Development and Developers
slight deposit of oxalate of lime (caused by the washing water) by pouring over or immersing it for half a minute in the following
After which it should be thoroughly washed to complete the process. When quite dry the opal can be finished in mono-chrome or water colours as may be desired, or may be varnished with crystal varnish.
Caution. It is of the greatest importance that not the slightest trace of hyposulphite of soda be allowed to contaminate the dishes or measures employed in developing or toning the opals. Therefore great care should be exercised and the hands well washed between the various operations.
The above instructions (mainly due to Mr. Edwards) comprise details of most matters connected with development. Various formulae for ferrous-oxalate developer are given in the article on Bromide Paper, and the following formula, recommended by Messrs. Mawson & Swan, is excellent for dry plates: -
Ferrous sulphate ... ... ... ... 1600 grs.
Citric acid ... ... ... ... ... - 120 ,,
Distilled water to make ... ... ... 10 fluid ozs.
Distilled water should be used, otherwise the lime in ordinary water will cause turbidity from formation of oxalate. A will keep indefinitely, but B should not be used after it turns brown or yellow. When required for use, pour four parts of A rapidly into one part of B. The resulting solution will be of a deep red colour. After development and fixing, the plate frequently ex-hibits an opalescent appearance ; this is a deposit of oxalate of lime that forms in washing: to remove it, immerse the plate, after thorough washing in