VARNISHING NEGATIVES, ETC.
The object of varnishing is to protect the gela tine film from scratches, damp, etc., and to pre vent silver staining due to the absorption of damp by both papers and negatives.
Hot Process.—The negative is warmed to drive out all moisture, and then allowed to cool. The negative need not be hot when the varnish is applied ; it is much more important that the negative is dry. Hot negatives may crack when cold varnish touches them, and the varnish may dry with marks and streaks, while a damp film will cause the varnish to dry milky, fish-scale markings possibly appearing later. The negative is held film side upwards in the left hand, the bottle of varnish in the right, and a pool poured into the centre of the plate and allowed to spread almost to the edges ; then the negative is tilted slightly until the varnish flows to the top right-hand corner, next to the left, then to the bottom left-hand corner, and finally to the bottom right-hand corner, from which corner the superfluous varnish is poured back into the bottle, holding the corner of the negative in the mouth of the bottle, and " see-sawing " the nega tive to prevent streaks. The negative is next
heated before a fire or over a gas-burner until the coating is hard and dry, it being kept on the move to obviate the formation of streaks.
Cold Process.—In applying cold varnishes the chief consideration is absolute dryness. The varnish is applied in the manner described for the hot process, although with care it may be brushed on sparingly with a soft brush. The negatives are set aside to dry in d. place where dust cannot form on them. Films may be im mersed bodily in some varnishes.
Varnish Substitutes.—Various substitutes for varnishing are known. One method is to place a very thin celluloid film between the negative and the printing paper, but this is a protection only during printing. Another method is to harden the film with tannic acid and alum.