SULPHIDE TONING 237 
Potassium ferricyanide, 
20% sol. 200 ccm 4 oz. 
The mixture turns milky, but clears up on stirring well. 
Then add: 
Potassium bromide, 10% sol. 200 ccm 4 oz. 
Glacial acetic acid 50 ccm Y oz. 
Stir until the precipitate dissolves. The prints should be 
well washed, and, in from 10 to 15 minutes after immersion 
in the bath, assume a very pleasing brown tone. 
Sulphide-ferricyanide (Blake-Smith)—Three stock solu- 
tions are required: 
A. Sodium sulphide, pure 100 g 4 oz. 
Water 400 ccm 16 oz. 
B. Sulphuric acid, pure 25 ccm lioz: 
Water 250 ccm 10 oz. 
C. Potassium ferricyanide 50 g 1 oz. 
Water 500 ccm 10 oz. 
For use mix: | 
A solution 60 ccm 460 min. 
Water 1000 ccm 16 oz. 
Then add: 
B solution 180/cem a) Zioz’ Gdn: 
And, finally, add: 
C solution 500 ccm 8 02. 
Toning should be complete in from 2 to 5 minutes. 
Ammonum sulphide-ferricyanide — 
A. Potassium bromide llg 85 er. 
Potassium ferricyanide Si 269 gr. 
Water 1000 ccm 16 oz. 
To this, add: 
B. Ammonium sulphide 25 ccm 192 min. 
Water 100 ccm 1Y4 oz. 
This last solution should be mixed just before use. 
