PHOTOGRAPHIC CORRESPONDENCE.
[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.