By C. H. HEWITT, F.R.P.S.
Christened by Mr. F. J. Mortimer, one of its ablest exponents, Bromoil is, as one would surmise, a combination of bromide printing with the oil pigment process. In the Rawlins' process of oil pigment printing, paper coated with bichromated gelatine is exposed through a negative, the varying degrees of light action producing varying degrees of insolubility. As the temperature of the soaking water is not raised very high, the gelatine does not dissolve, but merely swells, a good deal in the unexposed portions, less in the half-tones and very little or not at all in the deep shadows. This unequally swollen gelatine image is pigmented with a somewhat stiff greasy ink, the pigment adhering most where the gelatine has swelled least.
In Bromoil, an exactly similar condition of gelatine film must be produced; but this is done by the application of two or three solutions only and without the necessity of daylight for printing. The reduction of the potassium bichromate necessary to produce the insolubilizing of the gelatine, which in the oil process is due to light action, is, in Bromoil, obtained by chemical means.
Before going into the details of the methods, it may be well to point out one or two advantages the process enjoys. Neither oil nor Bromoil printing will be used to any extent for small direct negatives such as the majority of workers obtain with the almost universal small camera. While the Bromoil process only requires a Bromide print or enlargement, the oil process usually necessitates the making of an enlarged negative, for the negative must be the same size as the print desired.
C. H. Hewitt.
By Furley Lewis.
* Abridged from " The Oil and Bromoil Process " issued by the Publishers.
Such an enlarged negative may not be difficult to make, but positive, negative, and print, it must be admitted, is a lengthier and more troublesome way than a print direct, and a print made by projection in the lantern is as easily produced as by contact in the printing frame. There is, further, the obvious question of cost. A 15 X 12 plate represents one and sixpence as against a trifle over sixpence for a sheet of bromide paper, and this ignores the few pence for the sheet of oil printing paper.
In the oil process there are certain difficulties which occur when dealing with the chromic salts in conjunction with gelatine. The paper must be freshly sensitized, and precautions must be taken against damp and faint light fog. The printing of the sensitive paper needs to be carried to the exact point with considerable nicety ; with Bromoil, a good, clean bromide print of average strength is required, and this one can be certain of having before the work of preparation and pigmenting is commenced.
THE BROMIDE PRINT.
Little need be said with regard to the preparation of the bromide print. Care must be taken in handling the paper to avoid finger markings and also creasing and kinking, which, under certain conditions would be likely to induce blistering. The print must be developed fully with the amidol or the metol-hydrokinone developer, and it must be well fixed and well washed and should, preferably, be dried before further treatment. It will be found that the better the bromide print the better will be the resultant bromoil, and the easier and more straightforward the operation of pigmenting. Poor, weak and washed-out bromides will not yield good bromoils, and my own experience is that the bromide print needs to be rather on the dark side if the older type of bleacher is used. With the Sinclair Bleacher, to which I refer later, a normal print will work perfectly.
As to the choice of paper it may be necessary to say something. Most of the ordinary papers (in contradistinction to the platino-matt) are excellent, pigmenting readily and withstanding quite as much brush action as should ever be required. Experiments have shown their ability to withstand a sufficient amount of " hopping " even if a hog-hair brush is used.
If the temperature should be so high that the gelatine becomes too swollen and soft, the use of ice may be resorted to, and I have found that a small piece in each of the solutions, with a larger piece in the dish in which the print is rinsed between the various baths, is a satisfactory plan, the very slight weakening in strength of the solutions being unimportant.