154 PHOTOGRAPHIC FACTS AND FORMULAS 
dissolve, the solution sinks to the bottom of the bottle, and 
fresh solvent takes its place. This also frequently obviates 
the necessity of filtering. Another plan is to mix the resins 
with coarse glass grains or beads, about half the size of a 
grain of wheat. 
DEVARNISHING NEGATIVES.—Sometimes it becomes neces- 
sary to remove the varnish from negatives and this usually 
can be accomplished by soaking in strong alcohol, and then 
using gentle friction with a pad of absorbent cotton. It is 
preferable to use only just enough alcohol to cover the surface 
of the negative, and to apply two or three successive alcohol 
baths. A more energetic solvent is a 2 per cent solution of 
caustic potash, or soda, or ammonia in alcohol, which may be 
used for the first bath, and then followed by clean alcohol. 
PRINT VARNISH.—Sometimes used for brightening up 
matt surface papers: 
Gum sandarac 110¢g 134 oz. 
Benzol 400 ccm 6% oz. 
Acetone 400 ccm 64 oz. 
Alcohol, 90% 200 ccm 3 oz. 
Or 
Gum dammar 60 g 1 oz. 
Ether 500 ccm 8 oz. 
Benzol 500 ccm 8 oz. 
These may either be applied with a brush locally to the 
shadows or the prints floated face downwards on the varnish. 
BLack VARNISH.— 
Shellac 200 g 3 1/50, 
Denatured alcohol 1000 ccm 16 oz. 
Aniline black, spirit soluble I5¢ 115 gr. 
ALCOHOLIC CoLD VARNISHES (V alenta).— 
Gum sandarac 180 g 1382 gr. 
Alcohol, 96% ~ 1000 ccm 16 oz. 
