(A.) HUSNIK’S PHOTO-LITHOGRAPHIC PAPER.
Prof. Husnik has combined these two processes for the production of his papers, as he gives a coating of albumen to a paper coated with gelatine, which should be rendered sensitive with ammonium bichromate. By this means is, on the one hand, the rubbing up of the paper prevented and damage to the image not easily possible; on the other hand, the development takes place very quickly, as the albumen film dissolves and can be easily removed with the greasy ink. Husnik specially contends that with the use of these papers he obtains extraordinarily sharp images without any tint. The sheets thus prepared will only keep, however, one or two days, and this inconvenient operation has to be repeated every time before using the paper. This applies also to the albumen solution, so Husnik has come to the conclusion that it is better and more practical to use plain gelatine paper; but {54} when trouble, time, and cost are not of such great consideration, then it is better to use the paper with the compound coating, as it enables less experienced operators to produce good work.
The paper more recently produced by Husnik is a pure gelatine paper, which is rendered sensitive to light in—
| Ammonium bichromate | 1 | part |
| Water | 15 | parts |
| Alcohol (ordinary) | 4 | parts |
As much ammonia is added to the bichromate solution as will convert the reddish colour into yellow, and the bath smells of ammonia. The bathing of the paper must be done as quickly as possible, and the sheet should only be drawn through the solution. The exposure for this paper is from one to three minutes in the sun, or from ten to thirty minutes in diffused light.
The inking up of the print should be done with a greasy transfer ink, to which one-sixth part of wax has been added, and the whole dissolved in turpentine to the consistence of oil. The print is inked up with this thin ink, and then gone over with a pad of cotton wool till it has taken an even gray tint.
When the turpentine has evaporated the print is laid in cold water, and, after about ten minutes, developed with a soft thick pad with a continuous circular movement and quite light pressure. After development all adhering water is removed from the print with damp blotting-paper, and the transfer can be effected after from fifteen to twenty minutes.
Husnik, however, did not rest, and soon prepared a still better paper, which is known at the present time commercially as “Husnik’s Autotypic Paper.” He produces this paper in large quantities, the coating of the gelatine being effected by machines, which certainly tends to ensure equality.
Husnik found that by the use of less concentrated bichromate baths the fine lines were stronger after printing than from the nature of the negative they should be. From one and the same negative there was obtained by the use of a bichromate bath of 1 : 100 a relief five times as broad as when a bath of 1 : 15 was used to sensitize the paper. This he ascribes to the colour of the gelatine being less, so that more rays of light penetrated to the surface of the paper, from which it would be again reflected, and every point or line again reproduced, which must obviously lead to an increase of the size of the same; on the other hand, with strongly chromated paper, the rays of light would not only be absorbed by the intense yellow colour of the chromium salt, but still more by the brown tone formed immediately after printing, which makes a reflection impossible. With autotype negatives this is specially striking, as with weakly-chromated paper black shadows without details occur, because here the quantity of light is distributed by reflection over the fine points, and they will {55} therefore become thicker. When using strongly-chromated papers the details in the shadows appear open, clear, and sharp.
The concentration of the bichromate bath cannot be increased at will, because other disadvantages are produced, especially such a firm adherence of the greasy ink to the print that it transfers badly and a part of it always remains behind. The bichromate salt, when as strong as 1 : 18, dissolves the gelatine at ordinary temperatures, and the baths, neutralized with ammonia, have the disadvantage that the greasy ink adheres too little to the print and will be rubbed away in developing the drawing. In order to entirely obviate the reflection of the rays of light Husnik uses an addition to the gelatine besides a 1 : 22 acid bichromate bath, which produces a pure yellow tone in sensitizing the papers, is insoluble, and completely penetrates the film of gelatine, so that a reflection of the chemically active rays is entirely avoided.