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.
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.
H. P.
21. Maddox Street, Regent Street.
Test for Lenses.—In applying the methods recommended in your last Number for the purpose of testing lenses, there is one precaution absolutely necessary to be taken, but which all your correspondents have omitted to point out. The operator must take care that his focussing-glass is placed at precisely the same distance from the lens as the collodionised glass is. To insure this, my practice is to place a piece of ground glass in the dark frame, which is afterwards to receive the collodionised glass, and to obtain the focus of the lens on that; then to put in the proposed plate, and obtain an impression as described by Mr. Shadbolt. In this way I secure myself from what I believe is often a source of fallacy in these experiments, and am sure that I give the lens a fair trial.
E. S.
Washing Collodion Pictures.—I have never offered to your readers an opinion in photography without having bonâ fide tested it, to the best of my ability; and however correct my friend Mr. Shadbolt may be, chemically and theoretically, I am convinced that in practice so good a tone is never obtained in a positive collodion picture which has been washed, as in one which has been instantly fixed with the old saturated solution of hyposulphite of soda. The unpleasant tints obtained upon positive collodion pictures, I believe to be much dependent upon the frequent washings in the proofs. When a collodion picture is properly treated, it surpasses in pleasing effect every other photograph.
H. W. Diamond.