[The following paper, which has been kindly communicated to us by MR.
POLLOCK at the request of DR. DIAMOND, describes a process which
deserves the especial attention of our photographic friends, for the
beauty and uniformity of its results.]
MR. POLLOCK'S DIRECTIONS FOR OBTAINING POSITIVE PHOTOGRAPHS UPON
ALBUMENISED PAPER.
_The paper_ should be carefully chosen, by holding up every sheet to the
light, and only those sheets which are homogeneous in appearance and free
from spots should be kept for use.
_The albumen_ should be obtained from new-laid hens' eggs; twenty-four is a
convenient number to use at a time: these will yield twenty-four ounces of
albumen, to which should be added six ounces of distilled writer (making
thirty ounces in all) and four per cent. of chloride of ammonium, viz. one
ounce and a quarter.
The albumen water and chloride should be whipped with a silver fork for
several minutes, and then put into a narrow tall jar, and allowed to stand
for not less than two days (forty-eight hours). In cool weather it will
keep well for eight days, at the end of which time the upper half of the
albumen is to be poured off into a shallow vessel, rather larger than the
sheets of paper intended to be albumenised.
_To put the Albumen on the Paper._--Take a sheet by two opposite corners;
turn one up; place the sheet boldly on the albumen, the centre first coming
in contact with the albumen; lower the corners of the paper, gradually
carefully excluding, the air. Let the sheet so placed remain four minutes:
then take it by the turned up corner, and rip it from the albumen quickly,
so as to carry up a quantity of the albumen with it. Let it drain for a
minute or two, moving it so as not to allow the albumen to run in streaks;
pin it to a piece of tape; and, when dry, pass a very hot iron over the
back. This ends the albumenising process.
_To make the Paper sensitive._--Place the albumenised side downwards, for
four minutes, on the surface of a solution of nitrate of silver, of the
strength of ninety grains to the ounce of distilled water; pin it up by one
corner to dry, and keep it between pieces of blotting-paper. This must be
done by yellow light, or the light of a candle.
_To print from the Negative._--The simplest apparatus to have is a number
of pieces of plate-glass a quarter of an inch thick, colourless, about
twelve inches by ten in size.
The sensitive paper is to be placed on one of the plates of glass,
sensitive side upwards, and the negative is to be placed firmly upon it,
collodion side downwards; and a second glass plate is then to be placed on
the negative, and the whole arrangement exposed to the light. The time for
exposure is from three minutes to an hour. With a little practice the
negative can be lifted up, and the positive viewed front time to time,
without any risk of displacement.
The best rule is to print the lightest shade on the positive very decidedly
darker than it would be wished that it should remain permanently.
_To fix the Positive._--On removing it from the pressure frame, place it in
a bath made as follows:
Water 6 oz.
Hyposulphite of soda 1 oz.
Nitrate of silver solution, 50 grs. to oz. 15 minims.
Iodide of silver, dissolved in a saturated
solution of hypo. 10 minims.
Chloride of gold 2 grains.
Chloride of silver (blackened by light) 5 grains.
Acetic acid 2 drops.
Mix these: let them stand some hours; and filter before use. If the
chloride of silver is omitted, the bath will do very well, but will very
much improve with age, as it will acquire chloride of silver from the
positives placed in it. {582}
The time to leave the positive in the fixing bath varies from one hour to
twelve. To get good black and white tints, the average time is five or six
hours. When the desired tint is obtained, remove it into a bath composed of
Water 6 oz.
Hypo. 1 oz.
Leave in this for half an hour, and then keep it in running water for
several hours. If the water is hot, the time of soaking may be lessened:
boiling water is objectionable. Nearly dry the positive between sheets of
clean blotting-paper, and finish it by passing a very hot iron over it.
_General Remarks._--The albumenised paper will keep any length of time in a
dry place.
When made sensitive, as directed, it will keep three days, always supposing
that it is both prepared and kept most carefully excluded from white light.
If, instead of a solution of nitrate of silver of ninety grains to the
ounce, a weaker one be used, to make the paper sensitive, it will keep when
sensitive a much longer time,--with a thirty-grain solution, a fortnight,
or sometimes even a month; but then it does not give a positive of the same
force and tone as that obtained with the stronger solution.
After the fixing bath has done its day's work, it should be poured back
into the bottle from which it came, and the bottle be filled up from the
finishing bath; and so the bath is kept always of the same quantity; and by
adding from time to time chloride of gold, it is kept of the same quality.
The nitrate of silver and chloride of silver will never have to be renewed.
The iodide of silver should be added as at first, viz. ten drops for about
every two hundred positives fixed; and the acetic acid, viz. two drops for
about every four hundred.
In a bath of twenty-four ounces, as many as thirty positives, five inches
by four, may be placed at one time: but the dark tints will then appear
very slowly and gradually.
To insure a good positive, next to having a good negative, it is most
important to print of the right depth, neither too much nor too little.
Great attention should be paid to this: for the finest tints are only to be
obtained in positives exposed exactly the right time.
Positives printed in a bright sun quickly are always better than those
obtained by longer exposure without sun.