Alternative Bleach for Sulphide Toning.—Bleach the print in Ammonium Bromide . . . 5o gr.
Potassium Ferricyanide . . . . . 150 „ Water . . . . . . . 10 oz.
Wash well in several changes of water, and then tone to tint desired in a solution of pure sodium sulphide 15 gr. to the ounce of water.
Platinunz Toning.—Bromide prints (but not gaslight prints as a rule) may be toned in a solution of platinum perchloride. They lose density to a considerable degree while under treatment, and must therefore be allowed to over-develop. The colour will vary according to the propor tions of platinum salt and acid in the toning bath. For sepia tones : Platinum Perchloride . . . . . . 2 gr.
Hydrochloric Acid . . . . . . 6o min.
Water , to oz.
Gaslight Papers.—A series of new papers, known under such names as " Velox," " Gravura," " Slow Contact Paper," etc., etc., have been gradually taking the place of bromide paper for contact printing by artificial light. The principle of most of these is an emulsion consisting chiefly of the chloride and other salts of silver which are scarcely sensitive to any rays of light except those between F and H on the spectrum, viz. the blue and violet. They are nearly all white in colour, and not of creamy tint like the bromide papers. These papers therefore do not need the use of a dark room, and may be manipulated within a few feet of the gas-burner by which the picture is printed, such light being comparatively poor in blue and violet rays. The most convenient arrangement is to shelter the developing dish behind a large sheet of cardboard or other light screen on the table, say, six feet from the source of light.
There are many ways of working these papers, and it is not easy to give directions that will apply alike to all the brands that have attained to popularity. Some photo graphers prefer to give a very long exposure to light—two or three minutes—and develop in the much-diluted formulae adopted for bromide papers. By this means it is possible to secure very great softness of detail, and also a range of colours from light brown to rich chocolate, black, and even blue. The more common practice is to expose for a shorter time and use a stronger developer.
Development.—The development of gaslight papers is much the same as for bromides, except that the developer must not be poured off the print until it is ready to be transferred to the fixing bath ; the developer will oxidise in the paper if exposed to the air. Development is often
complete within a minute, when the liquid must be poured off and the picture very quickly rinsed in water. The developer must always contain a small proportion of bromide solution. Two typical formula are given, the first that for the Ilford, the second for the Gevaert gaslight papers.
(I) Metol . . . . . . . 5 gr.
Sodium Sulphite . . . . . . . 2 oz.
Hydroquinone . . . . . . . zo gr.
Sodium Carbonate (crystals) . . . . oz.
to per cent, solution Potassium Bromide . . . to min.
Water . . . . . . . . . to oz.
(2) For warm tones. The time of exposure may be pro longed or curtailed, in order to obtain a range of colours.
Glycin . . . . . . . . . . I oz.
Sodium Sulphite . . . . . . z „ Potassium Carbonate . . . . . • 5 t, Water, distilled and hot . . . . , 4 „ Dissolve the sodium sulphite first, then add the glycin, and lastly the potassium carbonate in small quantities as the mixture froths up. A 2o-oz. measure should be used for the above quantities. The result is a liquid of creamy appearance and consistency, which must be shaken before use. To develop take Stock solution . . . . . . . . oz.
Water Potassium Bromide (to per cent solution) . . 7 drops.
Rodinal is also a favourite developer with gaslight papers in the proportions of I to 30 or so.
Phosphate Papers.—Thesc papers, while produced and completed with a rapidity greater than the ordinary gaslight papers, have all the appearance of gold toned P.O.P.
" Ensyna," the earliest of these, can be finished off ready for drying and mounting in about six minutes, divided as follows : Exposure . . . . . . . about 3o sec.
Water bath. . . . . . t min.
Development . . . . . . . z „ Fixing 3o sec.
Washing . . . . . . . . . 2 min.
The film is very soluble, hence the short time allowed for fixing and subsequent washing.' The tones may vary according to length of exposure from engraving red, brown and sepia to blue-black ; over-exposure merely imparts a warmer tone to the print.
The Paget Phosphate Paper is developed with an acid metol developer, the proportions of which are varied to increase contrast or to alter the tones which may range from blue-black to purple and sepia. The prints undergo no alteration of tone in fixing, which is rapidly completed, and the last washing need not occupy more than half an hour. When fully exposed, the tones are similar in appearance to those produced by toning P.O.P. with gold.