Two or Three Shallow Dishes, for holding distilled water, iodide,
potassium, &c.--the same water never being used for two different
operations.
White Bibulous Paper.
Photogenic Camera--Fig. 9.
Pressure Frame--Fig 29.
Paper, of the very best quality--directions for the choice of which
have been already given.
A Screen of Yellow Glass.
Camels' or Badgers' hair Brushes:--A seperate one being kept for each
wash and solution, and which should be thoroughly cleansed immediately
after using in distilled water. That used for the gallo-nitrate is
soon destroyed, owing to the rapid decomposition of that preparation.
A Graduated Measure.
Three or Four Flat Boards, to which the paper may be fixed with drawing
pins.
A Hot Water Drying Apparatus, for drying the paper will also be found
useful.
In preparing the Calotype paper, it is necessary to be extremely
careful, not only to prevent the daylight from impringing upon it, but
also to exclude, if possible, the strong glare of the candle or lamp.
This may be effected by using a shade of yellow glass or gauze, which
must be placed around the light. Light passing through such a medium
will scarcely affect the sensitive compounds, the yellow glass
intercepting the chemical rays.
Preparation of the Iodized Paper.--Dissolve one hundred grains of
crystalized nitrate of silver in six ounces of distilled water, and
having fixed the paper to one of the boards, brush it over with a soft
brush on one side only with this solution, a mark being placed on that
side whereby it may be known. When nearly dry dip it into a solution
of iodide of potassium, containing five hundred grains of that salt
dissolved in a pint of water. When perfectly saturated with this
solution, it should be washed in distilled water, drained and allowed
to dry. This is the first part of the process, and the paper so
prepared is called iodized paper. It should be kept in a port-folio or
drawer until required: with this care it may be preserved for any
length of time without spoiling or undergoing any change.
Mr. Cundell finds a stronger solution of nitrate of silver preferable,
and employs thirty grains to the ounce of distilled water: he also adds
fifty grains of common salt to the iodide of potassium, which he
applies to the marked side of the paper only. This is the first
process.
Preparation of the paper for the Camera.--The second process consists
in applying to the above a solution which has been named by Mr. Talbot
the "Gallo-Nitrate of Silver;" it is prepared in the following manner:
Dissolve one hundred grains of crystalized nitrate of silver in two
ounces of distilled water, to which is added two and two-third drachms
of strong acetic acid. This solution should be kept in a bottle
carefully excluded from the light. Now, make a solution of gallic acid
in cold distilled water: the quantity dissolved is very small. When
it is required to take a picture, the two liquids above described
should be mixed together in equal quantities; but as it speedily
undergoes decomposition, and will not keep good for many minutes, only
just sufficient for the time should be prepared, and that used without
delay. It is also well not to make much of the gallic acid solution,
as it will not keep for more than a few days without spoiling. A sheet
of the iodized paper should be washed over with a brush with this mixed
solution, care being taken that it be applied to the marked side. This
operation must be performed by candle light. Let the paper rest half a
minute, then dip it into one of the dishes of water, passing it beneath
the surface several times; it is now allowed to drain, and dried by
placing its marked side upwards, on the drying apparatus. It is better
not to touch the surface with bibulous paper. It is now highly
sensitive, and ready to receive the impression. In practice it is
found better and more economical not to mix the nitrate of silver and
gallic acid, but only to brush the paper with the solution of the
nitrate.
Mr. Talbot has recently proposed some modifications in his method of
preparing the calotype paper. The paper is first iodized in the usual
way; it is then washed over with a saturated solution of gallic acid in
distilled water and dried. Thus prepared he calls it the io-gallic
paper: it will remain good for a considerable time if kept in a press
or portfolio. When required for use, it is washed with a solution of
nitrate of silver (fifty grains to the ounce of distilled water), and
it is then fit for the camera.
Exposure in the Camera.--The calotype paper thus prepared possesses a
very high degree of sensibility when exposed to light, and we are thus
provided with a medium by which, with the aid of the photogenic camera,
we may effectually copy views from nature, figures, buildings, and even
take portraits from the shadows thrown on the paper by the living face.
The paper may be used somewhat damp. The best plan for fixing it in
the camera is to place it between a piece of plate glass and some other
material with a flat surface, as a piece of smooth slate or an iron
plate, which latter, if made warm, renders the paper more sensitive,
and consequently the picture is obtained more rapidly.
Time of Exposure.--With regard to the time which should be allowed for
the paper to remain in the camera, no direct rules can be laid down;
this will depend altogether upon the nature of the object to be copied,
and the light which prevails. All that can be said is, that the time
necessary for forming a good picture varies from thirty seconds to five
minutes, and it will be naturally the first object of the operator to
gain by experience this important knowledge.
Bringing Out the Picture.--The paper when taken from the camera, which
should be done so as to exclude every ray of light--and here the dark
slide of the camera plate holder becomes of great use--bears no
resemblance to the picture which in reality is formed. The impression
is latent and invisible, and its existence would not be suspected by
any one not acquainted with the process by previous experiment. The
method of bringing out the image is very simple. It consists in
washing the paper with the gallo-nitrate of silver, prepared in the way
already described, and then warming it gently, being careful at the
same time not to let any portion become perfectly dry. In a few
seconds the part of the paper upon which the light has acted will begin
to darken, and finally grow entirely black, while the other parts
retain their original color. Even a weak impression may be brought out
by again washing the paper in the gallo-nitrate, and once more gently
warming it. When the paper is quite black, as is generally the case,
it is a highly curious and beautiful phenomenon to witness the
commencement of the picture, first tracing out the stronger outlines,
and then gradually filling up all the numerous and complicated details.
