292 PHOTOGRAPHIC FACTS AND FORMULAS 
chloric acid until there is a faint smell of chlorine. Or mix 
1 part of chloride of lime with 1 part of sodium carbonate 
and 10 parts water, stir well, filter or decant the clear solu- 
tion, add 90 parts water, and faintly acidulate as above. Im- 
merse the stained print in either of these solutions until 
bleached; then wash and dry. This treatment cannot affect 
the image. 
VARNISHING PLATINUM PRINTS.—Frequently platino- 
types appear rather dull and sunken-in compared to their 
appearance when wet. Application of print varnishes will 
then brighten them up; but the surface should not appear 
glossy. Artist’s size, diluted with warm water, may be used; 
or megilp may be used in the same way; or the print may be 
sprayed or lightly painted with 1 part of mastic varnish 
diluted with 8 parts alcohol. For stronger effects ordinary 
negative varnish may be applied locally or generally with a 
brush. Or a solution of gelatine, about 4 per cent, may be 
made, the print bodily immersed in this while warm, and 
hung up to dry. Or the print may be rubbed with en- 
caustic paste. 
PLATINUM ReEsipuES.—The high cost of platinum makes 
it well worth while to save all platinum residues. Scraps of 
paper, if unexposed, should be exposed to daylight and 
developed in the usual way. Print trimmings should be 
burnt, the scraps of the paper previously dealt with being 
mixed with them. The developer should be mixed with one- 
fourth its volume of saturated solution of ferrous sulphate, 
boiled, and the platinum precipitate allowed to settle or be 
filtered out. The first and second acid baths should also be 
saved, boiled down until of convenient bulk, at least one- 
fourth their original volume, and scrap zinc added. Black 
platinum is precipitated, and may be collected on a filter. 
It is not worth while to make the residues into platinum salts, 
en ma 5 _—" 
