When it was announced in England that Welborne Piper had discovered a process which started from a finished silver bromide print instead of from a gelatine film sensitized with bichromate, new vistas were opened. If the process should prove to be practically useful, we could consider that all the previously mentioned difficulties were overcome at a single stroke.
The principle of this process, bromoil printing, is the removal of the silver image from a finished silver bromide print by means of a bleaching solution while, simultaneously with the solution of the silver image, the gelatine film is tanned in such a way in relation to the previously present image that the portions of gelatine which represent the high lights of the image preserve their capability of swelling, while the shadows of the image are tanned.
Therefore the bromoil process is a modification of oil printing, based not upon a bichromated gelatine film, but upon a completed bromide print. This represents extraordinary progress. The two previously mentioned disadvantages of oil printing are completely avoided in the bromoil process. We now have at our command the far longer scale of tone values of bromide paper and we can use the great possibilities of modification allowed by the highly developed bromide process. The difficulties of printing are completely removed, for we have at our command a perfectly visible image as a starting point. A further advantage which can not be too highly estimated is inherent in the bromoil process: complete independence of the size of the original negative.
When I began my investigations in the field of bromoil printing, the process had, as far as practical value went, only a purely theoretical existence, as is the case in the early days of most photographic processes. The fact that it was possible to produce images on a bleached bromide print by the application of greasy inks was well established. The practical application of the process was absolutely uncertain and only occasionally were satisfactory results obtained. Most of the prints produced in this way were flat and muddy. It is easy to understand that the process could find no widespread popularity while it was so incompletely worked out. The researches, which I then began, showed that most bromide papers took up greasy inks after development by any method and subsequent bleaching of the image. The pictures thus obtained, however, were muddy, flat, and not amenable to control, and therefore were less satisfactory than the bromide prints from which I had started. During the course of my work, I have succeeded in obviating these difficulties, in the first place, by preparing a satisfactory bleaching solution, next, by determining what properties bromide paper must possess in order to give perfect bromoil prints, and, finally, by working out a series of other necessary conditions, which I have described in this book and which must be adhered to if the process is to work smoothly and certainly, and produce satisfactory results.
The bromoil process, which is now completely mastered, offers, in brief, the following advantages:
Simplicity, certainty and controllability of the printing material;
Independence of the size of the negative and easy production of enlarged artistic prints;
Freedom in the choice of basic stock and its surface;