DUFAY DIOPTICHROME PROCESS This employs a screen plate of French manu facture. A gelatinised glass is coated as to two thirds of its surface with a greasy material, which acts as a temporary resist, in the form of lines, points, or grains of geometric or irregular shape. The present plate consists of lines with rectangles in between. The bare parts are dyed and the whole surface varnished and treated with a solvent of the greasy material so as to lay bare the unstained gelatine. Half this surface is then again covered with a greasy substance, and the bare gelatine again dyed, again varnished, the greasy material again dissolved, and the last portion of the unstained gelatine dyed. A compensating filter is used, and the plate is issued with a special panchromatic plate fitting into a frame with nickel pins which allow of complete registration of the positive and colour screen. Coloured plates to this work show the formation of the Duf ay plate, and a typical result obtained with this plate.
The plates must be manipulated in absolute darkness or with the maker's special dark-room filter. The developer recommended is :
Metol . . . 53 grs. 6 g.
Sodium sulphite . . i oz. 72 Hydroquinone . . ty grs. 2 Potassium bromide . 17 2 ,, Liquor . 13o mitts. 15 ccs.
Distilled water to . 20 OZ. 1,000 For use, mix with an equal quantity of water and continue development for four minutes. Rinse the plate for some minutes, and immerse in Potassium or ammo nium bichromate 44 grs. 5 g.
Sulphuric acid . . 95 mins. to ccs.
Water to . . . 20 oz. i,000 When the image has dissolved, wash for several minutes till all the yellow tint has dis appeared, and immerse in the first developer or preferably in Metol . . . 22 grs. 2.5 g.
Sodium sulphite . t oz. so Hydroquinone . . 44 grs. 5 Potassium carbonate 220 25 Potassium bromide . 18 2 fl Distilled water to . 20 OZ. 1,000 ccs. Re-development takes about three minutes, and should be done in a bright light. The plate may be reduced with " hypo " and ferricyanide, and intensified with mercuric chloride followed by ammonia.