When a large number of plates have been exposed and the first developed indicates that all have been overtimed, then a 50 per cent. solution of citrate of soda, used with judgment, might result in saving the lot.
When over-timing makes itself visible unexpectedly and it is feared that the development will have proceeded too far before the retarder can act, a good plan is to take the plate out of the dish and flow over it a solution of citric acid, containing a little chrome alum, [p061] which will immediately stop the action of the developer and give time to make other arrangements.
Water 60 oz. Bromide of ammonium 60 grs. Strong liquor ammonia 2 drs.
No. 1 or pyro solution 1 dr. No. 2 or ammonia solution 10 oz.
This will be enough to develop three or four 8×10 plates, if they are properly timed.
The above is one of the best forms of ammonia pyro developer; it gives negatives of very fine quality.
Many dry plates, on development with ammonia and pyro, show a green fog by reflected light, and a pink or red fog by transmitted light; this fog does not materially injure the printing quality of the plate, but spoils its appearance to the eye, and for that reason many establishments have given up the use of ammonia and in its place use soda or potash.
From the difficulty of judging when the development has reached the right point, in consequence of the opacity of the gelatine film, many negatives are finished before they have acquired sufficient density in development. As a result of this, much attention has been given to the discovery and preparation of redeveloping or intensifying solutions, many formulæ [p062] for which have been published; among the best are the following:
Bichloride of Mercury 120 grains. Dissolved in hot water 16 oz.
Add to this a strong solution of Iodide of Potassium drop by drop, until the red precipitate begins to redissolve, then add a few grains of hyposulphite of Soda, or enough to clear the liquid.
When required for use pour part of this solution into a tray of a suitable size for the plate, add an equal amount of water, then immerse the plate and keep the solution in motion. You will immediately notice a change in the color of the film; take the plate out, and if it has gained enough strength, wash it and set it up to dry; if not, give it more.