Bromoil printing and bromoil transfer

by Emil Mayer

In the various kinds of multiple transfer here outlined principles have been introduced into the transfer process which have been used in the gum-bichromate process and many graphic reproduction processes, in order to produce wide ranges of tone values by several printings on one print. Yet the means of attaining this end are novel, namely, either different consistency of inks with one print-plate, or the use of two different print-plates for one transfer.

In my first publications on such combination transfer processes, I mentioned still a third possibility of obtaining the desired end, namely the preparation of two partial transfers from one print by using two different degrees of relief. The process first outlined, using different consistencies of ink with one print, is, however, to be preferred to the process in which two reliefs are used, wherefore the latter was not further proceeded with.

The value of the transfer process has been so increased by the methods just outlined that it is capable of solving the most difficult photographic problem, and by its aid even negatives can be printed, which cannot be satisfactorily rendered even in bromoil. While hitherto the transfer process was only an offshoot of the bromoil process it is, since the introduction of combination transfer, at least as valuable and in many cases even surpasses it.

CHAPTER VI
OIL vs. BROMOIL

Oil Printing and Bromoil Printing.—Oil printing and bromoil printing are frequently considered as two different photographic processes. From this premise different conclusions have been drawn, thus for instance, that oil printing is more suitable for certain subjects and that bromoil printing is to be preferred for other purposes. There has also been discussion as to which of the two processes deserves the preference, which produces the finer artistic effects, and so on.

All these discussions are, however, superfluous, for the assumptions on which they are based are erroneous. Oil printing and bromoil printing are actually not two essentially different techniques. In both cases there is one and the same process; oil and bromoil printing are basically identical. This can be proved both theoretically and practically.

The theoretical considerations are as follows: in most photographic processes the chemical property of certain substances of being changed by action of light is used for the production of the final image. Such photochemical processes only play a preparatory rôle in oil and bromoil printing. The production of the final image is here based on a physical property of the gelatine, namely on its innate possibility of being tanned or hardened. In oil and bromoil printing an image is first formed in the gelatine photochemically. This image is, however, not the final one; it is merely a means to an end. Its actual purpose is the attainment of a suitable tanning of the gelatine. The photochemically produced image is therefore removed, but in such a way that simultaneously with the elimination of the image, the gelatine which carried it is proportionately tanned in the lights and shadows of the picture. Only by this tanning is the gelatine made ready for the production of the final picture. The purpose of these preliminary steps is the production of the tanned image in the gelatine, which by itself is invisible or scarcely visible. After carrying out the preliminary processes the result is a pure gelatine film, which shows places of greater and lesser tanning corresponding to the photochemical image which has disappeared and which, therefore, has greater or lesser capacity for swelling in these places. If at this stage there are still chemicals in the film they are of no value for the further processes.

If a gelatine film thus prepared is swollen in water, the untanned places suck up water, while the tanned parts do not take it up. Fatty inks, applied with suitable brushes, are then repelled by those parts of the gelatine which hold the water, while the tanned parts of the film freely take the greasy ink. The final image, therefore, is not formed until the inking-up of the film with greasy inks.

This technique may, therefore, be most suitably characterized by the name “inking-up process.” The usual names oil print and bromoil print merely designate, although in terms which are terminologically unsatisfactory, two methods of preparing the base for the inking-up process.