A latent image may be produced in a photographic emulsion by applying mechanical pressure to the emulsion. The mechanism of this latent image formation has been obscure. An investigation of the effect has been carried out with Ilford Nuclear Research Emulsions which were observed to be especially sensitive to pressure.
The experiments described below were of two kinds: (1) Photographic plates were placed between smooth steel surfaces in an hydraulic press and pressures in the range 70 to 7000-kg cm−2 applied. (2) A scriber was drawn across the surfaces of emulsions under varying conditions of pressure, speed, etc. The results of these experiments suggested that the pressure effect might be explained as a temperature effect, the temperature resulting from heat generated by friction.
Such estimates as could be made of the temperature to be expected in individual silver bromide grains at the surface of the emulsion under the conditions of experiment indicated temperatures of the order of 100 to 1000°C. This is in general agreement with such other estimates and measurements of surface temperatures involved in solid friction that have been attempted.
The effect of temperature on a silver bromide grain has been considered in terms of the Gurney and Mott theory of the latent image. While gross uncertainties exist in the values of the activation energies involved in such a calculation, it at least seems plausible that temperatures of the order of magnitude expected could produce a permanent latent image.
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