SULPHIDE TONING Zao 
Iodine 10¢ 77 gr. 
Water 1000 ccm 16 oz. 
In these last two baths the paper turns a deep blue, which 
may be discharged by immersion in a 2 per cent solution of 
potassium metabisulphite or sodium sulphite acidulated with 
a little sulphuric acid. 
The following was recommended (Greenall) for commer- 
cial work, as it saves the cost of the halides: 
Potassium ferricyanide 23 ¢g 177 st: 
Sodium phosphate PSs 883 gr. 
Water 1000 ccm 16 oz. 
Bichromate baths have been recommended, but they require 
much longer washing to remove the yellow bichromate stain 
than the other baths. Sedlaczek’s formula is: 
Potassium bichromate, 
sat. sol. 100 ccm oz. 
Hydrochloric acid, 10% sol. 100 ccm faz: 
Potassium bromide 100 g 1 oz. 
Water 1000 ccm 10 oz. 
Blake-Smith recommended : 
Potassium bichromate 2s: 160 gr. 
Sulphuric acid 40 ccm 307 min. 
Salt 100 g 768 gr. 
Water 1000 ccm 16 oz. 
Too long washing of the bleached prints causes yellow tones; 
about 10 minutes in running water is enough. The toning 
solution is sodium sulphide, and the best results are obtained 
with the hydrated salt (pure analytical agent). Ordinary 
technical sulphide should be made into a stock solution and 
boiled for a short time until a black precipitate forms, or 
allowed to stand for several days, and then filtered. Old 
deliquesced salt should not be used, as it consists in great part 
of hypo and caustic soda, which reduce the strength of the 
