Read before the Birmingham Photographic Society. Reported in the Photo. News
EXPERIMENTS IN TONING GELATINO-CHLORIDE PAPER.
From the Photographic News we take the following: The use of paper coated with a gelatino-citro-chloride emulsion in place of albumenized paper appears to be becoming daily more common. Successful toning has generally been the difficulty with such paper, the alkaline baths commonly in use with albumenized having proved unsuitable for toning this paper. On the whole, the bath that has given the best results is one containing, in addition to gold, a small quantity of hypo and a considerable quantity of sulphocyanide of ammonium. Such a bath tones very rapidly, and gives most pleasing colors. It appears, moreover, to be impossible to overtone the citro-chloro emulsion paper with it in the sense that it is possible to overtone prints on albumenized paper with the ordinary alkaline bath. That is to say, it is impossible to produce a slaty gray image. The result of prolonged toning is merely an image of an engraving black color. Of this, however, we shall say more hereafter. We wish first of all to refer to an elaborate series of experiments by Lionel Clark on the effects of various toning baths used with the gelatino-citro-chloride paper.
The results of these experiments we have before us at the time of writing, and we may at once say that, from the manner in which the experiments have been carried out and in which the results have been tabulated, Lionel Clark's work forms a very useful contribution to our photographic knowledge, and a contribution that will become more and more useful, the longer the results of the experiments are kept. A number of small prints have been prepared. Of these several—in most cases, three—have been toned by a certain bath, and each print has been torn in two. One-half has been treated with bichloride of mercury, so as to bleach such portion of the image as is of silver, and finally the prints—the two halves of each being brought close together—have been mounted in groups, each group containing all the prints toned by a certain formula, with full information tabulated.
The only improvement we could suggest in the arrangement is that all the prints should have been from the same negative, or from only three negatives, so that we should have prints from the same negatives in every group, and should the better be able to compare the results of the toning baths. Probably, however, the indifferent light of the present season of the year made it difficult to get a sufficiency of prints from one negative.
The following is a description of the toning baths used and of the appearance of the prints. We refer, in the mean time, only to those halves that have not been treated with bichloride of mercury.
1.——Gold chloride (AuCl₃).............. 1 gr.
Sulphocyanide of potassium......... 10 gr.
Hyposulphite of soda............... ½ gr.
Water.............................. 2 oz.
The prints are of a brilliant purple or violet color.