The advance of photography : its history and modern applications (1911)

PHOTOGRAPHY IN NATURAL COLOURS 255 complete darkness : — Opening the boxes, putting the plate into the dark slide, the first development, and the washing and immersion in the dissolving bath. The plates should be placed in the dark slide, as has already been described for the autochrome plates. A special colour filter must also be used with the plates, and it might be pointed out in this connection that it is essential that in all cases these colour screens should be suited to the plates for which they are intended. Many of the cases of failure in which a false tint can be seen to dominate the whole photograph are due to the fact that an unsuitable screen (filter) has been used. The screen can be used with these plates either in front of or behind the lens, the focussing screen being arranged with its rough side outwards. The exposure required with these plates is much longer than for ordinary plates ; thus a well-lighted object requires from one to two seconds when using a lens working at //8 in the middle of a summer day. The following method of treating the exposed plates is recommended by the makers. The stock solution for the first development contains : — Distilled water . . 1000 c.c. Metol .... 4 gms. Anhydrous sodium sulphite 50 gms. [or double quantity of crystallized] Hydro quinone . . 2 gms. Anhydrous potassium carbonate ... 30 gms. Potassium bromide . 1 gm. 1 per cent, solution of sodium hypo-sulphite . 15 c.c. 100 to 150 c.c. of this solution should be in readiness in the developing dish ; the room should then be made totally dark, and the plate taken out of the camera, its film care