Development and Developers
Hydroquinone-acetone Developer (slow).
Hydroquinone ... ... 150 grs.
Dry sulphite of soda ... 500 ..
Acetone ... ... ... 500 mins. (1 fl. oz. and 20 m.).
Water ... ... ... 10 ozs.
Formaldehyde (formalin) may be used in a similar way to acetone, but is not recommended.
Protection of a Stock or Made-up Developer from the Air. See Atmospheric Action.
Development after Fixation. It has long been known that in many instances an image may be developed on a plate which has first been fixed with "hypo," so that the film is clear like glass ; but it is only recently that much attention has been given to this subject. Dr. Neuhauss (The Amateur Photographer, Sept. 23rd, 1898, p. 754) says that one merit of the method is the great latitude of exposure which it allows, sixty times the. normal exposure being harmless. All that is required is to expose sufficiently, fix on the spot (in the dark room), and to wash thoroughly. The clear plates which bear the invisible image may now be fully exposed to light, and the development may be postponed for any length of time. The development is in full daylight, as follows: - A stock solution is made up with
Distilled water ............ 100 millilitres.
Sulphocyanite of ammonium "' ... 24 grammes. Nitrate of silver ... ... ... ... 4 ..
Sulphite of soda ... ••: ... ... 24 ..
Hyposulphite of soda ...... ... 5 ..
10 per cent, bromide of potassium
solution............... 6 drops.
This stock solution keeps well, and for use 6 c.c. of it are mixed with 54 c.c. of water and 2 c.c. of rodinal (see Rodinal) ; but other developing agents of the aromatic series may be substituted for rodinal. (See below for formula with metol.) The develop-ment of the plate is slow, sometimes taking as long as twelve hours. When the development is complete, all that is required is to wash the negative; but if the whitish tone is objected to, the negative may be blackened by the mercuric chloride process