solution of Hyposulphite of Soda, one
part to four of water; which may be used many times successively. This
Bath alters the tone very little if the deposit of Gold be well fixed
on the Print; but the writer has often observed in the case of Albumen
paper and paper prepared with Citrate (Formula II.) that if removed too
quickly from the Sel d'or, the purple tones change by immersion in the
Hyposulphite to a chocolate-brown. Ammonio-Nitrate Prints are less liable
to alter in this way.

In order that the fixing may be properly performed, the time of immersion
should not be less than ten minutes with a porous paper, plain salted; or
fifteen minutes in the case of an English or albuminized paper.

Ammonia may be used for fixing plain paper Prints; about one part of the
Liquor Ammoniæ, to four of water. Ten minutes' immersion will usually be
sufficient, and the tone is very little affected. This process is a good
one, but the pungent smell of the Ammonia is an objection, and the Bath
discolours by use. Some care too is required in order to ensure a proper
fixing of the prints (see the remarks at page 131).

For directions to wash and mount the proofs, see page 255.

It will sometimes happen in the Sel d'or process, from the toning Bath
having but little solvent action on the light shades, that the Prints,
after being washed and dried, appear too dark; this may be remedied by
laying them for a few minutes in _a very dilute solution_ of Chloride
of Gold (five or six drops of the yellow solution of the Chloride to a
few ounces of water) and washing for an additional quarter of an hour.
Or an over-printed Positive may be saved by toning it with Chloride of
Gold instead of Sel d'or. In that case, after proper removal of the free
Nitrate of Silver, a few drops of a lemon-yellow solution of Chloride of
Gold (with a fragment of Carbonate of Soda added to remove acidity, p.
132), should be poured over the Print, which is to be subsequently fixed
in the usual way.

_Advantages of toning by Sel d'or._--This process will be found especially
useful by those who print large Positives. The solutions may be mixed in
a few minutes, and, being very dilute, are economical. It is not even
necessary to employ a _Bath_ for toning, but if the Sel d'or solution be
prepared of about twice or three times the strength given in the formula,
it will be sufficient to pour a few drachms upon the surface of the
print. As the Gold solution is always used soon after mixing, a uniform
and permanent tint can be obtained; whereas the single fixing and toning
Bath of Gold and Hyposulphite loses much of its efficacy by keeping, and
_over-printing_ of the proof is required in proportion as the Bath becomes
older.

SECTION IV.

_On a mode of Printing enlarged and reduced Positives, Transparencies,
etc., from Collodion Negatives._

To explain the manner in which a Photograph may be enlarged or reduced in
the process of printing, it will be necessary to refer to the remarks made
at page 52, on the _conjugate foci_ of lenses.

If a Collodion Negative be placed at a certain distance in front of a
Camera, and (by using a tube of black cloth) the light be admitted into
the dark chamber only through the Negative, a reduced image will be formed
upon the ground glass; but if the Negative be advanced nearer, the image
will increase in size, until it becomes first equal to, and then larger
than, the original Negative; the focus becoming more and more distant from
the lens, or receding, as the Negative is brought nearer.

Again, if a Negative portrait be placed in the Camera slide, and
the instrument being carried into a dark room, a hole be cut in the
window-shutter so as to admit light through the Negative, the luminous
rays, after refraction by the lens, will form an image of the exact size
of life upon a white screen placed in the position originally occupied
by the sitter. These two planes, in fact, that of the object and of the
image, are strictly _conjugate foci_, and, as regards the result, it is
immaterial from which of the two, anterior or posterior, the rays of light
proceed.

Therefore in order to obtain a reduced or enlarged copy of a Negative, it
is necessary only to form an image of the size required, and to project
the image upon a sensitive surface either of Collodion or paper.

A good arrangement for this purpose may be made by taking an ordinary
Portrait Camera, and prolonging it in front by a deal box blackened inside
and with a double body, to' admit of being lengthened out as required; or,
more simply, by adding a framework of wood covered in with black cloth. A
groove in front carries the Negative, or receives the slide containing the
sensitive layer, as the case may be.

In _reducing_ Photographs, the Negative is placed in front of the lens, in
the position ordinarily occupied by the object; but in making an enlarged
copy, it must be fixed _behind_ the lens, or, which is equivalent, the
lens must be turned round, so that the rays of light transmitted by the
Negative enter the back glass of the combination, and pass out at the
front. This point should be attended to in order to avoid indistinctness
of image from spherical aberration.

A Portrait combination of lenses of 2-1/2 or 3-1/4 inches diameter
is the best form to use, and the actinic and luminous foci should
accurately correspond, as any difference between them would be increased
by enlarging. A stop of an inch or an inch and a half aperture placed
_between_ the lenses obviates to some extent the loss of sharp outline
usually following enlargement of the image.

The light may be admitted through the Negative by pointing the Camera
towards the sky; or direct sunlight may be used, thrown upon the Negative
by a plane reflector. A common swing looking-glass, if clear and free from
specks, does very well; it should be so placed that the centre on which it
turns is on a level with the axis of the lens.

The best Negatives for printing enlarged Positives are those which are
distinct and clear; and it is important to use a _small_ Negative, which
strains the lens less and gives a better result than one of larger size.
In printing by a 2-1/4 lens for instance, prepare the Negative upon a
plate about two inches square, and afterwards enlarge it four diameters.

Paper containing Chloride of Silver is not sufficiently sensitive to
receive the image, and the Print should be formed upon Collodion, or on
iodized paper developed by Gallic Acid (see p. 263).

The exposure required will vary not only with the intensity of the light
and the sensibility of the surface used, but also _with the degree of
reduction or enlargement of the image_.

In printing upon Collodion the resulting picture is Positive by
transmitted light; it should be backed up with white varnish, and then
becomes Positive by reflected light. The tone of the blacks is improved
by treating the plate first with Bichloride of Mercury, and then with
Ammonia, in the manner described at pages 113 and 207.

Mr. Wenham, who has written a paper on the mode of obtaining Positives
of the life size, operates in the following way:--he places the Camera,
with the slide containing the Negative, in a dark room, and reflects the
sunlight in through a hole in the shutter, so as to pass first through the
Negative and then through the lens; the image is received upon iodized
paper, and developed by Gallic Acid, in the mode described in the second
Section of this Chapter (p. 263).

_On printing Collodion transparencies for the Stereoscope._--This may
be done by using the Camera to form an image of the Negative in the
mode described in the last page; but more simply by the following
process:--Coat the glass, upon which the Print is to be formed, with
Collodio-Iodide of Silver in the usual way; then lay it upon a piece of
black cloth, Collodion side uppermost, and place two strips of paper of
about the thickness of cardboard and one-fourth of an inch broad, along
the two opposite edges, to prevent the Negative being soiled by contact
with the film. Both glasses must be _perfectly flat_, and even then it may
happen that the Negative is unavoidably wetted; if so, wash it immediately
with water, and if it be properly varnished, no harm will result.