Sensitivity, Fog and Grain Size in Single Emulsions: A New Experimental Approach

Abstract

It is shown that fully developed grains in well-hardened layers of emulsion are of similar size and shape to undeveloped grains. This effect can be used to determine directly the response of grains of different size classes to exposure plus development, and development alone, in dilute layers of emulsions of medium to large grain size.

This approach has been used to study the grain size-sensitivity and grain size-fog relations in an emulsion of thin tabular grains having a mean area of 5.9 pm2, and sensitized to three distinct levels with sulphur plus gold, namely, under-, optimally-, and over-sensitized. Major findings were as follows:

(a) At optimal and over-sensitization the photon sensitivity is substantially invariant over small to medium grain sizes, but falls at large grain sizes. Thus the latter effect is specific to grain size and is not a property of an emulsion as a whole.

(b) The fog fraction increases with increasing grain size, and increases by the same factor at all sizes with increasing sensitization. The latter effect implies that the rate of the sensitization process itself is invariant with size.

(c) In terms of sensitivity growth the sensitization at small grain sizes proceeds more slowly than at large sizes. Taken in conjunction with (b) this indicates that grain properties which inhibit surface-image formation are more ef-fective in small than in large grains.

(d) Grain sensitivity in terms of developed frac-tion, and corrected for fog, is substantially independent of fog fraction. This means that fog growth does not selectively remove the most sensitive grains.