This section is from the book "Complete Self-Instructing Library Of Practical Photography", by J. B. Schriever. Also available from Amazon: Complete Self-Instructing Library Of Practical Photography.
Introduction. Ozobrome may be described as a simplification of the carbon process. The result obtained is a true pigment or carbon print, produced by a chemical process instead of by the direct action of the light.
373. Any class of negatives may be used for making the print or enlargement, as the numerous grades of bromide and developing-out papers make it an easy matter to produce either soft or contrasty effects at will.
374. The use of enlargements does away with the trouble and expense of making enlarged negatives.
375. Ozobrome prints, with a choice of twelve colors, can be made either upon the original print or transferred to any suitable surface. The image is not reversed, making double transfer a thing of the past. A number of prints in Ozobrome can be made from one print without the use of a negative, and the original print may still be retained unimpaired.
Materials Required. A thoroughly fixed (in plain hypo), washed and dried print on bromide or developing-out paper, a sheet of Ozobrome Pigment Tissue (for method No. 2 provide also a sheet of Ozobrome Transfer Paper), and a package of Ozobrome Sensitizing Powder. Also provide a porcelain tray of proper size, for sensitizing (ordinary trays may be used for washing and fixing), a thermometer, a flat squeegee and a package of chemically pure blotters.
377. The print should be hardened by a five minute immersion in a ten per cent. solution of formalin, or for ten minutes in a four per cent. solution of chrome alum, washed twenty minutes, then dried. The hypo must be thoroughly eliminated from the prints to be used for this purpose.
378. Toned or redeveloped prints do not afford the best results. When the transfer process (No. 2) is to be employed, a good strong paper with a fairly smooth surface, should be selected, as the prints will have to undergo a little wear and tear.
Note. It is very necessary that the prints used for this process be fixed in plain hypo, as an acid bath will have a tendency to produce a flat print when finished.
The Non-Transfer Process. (No. 1.)
Working Instructions. In this process the original print forms the support of the picture and consequently can be used but once, but as it is much easier and quicker than the transfer process, it will be the one generally adopted.
Theory Of Process. In the carbon process the tissue is sensitized by the immersion in a solution of bichromate of potash, which, when dried and subjected to the influence of light passed through a negative, causes the gelatin of the tissue to become insoluble in the proportion to which it has been acted upon by the light. The action of light changes the bichromate of potash into a chromic salt, which has the property of rendering the gelatin insoluble. In Ozobrome, this change is not brought about by the action of light, but by a chemical action, thus doing away with the exposure of the tissue under a negative. Having provided the required materials, the method of procedure is as follows:
382. Provide an amber-colored bottle, holding twenty ounces; then dissolve the contents of one tube of Ozobrome Sensitizing Powder in 20 ounces of water. "When dissolved pour into the amber bottle and see that it is well stoppered. This solution will keep in good condition for about 48 hours. The sensitizing solution is to be used as described in the following instruction. Having at hand the print and sheet of pigment tissue of the desired color, proceed as follows:
MOTHER AND CHILD. Study No. 7-See Page 356 Mrs. Nancy Ford Cones.
383. Pour into a porcelain tray of proper size the required amount of sensitizing solution (about 10 ounces for a 10 x 12 tray) which is adequate for two sheets of the pigment tissue. If the tissue curls before immersing in the solution, bring the back of the tissue in contact with the solution, unrolling it gently until the entire surface of both sides is wet. The tissue will soon straighten out and in three minutes become perfectly limp and should then be removed from the solution. Care should be exercised to prevent the formation of air-bells on cither side of the tissue, while immersed in the sensitizing bath. The bath should be discarded after two pieces of the tissue have been immersed.