Electricities of Stripping and of Cleavage

Abstract

IN the ordinary process of giving a glazed surface to photographic paper prints by leaving them to dry face downwards upon clean glass, enough electricity is, I find, developed at the moment of separation between the dry glazed print and its glass support to produce a pretty bright illumination in the dark. “Solio” and other gelatino-chloride printing papers being very liable to adhere obstinately to a glass plate in this process, I have only constantly employed it with albumenised printing paper, and have then often noticed strong electrical attraction between the glass plate and the freshly separated paper. Not all glass plates, but apparently only very hard unhygroscopic ones, with a low percentage of soda in their composition, serve the purpose well; and even on these the print must not be freed from superfluous water by any pressure, but by swinging the plate until the water is sufficiently expelled to leave the glass and paper adhering firmly to each other. The paper can be then further freed from water by wiping it on the back, very lightly, with a soft cloth, and any intrusive air-bubbles seen through the glass can be driven out by stroking the back of the print very lightly with the finger. Left then to dry quite horizontally with the paper upwards, the latter will in hot, dry weather or in a very dry, warm room separate itself at last more or less completely from the glass; but in ordinarily damp atmosphere, and cold weather, remains, though sensibly quite dry, adhering to it. The slightest warmth of sunshine or of a fire or gas flame applied to the plate is then enough to make the paper crisp, and leave the glass. This it does with audible clicks as the adhesion breaks up here and there, showing that a state of pretty strong tension prevails in the thoroughly dry paper and the coat of albumen until these can break loose from their support.