66 THE WOMBAT. 



TONING AND FIXING. 



By J. H. Harvey. 



(Abstract of a paper read before the Gordon College Amateur 

 Photographic Association, 13/5/98.) 



( Continued from p. 13. ) 



The reason is probably that a minute portion of gelatine is 

 taken up by the bath from the paper during the toning 

 operation, and that when the solution is put on one side after 

 toning a batch of prints, this organic impurity sets up 

 decomposition and the gold is thrown down. But the making 

 up of a large quantity of bath at one time is no great task, 

 and if a gallon is made at once there will be sufficient to tone 

 about eight sheets of paper ; the used bath can then be thrown 

 away as there is very little gold left in it, and when the next 

 toning of prints takes place fresh solution is used from the 

 bottle, and the operation proceeds steadily. If made up with 

 good water and kept in the dark, the bath will remain in 

 order for a considerable time, provided that no solution that has 

 been already used is added to it, and the advantage of using 

 a pure uncontaminated bath for each batch of prints must be 

 self-evident. (Before leaving the subject of the composition of 

 toning baths it may not be out of place to refer to a method 

 of preparing the sulphocyanide toning bath recommended by 

 Belitzski. He says that it yields very rich tones from brown 

 to blue, but never double toning. To make the bath, take 1 

 grain of dry brown chloride of gold and dissolve it in 90 c.c. 

 of distilled water ; in a porcelain dish dissolve also 2 grams 

 of pure ammonium sulphocyanide in go c.c. of distilled water; 

 add the gold to the sulphocyanide and stir quickly, heat the 

 mixture over a spirit-lamp, stir. At a temperature of 50°c. 

 the solution becomes a bright transparent red, and at 75 it 

 becomes colourless ; then heat until it boils. Allow to cool, 

 filter, and wash the filter until the filtrate measures 200 c.c. 

 When cool it becomes yellow again, probably through the 

 formation of some auric sulphocyanide, but this is immaterial. 

 This solution will keeD for several weeks, and it is as well to 

 keep it in the dark. If potassio-chloride or sodio-chloride of 

 gold is used, take, according to the actual proportion of gold 

 present, from 15 to 2 grams of the salt. For use, the solution 

 should be diluted with from twelve to fifteen times the quantity 

 of water.) 



The above is copied from Belitzski's article on the subject 

 which was reproduced in the British Journal of Photography 

 last January, and the reading of which will be found highly 

 interesting by those who have any love for the chemistry of 

 the subject. 



