This is a modification of the ordinary oil process, and is a revival of an old method of making photolithographic transfers, first introduced by Sir \Y. Abney. There is no great difficulty in the actual printing and development, in fact it is much easier, and requires much less manual skill than oil printing as generally understood. For the amateur it has this drawback, that the paper must be manufactured at home; it has proved to be so perishable, even before sensitising, that it cannot be stocked as an article of commerce.
A cartridge or drawing paper is floated on a bath consisting of:
Gelatine (Nelson's Flake)...... 8 oz.
Glycerine . . . . . . . . 1 1/2 „
Common Salt........ 2 ,,
Water.......... 50 „
Soak the gelatine for twelve hours, then melt under heat, but do not raise the temperature much above the point at which the gelatine is dissolved. Avoid getting bubbles on the surface of the paper. Dry the paper at a temperature of 85-900, and afterwards keep in a dry atmosphere. Not more should be made at one time than will be wanted for use during the next two months. Sensitise as follows:
Potassium Bichromate......1 oz.
Common Salt ....... 1/2 ,,
Potassium Ferricyanide . . . . . . 120 gr.
Methylated Spirit.......5 oz.
Water ................................... 25 „ and squeegee on a ferrotype under blotting-paper, or dry at a temperature of 80° - of course in some place secure from actinic light.
Operations will be simplified considerably, if a piece of paper much larger than the negative is used for the print, allowing of a "safe edge" about a inch and a half all round the picture. The negative may be put under plate glass in a large printing frame, and this edge protected by a mask of black paper. Printing is soon accomplished; the image will print out a brown or even chocolate colour upon the yellow ground. When this is attained remove the print and let it soak in cold water for ten minutes; next it may be transferred to lukewarm water 800-90° or, if very bright prints are required, at still higher temperature; but care must be taken not to expose the gelatine to a heat which will cause any part of it to leave the paper support. When the grain appears sufficiently coarse (which can be ascertained by lifting from the water and blotting off some portion) lay the print on a glass plate and blot off superfluous moisture.
Meanwhile a small quantity of lithographic ink, or oil colour with copal oil and a drop or two of varnish has been deposited on a dry glass plate to serve as inking slab. Mix with a palette knife two or three small dabs of oil colour or ink about the size of a pea on the inking slab, pour on a little turpentine to thin the mixture, and distribute the ink evenly well over the slab by means of a gelatine roller, such as is used in the printing trade. As the turpentine evaporates, the ink on the slab will assume a velvety soft appearance, and respond with a characteristic tacky sound to the action of the roller backwards and forwards. It is then ready for use.
The roller, duly charged with ink, is now rolled with a steady even motion backwards and forwards over the gelatine print, upon which it will leave a film of ink - at first over the whole picture impartially, but the high lights will gradually whiten. Do not use too much ink, but feed the roller with fresh ink if the image is too pale in colour. Slow rolling deposits ink upon the image; faster rolling clears the picture. A very little practice will make perfect in the mysteries of inking up.
When the papyrotint is satisfactory, soak for a minute or two in an alum or formaline bath, and hang up to dry.
The conversion of a bromide print into an oil print. Glossy-surfaced prints are not often successful, and the print should be of recent development. It is first bleached in a solution compounded very much as follows:
Potassium Ferricyanide . . . . . . 4 gr.
Potassium Bromide.......18 ,,
Potassium Bichromate......18 ,,
Alum Ammonia........36 „
Hydrochloric Acid . . . . . . . 60 ,,
Water....., . . . 4 oz.
We give this formula of Mr. A. H. Garner's, in order to show the chemical reaction.
It has been claimed, however, that the above is a breach of Mr. T. Manly's patent, and it would perhaps be better to use the following variation, as no one should begrudge this gentleman the lawful reward of his investigations:
Ozobrome solution....... 4 oz.
Potash Alum 10% solution...... 4 „
Citric Acid 10% ...... 1 „
Water.......... 20 „ after which it is soaked in a 5 per cent. solution of sulphuric acid until the high lights of the picture appear in relief, which will generally happen within five minutes. The image is then fixed out in an ordinary fixing bath, but this is not absolutely necessary, unless the pigments to be employed are of so light a colour that the silver when darkening would spoil the effect. In summer the image will occasionally show itself in relief without the use of the acid bath.
After washing, the bleached print is ready for pigmenting, which is done in much the same way as with ordinary oil prints, or even with the roller employed for papyrotints.
Ordinary Robertson's medium may be mixed with tube colour and dabbed, smudged, or "hopped" on with the usual smooth brush, or with a soft muslin or cotton-wool dabber according to the skill of the particular artist. With finer brushes it is not difficult to touch in light effects in colour. The bromide image remains in faint yellow as a guide, and we have seen some excellent bromoils of spring flowers and the like subjects of not too complicated nature executed in two or three colours.
If any mistake is made and the effect is unhappy we can wipe the picture off with a little benzole, wash in water, and start afresh, so long as no ink has been allowed to get at the paper on the back of the print. Elaborate directions as to the laying on of the oil pigment, of devices for increasing light and shade, and of other instruments which may be enlisted into service, we are not called upon to append here. Bromoil, like gum-bichromate, is an art process, and one which affords the individual worker an opportunity to mature devices for himself and to apply them in his own way. A little practice, and perhaps a few spoilt prints, are not a heavy price to pay, if the experience gained eventuates in productions combining success with the higher quality of originality.
Manufacturers are beginning to label the bromide papers most suitable for conversion into bromoils. IIford rough, llford, or Wellington carbon; Barnet ordinary or rough present little difficulty. The latest advice can generally be obtained when purchasing the ozobrome solution from the Ozotype Company, who from time to time publish new directions for the more economical management of the process. A simplified bleaching bath lately suggested by the company consists of:
Ozobrome solution ....... I part.
Hydrochloric Acid (pure) 1 per cent. solution . . 5 parts Water.........4".
To make up the hydrochloric acid solution take 2 drams fluid (sp. gr. 1.16) to 25 oz. water. In one to three minutes the print will become a faint yellow colour and may then be placed direct into the fixing bath:
Hypo.......... 2 oz.
Ammonia......... 1 dr.
Where it must remain from two to six minutes according to the original hardness of the bromide emulsion, which can be gauged with sufficient accuracy by the time the image takes to bleach. After a wash of three to five minutes it is ready for inking up.
According to experts, the bromide prints which make the most successful bromoils are those developed with amidol, or hydroquinone combined with metol.