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in photography, the process of increasing the optical density of a photographic image, primarily for the correction of underexposed or underdeveloped negatives. Intensification is the opposite of reduction. It may be accomplished by the accumulation of a metal, such as mercury or silver, or of some opaque compound on the silver grains in an image, as well as by toning. Because of the attendant complexity, there is no practical intensification process for multilayer color materials.
In intensification, the metallic silver in an image is bleached with solutions of mercuric chloride, potassium bichromate, or other compound, and subsequently darkened in highly active developers, ammonia solutions, or other agents. Intensification results from reduction of the bleaching agents to finely dispersed metal powders (mercury from mercuric chloride) or difficultly soluble opaque compounds (Cr2O3 · CrO3 from potassium bichromate), which are precipitated on the metallic silver grains of the image to create increased optical density. On bleaching with copper bromide, darkening is effected by a silver nitrate solution as a source of additional metal, which is precipitated on the image. If intensification is achieved by toning, the negative usually turns brown. Furthermore, its effective photographic opacity increases as the emulsion absorbs blue light, to which positive photographic materials are most sensitive.
Intensification may be classified as proportional, subproportional, or superproportional. In proportional intensification the optical densities increase in proportion to their initial values, but very low densities show almost no increase. In subproportional intensification, low densities increase substantially more than average and high densities. In superproportional intensification, high densities increase more than small and average densities.
REFERENCESTsyganov, M. N. Ustranenie defektov fotograficheskogo izobrazheniia. Moscow, 1957.
Mikulin, V. P. Fotograficheskii retsepturnyi spravochnik, 4th ed. Moscow, 1972.
L. D. PERVOVA