First Preparation Of The Plates. Take twenty - five parts of white of egg, forty-five parts of distilled water, and eight parts of solution of soda water-glass, such as can be obtained in commerce. The white of egg must be perfectly free from the yolk. The three constituent- are mixed together, beaten to a froth, and then allowed to stand, Next day, or at any rate after an interval of six or eight hours, the char portion is decanted off and altered through a clean cloth. This will render subsequent filtration through a paper much easier. An open glass vessel, or glass beaker, is taken, and a glass funnel is put into it, so that the tube of the latter reaches nearly to the bottom; the filter is then
357. In the preparation of the sensitive films, a first liquid should be made as follows:
Albumen (fresh eggs),
(4 " 7 " )
Bichromate of Potash,
( 1dr. )
The alkaline bichromate, reduced to powder in a porcelain or glass mortar and added to the mixture of water and ammonia, rapidly dissolves in it; the albumen is then poured in, this last having previously been whipped to a froth, allowed to rest, and filtered with care. This liquid passes quickly through filtering paper. The mixture may be used until exhausted, but should not be kept for too long a time. The albumen would lose its solidity, even after having been strongly coagulated by the bichromate of potash, under the action of the light. - Leon Vidal. The following is a good substratum:
Bichromate of Ammonium,
Add the bichromate and beat all to a froth, and let it stand over night, and then neutralise the acid bichromate with a few drops of ammonia, and filter several times. Apply with a fitted with soft and thick filter-paper, and the mixture poured in. The pores of the paper are very speedily stopped, and the process of filtering is suspended; for this reason the solution is poured from the funnel back again into the glass vessel, the filter-paper is replaced by new, and the solution again passed through it. This operation will have to be repeated several times before all the liquid in the vessel has gone through the filter. "When the liquid has been once filtered, it can be easily submitted to a second operation without the filter-paper being changed. For this reason the filtered liquid is poured into another glass and filtered a second time. As the first filtrate always contains a few hairs or fibres, the liquid that passes through first of all should always be poured back to go through the filter again, and in this way a perfectly clean liquid, free from bubbles, is obtained. To prepare the plates a sheet of glass of large size is laid down horizontally, and on it is placed one of the mat plates, which has, first of all, been dusted with a brush. Upon its surface, and near the brush, and dry by slow heat or spontaneously, and expose the glass side to the light on a black cloth till a piece of silvered paper turns black; then put in the dark, for use when wanted. Or this substitute may be used:
Silicate of Soda,.........................
Bichromate of Potash,.........................
To the prepared albumen, two ounces, add five ounces of water. Now add five ounces of water to the silicate of soda, and mix them, pouring the soda into the albumen, stirring slowly all the time. Now add the gelatin and bichromate of potash to the remaining ten ounces of water, and dissolve by heat in a water-bath, being careful not to raise the heat above 120°. Then add the albumen and soda, mixing thoroughly. Filter, and flow the plates, and set away to dry spontaneously, free from dust. When about to use, immerse the plate in a dish of water about five minutes, then rinse and dry. Now place in the oven and heat to 100°; then take the plate on the spread left hand and coat with No. 2. - Artotyper.
The method of filtering the albumen by the Artotype Company is to tie a piece of clean chamois skin over the top of a funnel; after moistening with pure water, the albumen is carefully poured upon it; after filtration, the bichromate of potash is added, which may first be dissolved in a small amount of water. The less water in the substratum, the less liable to blister when it comes to be printed; only enough ammonia is used to preserve the albumen, and need not be used when the solution is used immediately. A piece of polished French plate - glass is carefully cleaned, as carefully as for making a negative; a perfectly clean flat brush, about three inches wide, is dipped.in the solution, the surplus albumen removed by drawing once or twice over the edge of the dish. Now balancing the glass on the thumb and forefingers of the left hand, draw the brush containing the albumen diagonally across edge, is poured some of the solution above described, and this spread over the plate by gently inclining it. Those parts are not wetted in this way are aferwards covered with the liquid by spreading it with a strip of paper; but, in any case, the liquid must not be allowed to flow quickly, bat gently in a line downwards. Another vend is brought to one corner of the plate, and there the glass is quickly turned on and, so that the superfluous matter runs off. The quick withdrawal of the liquid carries away any air-bubbles which may have formed when the fluid was spread with the paper; but if any should yet remain, a little more of the filtered solution is applied, and then again rapidly drained into the second vessel. The plate is permitted to drain, and is set up against the wall to dry. The fluid which has been poured off the plate must be filtered again before use. In this way a large number of plates may be prepared, and. in this condition, may be kept for six months. They must never be used immediately, but should remain a day or two before being employed. The longer they are allowed to remain, the better they are.
the plate, commencing at the upper right - hand corner, then diagonally across the plate in the opposite direction, after which the operation is repeated, going both ways square across the plate. The plate is next placed in the drying-oven, which is kept at an even temperature of about one hundred and thirty - five degrees; from twenty to thirty minutes are required to dry the plate. After the substratum is dry, the plate is placed with its albumen side down upon a board covered over with black cloth, and exposed to a diffused light until a piece of silvered paper placed by its side is pretty well blackened, when the plate is removed to the coating-room and solution No. 2 is applied. To apply solution No. 2, first have the plate warmed to the temperature of the drying-box, then holding the plate with the left hand, the same way as No. 1, pour upon and entirely across the upper end of the plate just enough of the bichromate solution to cover the plate, then slightly tilting it with the flat side of the little finger cause the gelatin to flow evenly the whole length, then drawing the little finger around the edges of the plate, cause the solution to flow to the edges all around. If there is a surplus gathered at the lower corner, turn it off the plate, and place the plate in the drying-oven to dry, which will take at least half an hour. Solution No. 8 consists of bichromate of ammonia, gelatin (same as in No. 2), chrome - alum, glycerin, and water. It contains about as much bichromate as in the preceding solution. The chrome - alum is to harden or toughen the film, and the glycerin to keep it from becoming too brittle; only a trace of glycerin is used. This solution is made and used the same as No.2, only in coating the plate the solution is poured upon the opposite end, so as to equal-ize the thickness of the coating. When again dry, the plate is placed in the printing-frame and printed in the usual way, and the progress of the printing examined from the back; experience will soon tell when they are sufficiently printed. They are then placed in running water of from seventy to one hundred degrees temperature, and left until all traces of the bichromate is washed out; when, after being again dried, they are wet up and put in the press and printed from. - " Air Old Subscriber " in the Philadelphia Photographer. 21