SULPHIDE TONING Bromides.—Success depends on the use of a fresh developer for each print, full development, drying after fixing and before toning, and thorough bleaching to a light colour.
Two stock solutions should be prepared, each of which will keep indefinitely.
After bleaching thoroughly, the print must be washed ; in addition, an acid bath must be used whenever the working solution contains solution B. The acid bath is hydrochloric acid 3o mins., water about 6 oz. ; its object is to prevent the combination of the mercury with the gelatine. The print should be taken from the bleaching solution, washed in about three changes of water, and then immersed in the acid solution for two or three minutes. A second and third acid bath should be used, and then the print washed again for about twenty minutes in several changes of water. When the toner for pure black is used for bleaching, the print is intensified considerably, and allowance must be made in printing. There is also a slight strengthening when using the solutions for deep brown and brown-black.
When sufficiently washed after bleaching, the prints should be treated with the sulphide solution. Prepare a stock solution of 520 grs. of
sodium sulphide in io oz. of boiling water, stor ing it in a screw-stoppered bottle. The working solution is 4o mins. of the stock solution in sufficient water to make i oz. This should be used once, and then thrown away.
Pine red and red-brown tones can be obtained by substituting a stock solution of i oz. of sodium sulphantimoniate (Schlippe's salt) and + oz. of sodium carbonate in sufficient water to make 9 oz.
The prints are bleached in : Bleaching solution A . . s part Water . . . . . is parts Wash for half an hour, and immerse in one of the following mixtures :— The prints should be washed thoroughly for about half an hour, and then dried. Bleaching solution B—the mercuric solution—must not be used with sodium sulphantimoniate.
attempts have been made to introduce a method of toning P.O.P. by the sulphide process, but they have not been suffi ciently successful to render the process suitable for ordinary working.