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Screen-Plate Practice 523
V. Cremier05 recommended for extreme brilliancy for projection:
Metol . . 7 g.
Hydroquinon 8 g.
Sodium sulfite, anhydrous 100 g.
Ammonia, sp. gr. 0.923 32 ccs.
Potassium bromide 6 g.
Water 1000 ccs.
This is also very suitable for plates that have been hyper-sensitized.
Subjects of extreme contrast are difficult to deal with, even with ordinary plates, which have a very much greater latitude than all screen-plates. Drake-Brockman66 proposed the use of a preliminary bath of from 0.5 to 1.5 per cent of potassium dichromate, for times ranging from 1 to 2l/2 minutes, prior to development, then washing for 2 minutes. This was also recommended, especially for photomicrography, by O. Lederer.67 For extreme contrasts G. Balagny08 advised the use of acid amidol, with the addition of sodium sulfite in small quantities at a time, according to the appearance of the image.
A. J. Woolway09 recommended rodinal, 1 : 100, for 6 minutes at 15° C. This was also commended by E. Clifton,70 H. D'Arcy Power,71 and E. J. Steichen.72 R. Namias73 recommended glycin and sodium carbonate, without sulfite. A. Ebert74 recommended edinol.
The Reversing Solution. — The purpose of this is to dissolve the primary image, and that first recommended by MM. Lumiere was:
Potassium permanganate 2 g.
Sulfuric acid, cone 10 ccs.
Water 1000 ccs.
First dissolve the permanganate, then add the acid slowly with constant stirring. The solution should be kept in the dark, and should not be used a second time. It should be allowed to act for 3 or 4 minutes.
Unfortunately some trouble was caused from this, and it was found better to keep it in two solutions75 by dissolving the permanganate in half the water and the acid in the rest, and mix just before use. Stale solution is somewhat slow in action and may give rise to black specks, due to the precipitation of some insoluble manganese compound. This is particularly the case if the solutions have been kept in the light. To avoid this deposition H. D'Arcy Power70 suggested immersing the plate face down. G. E. Rawlins77 proposed the use of fresh solution, 5 to 10 per cent, of ammonium persulfate, followed by a weak bath of sodium bisulfite, about 3 per cent. The Comte de Dalmas78 proposed the use of a dry reverser, which was specially useful on tour as it merely required dissolving in water to be ready for use. The formula was:
Potassium permanganate 2 g.
Sodium bisulfate 50 g.
This quantity being sufficient for a liter.