Analysis of the particle-size distribution of the grains producing a photographic image

Abstract

1. 1. The concentration of silver halide grains (number per square centimeter) in the multilayer photographic film coating and their size distribution were determined for the emulsion under investigation. These two analyses were also made for the halide grains unaffected by exposure and development for the steps of an unfixed sensitometric step wedge; a corresponding normally fixed density step wedge was used to determine the densities. The concentration and size distribution of the developable grains that, upon exposure and development, produce the densities of the step wedge were obtained by subtraction of the data of the residual grains from the corresponding data of the original total number of emulsion grains. 2. 2. The grains of this emulsion were formed during precipitation principally on two types of nuclei, as evidenced by the break in the normal function. 3. 3. The ratio of the number of grains, N d, to the optical density, D, is a constant, N d =4.0×10 8·D , which is substantially unchanged between 3- and 12-min. development. 4. 4. The relation between the average size (as projective area) of the developable grains and the density is practically a linear one. 5. 5. The size distribution of the undeveloped grains in the maximum densities, D max, by exposure, with increasing development times, is shown graphically and discussed. About 32 per cent of the grains are still undeveloped as the development approaches maximum development. The size distribution resembles that of a simple negative exponential form, with the smallest grains being predominant in number. These fine grains have a very low sensitivity. 6. 6. A case is cited in which a very slow but definite increase of density occurred upon prolonged exposure after the usual shoulder was reached. 7. 7. Since the size distribution of the residual undeveloped grains of each exposure step resembles that of the undeveloped emulsion in type, the effect of exposure on the statistical size-distribution parameters is presented. For a lognormal distribution, the ratio of the arithmetic average to the median size, x ̄ a / x ̄ med , or the difference of their logarithms, is simply related to the fundamental dispersion, K, of the emulsion precipitate and is a good measure of it. 8. 8. The arithmetic average size and also the median size of the developable grains decrease linearly with increase of the logarithm of the exposure for the range studied. The fundamental dispersion of the developable grains, however, increases with exposure.