New Method for the Dry Hypersensitization of Photographic Emulsions

Abstract

Hypersensitization by mercury vapor increases the speed of photographic negative emulsions about 50 to 150 per cent, depending upon the emulsions used for the treatment. The important features of this method that make it superior to the well known wet-hypersensitizing methods are: (1) The film does not have to be put through a bathing process and then dried. (2) The mercury vapors are active also upon tightly wound spools of film, the sensitizing effect being uniformly spread over the whole length (e. g., of a 1000-foot roll of 35-mm. motion picture film). If sufficient time is available for hypersensitizing, the films need not even be removed from their original wrappers, as the mercury vapors diffuse sufficiently through the wrapping material. (3) The increase of sensitivity is general throughout the range of wavelength of light to which the film was originally sensitive. (4) Not only can unexposed film be hypersensitized by this method, but it is also possible to intensify the latent image with mercury vapors.(5) The stability of the film is not permanently affected, although the increase in speed is gradually lost over a period of four weeks of aging. The clearness, however, remains the same, and may even improve somewhat. By a second treatment with mercury vapor the hypersensitization can be renewed in a film that has recovered from previous hypersensitizing.