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Stripping Varnishing

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VARNISHING, STRIPPING, NUMBERING, CLASSIFICATION, AND STORAGE OF NEGATIVES 477. Varnishing of Negatives. The varnishing of negatives ensures them against numerous accidents. It is advisable for negatives which are required for large numbers of prints, and which in time become scratched by rubbing. Varnishing is also advisable for negatives from which a large number of prints are required on silver print-out papers. In this way, any risk of staining the negative by soluble silver salts from the paper is avoided when the printing is done in very damp weather. Varnishing is strongly recommended for negatives which have been retouched to any extent, but it is essential, in this case, to make sure, by trial on a waste negative, that the varnish which it is proposed to use will not destroy the pencil retouching by dissolving the film of medium which serves as a substratum. Finally, when enlarging by direct light, varnishing of the negative lessens the effect of minor superficial scratches which are not noticeable in contact prints. Certain varnishes, called hot negative varnishes, can be used only if the negative has been previously warmed to a temperature of at least 90° F. Unless this is done, a matt surface is formed by condensation of the moisture in the atmosphere on the surface of the varnish, which -s cooled by the evaporation of the solvents.

Warming of the negatives is dispensed with if cold negative varnishes are used, the only precaution necessary being thorough drying of the negative beforehand. Varnishing of nega tives, however, should never be carried out in a damp or cold room.

478. Preparation of Varnishes. Varnishes pre pared with alcohol are generally used for glass negatives, and, since they do not dissolve the dammar of the medium, can also be applied to retouched negatives. Ordinary collodion to which a very small quantity of castor oil has been added is occasionally used ; and a solution of celluloid in amyl acetate is sometimes em ployed. Alcohol varnishes should never be applied to films (which seldom require varnish ing), as the alcohol dissolves the camphor, which is one of the essential constituents of celluloid. Instead, a water varnish for retouched negatives, or a benzene varnish in the case of unretouched ones, should be used.

It should be borne in mind that the various solvents usually employed in the preparation of varnishes are inflammable ; if it is desired, therefore, to hasten solution of the resins by warming the mixture, the operation should be carried out on a water bath after the flame has been extinguished. Ether, or any mixture con taining ether, should never be heated. All risk. of fire can be avoided by the use of non-inflam mable solvents, such as carbon tetrachloride and other chloro compounds, in the preparation of varnishes.

Hot Negative Varnish. The following varnish. will take retouching quite easily, and is com pounded in the cold or by aid of a moderately warm water bath.

Sandarac . . . 3 oz. (rso grin.) Essence of lavender' . 145 min. (15 c.c.) Alcohol, 96%, to make . 20 OZ. (1,000 C.C.) Cold Negative Varnishes. Waste pieces of cel luloid film can be used in the preparation of the following varnish, after they have been lexiviated and dried— Celluloid . . 150-2oo gr. (15 to 20 grin.) Amyl acetate, to make . 20 OZ. (I,000 C.C.) For unretouched negatives, one of the follow ing varnishes, which take work with a pencil easily, can be used— Sandarac . . 2 oz. (100 grin.) Acetone . . 8 oz. (400 grin.) Crystallizable benzene . 8 oz. (40 grin.) Denatured alcohol, to make 20 oz. (1,000 c.c.) or— Powdered copal resin . oz. (so grin.) Gum dammar . . . 175 gr. (2.o grin.) Carbon tetrachloride, to make 20 oz. (1,000 C.C.) The latter must be prepared boiling and filtered while hot.

Water Varnish for Films. 21- oz. (125 gun.) of white gum lac are dissolved in 5 oz. (250 c.c.) of alcohol. When dissolved, 4 oz. (200 c.c.) of concentrated ammonia are added. The gum lac is thus precipitated in a finely-divided state, and the whole should be shaken several times to re-dissolve it (to a soapy resinous state). Boiling water is added to bring it to a volume of 20 oz. (r,000 c.c.), and the whole is kept on a water bath for a while. The liquid is never quite clear -I I- -1 1 C4- 1. 1, • 411U Slit, URI 'ASCU. al Lel 11c1, stood for some time.

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