14 PHOTOGRAPHIC FACTS AND FORMULAS 
about 90 seconds and will be complete in about 2 minutes. 
During the silvering, the bath should be gently rocked: to 
prevent striz. As soon as the liquid begins to become cloudy 
or show spicules of silver, it should be poured off and a 
second quantity of solution applied. Several coatings may 
be thus applied until the desired thickness is obtained. At 
the close of the operation the surface has a slightly reddish- — 
brown appearance. It should be washed with successive lots 
of distilled water and dried, standing it on white blotting 
paper. When the film is perfectly dry, it can be polished 
with a soft chamois, enclosing a pad of absorbent cotton and 
rouge; the rouge used for gold is the best. The alcohol is 
used to prevent the formation of a precipitate in the solution, 
and, if this forms, too much formaldehyde has been used. 
If too little formaldehyde be used, the film has a pronounced 
reddish-brown colour and is punctuated with numerous pin- 
holes. In all cases, the formaldehyde must only be added 
just before applying the mixture to the glass. If too high a 
temperature be used, the deposit forms too rapidly and be- 
comes powdery. For small mirrors, the glass may be placed 
in a dish of porcelain or glass, and the alcohol bath may be 
omitted. If, instead of using the silvered surface as the 
mirror, the glass side is used, then the silver coat should be 
covered with: 
Gum dammar 10¢ 77 gr. 
Bitumen of Judea (asphalt) 100g 770 gr. 
Red ochre 200 g 3, 1/3 on: 
Benzole 1000 ccm 16 oz. 
The ammoniacal solutions of silver are dangerous to keep in 
stock, as they may form fulminating silver which is explosive. 
LINE DRAWINGS FROM Prints.—Waterproof drawing ink 
should be used in drawing over any desired part of the print; 
then immerse it in: 
