Diamidophenol . . . . - • • gr.
Metabisulphite of Potash . . . . •i oz.
Sodium Sulphite . . . . . . 2 „ Water . . . . • . • • • 20 ol Or it may be substituted for amidol in the previous formula.
Ortol.—A composite developer introduced by Dr. Hauff, which consists of a mixture of hydroquinone with methyl ortho-amido-phenol. It acts in a very similar way to pyro but is stainless; the negative produced is somewhat less dense.
A. Ortol . . . . . . . . 7o gr.
Potassium Metabisulphite . . . . . • 35 „ Water to oz.
B. Sodium Carbonate . t oz.
Potassium Bromide . . . . • • • 5 gr. Sodium Sulphite Water Pyrocateckin developing agent, first introduced by M. Benoist, is the same in its components as hydroquinone, but behaves very differently. It acts energeti cally at a low temperature, giving a brown, fairly printing negative. On the other hand it is equally useful in hot weather, as the tanning action which it exercises upon the gelatine diminishes the risk of blisters and frilling in the film. The formula given for pyro soda will serve for pyrocatechin with the addition of more water, if required.
A. Pyrocatechin . . . . • . . . oz. Sodium Sulphite„ . . . . . .
Water zo B. Sodium Carbonate . . . I oz.
Water to The acid fixing bath is said to be unsuitable for negatives developed with liyrocatechin.
Eikonogen is not very widely used for plates, but gives clear negatives, full of detail without great density in the high lights, and therefore suitable when bromide enlargements are needed rather than direct printing.
A. Eikonogen . . . . . . . . . So gr.
Sodium Sulphite . . . . . . t6o „ Water B. Sodium Carbonate . . . . . . t oz.
Water . . . . . . . . . to „Eikonogen is often used in conjunction with hydroquinone, the presence of the latter increasing vigour and contrast. The following formula we have used with great success and especially for the development of Kodak films : A. Sodium Sulphite Eikonogen . . . . . . . . . t8o gr.
Hydroquinone . . . . . . . . 120 „ Water . , . . . . . zo oz.
B. Potassium Carbonate Water. . . . . . 20 „ • •Take A t part, B 2 parts.
Kachin.—The chief recommendation of this developer its cleanliness and its success for the development of stale plates, on which it does not produce the usual iridescent markings.
A. Kachin . . . . . . . . . I oz.
Sodium Sulphite . . . . . .t „ Citric Acid . . . . . . . . zo gr.
Water . . . . . . . . . to oz.
B. Sodium Carbonate . . . • . . . 36o gr.
Water . . . . . . . . . to oz.
For use take t part of A and t part of B, with from one to two parts of water according to the nature of the exposure. No bromide is required.
There are many other developers of this kind. We may mention adurol, the action of which is very similar to hydro quinone ; edinol, sometimes recommended as a clean substitute for pyro and equal to it in range of densities ; glycin, slow in action, but very sure and specially adapted for tank develop ment ; azol, synthol, imogen sulphite, diphenol, etc., etc.
Those who wish to experiment will find suitable formula-2 provided in the ounce packages supplied by the manu facturers.
Ferrous Oxalate, once a great favourite, is now very little used for plates. It gives a very brilliant, sparkling negative, but the resulting prints have often a deadly dull look on most modern papers. The old formula was : A. Saturated solution of Ferrous Sulphate.
B. Saturated solution of Potassium Oxalate.
Take I part of A and 3 parts of B.
Before fixing the plate must pass through three changes of water, to which a few drops of citric-acid solution have been added to remove the otherwise insoluble iron salt. From the peculiarity of its chemical reaction ferrous oxalate is the one chosen for standard tests. We subjoin the formula used by Messrs. Hurter and Driffield : A. Potassium oxalate . . . . i part Water . 4 parts B. Ferrous Sulphate . . . . . . t part Citric Acid . . . . . . . o•or part Water . . 3 parts C Potassium Bromide . . . i part Water . . . . . . . . too parts For use, take A wo parts, B 25 parts, C io parts.
Daylight the British Journal of Photo graphy, August 27, 1909, a method was described for desen sitising plates after exposure by immersion for a minute or two in a 4 per cent. solution of potassium iodide. They may then be brought out into daylight and developed in a metol hydroquinone developer fully restrained with bromide. As an interesting experiment 'at the lecture table the process may have its value. But the results will not bear very critical examination, although the solution is said to be sold for the purpo$e in Germany.
We do not know whether the following combined developing and fixing bath for daylight use, described in the same journal, is permissible by the patent laws. Picrate of soda or of magnesia forms the colouring agent, the first-named being the more soluble.
Magnesium Picrate . . . . . . 81 parts Sodium Sulphite (anhydrous) . . . . 544 parts Sodium Hyposulphite (hypo) . . . . zso parts Diamidophenol . . . . . . . parts This powdered mixture is dissolved in water to the extent of about zo gr. per ounce, and the exposed plate or print having been placed in it in the dark, the further operation may be continued in daylight or other actinic light. The credit of the proposal is due to MM. F. Jeannot and M. R. Bremner.