PLATINGT VEE Zi 
potassium bichromate; but, in this case, printing must be 
carried further than usual. In place of the bichromate, 0.5 
to 1 per cent of ammonium persulphate may be used, which 
shortens the scale of gradation, and this is particularly useful 
in the case of over-printing or when thin flat negatives are 
used. 
SeprA Paper, CoLtp BatH.—Brown or sepia tones are 
readily obtained by the addition of a mercury salt to the 
sensitiser, and the best is mercuric citrate, prepared as fol- 
lows: 
Yellow mercuric oxide 5g 96 gr. 
Citric acid 255 480 gr. 
Water 100 ccm 4 oz. 
Heat until dissolved, and filter. The actual sensitiser 1s: 
Ferric oxalate sol. 8 ccm 130 min. 
Potassium chloroplatinite sol. 4 ccm 65 min. 
Mercuric citrate sol. 1to4ccm 16 to 65 min. 
Sodium chloroplatinate 
sol. 2to5drops 2to5 drops 
This should be applied as described above and to the same 
area of paper. The best developer is one of the following: 
Neutral potassium 
oxalate 100 to 300g 154 to 462 gr. 
Water 1000 ccm 16 oz. 
Or: 
Potassium oxalate 70 to 300g 538 to 2304 gr. 
Potassium phosphate 30 g 230 er. 
Oxalic acid 10g 77 gr. 
Water 1000 ccm 16 oz. 
The stronger the developer, the more rapid its action and the 
softer the print; the more mercury salt used, the weaker 
should be the developer; with contrasty negatives and with 
less mercury, the stronger should be the developer. Prints 
