Since the introduction of the new process into the United States, the preparation of rapid dry plates has been and remains now in the hands of certain prominent firms, who, from the skill they have acquired and the advantages they derive from all the machinery and conveniences that large capital enables them to procure, are enabled to supply fully the demand with a much better article than could be had were each consumer to manufacture for himself. In fact, if the photographer were compelled to manufacture his own dry plates there would be a very different condition of affairs at the present time.
Gelatine is a substance so susceptible to change from the action of our climate, with its varying temperature, that of a large number who have attempted to make dry plates for the trade, many have completely failed, some of them after a partial success; and others after spending thousands of dollars never could make two batches of emulsion alike; and then again the keen competition of the successful concerns has reduced the profits to not more than fair returns to a precarious business.
There are many, no doubt, who would be glad to experiment in this field, especially among amateurs, and it is for the benefit of such that certain hints and formulæ are given in this connection to enable them to make, if successful, their own plates.
The formulæ herewith given are selected from a large number published in the German, English and American journals, and while good dry plates may be made by either of them, yet it is doubtful if the highest success would repay the outlay. [p039]
A careful study of the published formulæ and the current literature on the subject of Gelatino-Bromide Emulsion will disclose the general principles on which they are based.
A certain amount of bromide of ammonium or potassium (preferably ammonium, on account of its greater uniformity and purity) and nitrate of silver are dissolved separately, and mixed together in a thin solution of gelatine, at a moderately warm temperature. Great sensitiveness is obtained by a long exposure to the same warm temperature, or by the addition of a small amount of ammonia, and raising the heat to the boiling-point for from a half to a full hour; when it is cooled more gelatine is added and the whole allowed to congeal or set, when it is reduced to shreds, and washed in cold water to remove the excess of the preponderate salt.