The artist should watch the picture as it developes itself, and when in
his judgment it has attained the greatest degree of strength and
clearness, he shall stop further proceedings by washing it with the
fixing liquid. Here again the mixed solution need not be used, but the
picture simply brushed over with the gallic acid.
The Fixing Process.--In order to fix the picture thus obtained, first
dip it into water; then partly dry it with bibulous paper, and wash it
with a solution of bromide of potassium--containing one hundred grains
of that salt dissolved in eight or ten ounces of distilled water. The
picture is again washed with distilled water, and then finally dried.
Instead of bromide of potassium, a solution of hyposulphite of soda, as
before directed, may be used with equal advantage.
The original calotype picture, like the photographic one described in
the last chapter, is negative, that is to say, it has its lights and
shades reversed, giving the whole an appearance not conformable to
nature. But it is easy from this picture to obtain another which shall
be conformable to nature; viz., in which the lights shall be
represented by lights, and the shades by shades. It is only necessary
to take a sheet of photographic paper (the bromide paper is the best),
and place it in contact with a calotype picture previously rendered
transparent by wax or oil as before directed. Fix it in the frame,
Fig. 29, expose it in the sunshine for a short time, and an image or
copy will be formed on the photogenic paper. The calotype paper itself
may be used to take the second, or positive, picture, but this Mr.
Talbot does not recommend, for although it takes a much longer time to
take a copy on the photogenic paper, yet the tints of such copy are
generally more harmonious and agreeable. After a calotype picture has
furnished a number of copies it sometimes grows faint, and the
subsequent copies are inferior. This may be prevented by means of a
process which revives the strength of the calotype pictures. In order
to do this, it is only necessary to wash them by candlelight with
gallo-nitrate of silver, and then warm them. This causes all the
shades of the picture to darken considerably, while the white parts are
unaffected. After this the picture is of course to be fixed a second
time. It will then yield a second series of copies, and, in this way,
a great number may frequently be made.
The calotype pictures when prepared as we have stated, possess a
yellowish tint, which impedes the process of taking copies from them.
In order to remedy this defect, Mr. Talbot has devised the following
method. The calotype picture is plunged into a solution consisting of
hyposulphite of soda dissolved in about ten times its weight of water,
and heated nearly to the boiling point. The picture should remain in
about ten minutes; it must then be removed, washed and dried. By this
process the picture is rendered more transparent, and its lights become
whiter. It is also rendered exceedingly permanent. After this process
the picture may be waxed, and thus its transparency increased. This
process is applicable to all photographic papers prepared with
solutions of silver.
Having thus fully, and it is hoped clearly, considered the process, it
may be necessary before dismissing the calotype from notice, to add one
or two remarks from the observations and labors of some who have
experimented in this art. Dr. Ryan in his lectures before the Royal
Polytechnic Institution, has observed, that in the iodizing process the
sensitiveness of the paper is materially injured by keeping it too long
in the solution of iodide of potassium, owing to the newly formed
iodide of silver being so exceedingly solvable in excess of iodide of
potassium as in a few minutes to be completely removed. The paper
should be dipped in the solution and instantly removed. There is
another point, too, in the preparation of the iodized paper in which
suggestions for a slight deviation from Mr. Talbot's plan have been
made. In the first instance, it is recommended that the paper be
brushed over with the iodide of potassium, instead of the nitrate of
silver, transposing, in fact, the application of the first two
solutions. The paper, having been brushed over with the iodide of
potassium in solution, is washed in distilled water and dried. It is
then brushed over with nitrate of silver, and after drying is dipped
for, a moment in a fresh solution of iodide of potassium of only
one-fourth the strength of the first, that is to say, one hundred and
twenty-five grains of the salt to a pint of water. After this it is
again washed and dried. The advantage derived from this method, is a
more sensitive paper, and a more even distribution of the compounds
over the surface.
Another deviation from Mr. Talbot's method has been suggested, as
follows:
Brush the paper over with a solution of one hundred grains of nitrate
of silver to an ounce of water. When nearly, but not quite, dry, dip
it into a solution of twenty-five grains of iodide of potassium to one
ounce of distilled water, drain it, wash it in distilled water and
again drain it. Now brush it over with aceto-nitrate of silver, made
by dissolving fifty grains of nitrate of silver in one ounce of
distilled water, to which is added one sixth of its volume of strong
acetic acid. Dry it with bibulous paper, and it is ready for receiving
the image. When the impression has been received, which will require
from one to five minutes according to the state of the weather, it must
be washed with a saturated solution of gallic acid to which a few drops
of the aceto-nitrate of silver, made as above, have been added. The
image will thus be gradually brought out, and may be fixed with
hyposulphite of soda. To obtain the positive picture, paper must be
used brushed over with an ammonio-nitrate of silver, made thus: forty
grains of nitrate of silver is to be dissolved in one ounce of
distilled water, and liquid ammonia cautiously added till it
re-dissolves the precipitate.
A pleasing effect may be given to calotype, or indeed to all
photographic pictures, by waxing them at the back, and mounting them on
white paper, or if colored paper be used, various beautiful tones of
color are produced.