A comparison of several developers and the specification of relative sensitivity

In a study of several photographic developers, including the international sensitometric standard, p-aminophenol, it was found that the latter agent is not as satisfactory as certain metol-hydroquinone developers in two respects: (1) The "toe" region of the characteristic curve is increased, accompanied by an increased inertia; and (2) the recommended formula is not well chosen in that the solution is supersaturated. It is also found that the presence of soluble bromide in some developers gives, with some emulsions at least, an increased sensitivity with prolonged development. This effect should prove useful in those cases where high contrast is not detrimental. It was observed that, in general, the ratio of values of the two sensitivity indices varied considerably with development time. In fact, under certain conditions, values of one index {IIi) may be decreasing while values of the other 0-1Em) are increasing with development time. In order to consider these apparently contradictory changes a definition for relative sensitivity has been set up. From this definition it follows that comparisons of sensitivity may be made only when the emulsions have each received equivalent development. The type of emulsion with which each of these indices is particularly applicable is also indicated. The findings of Luther, that the gradient of the curve above the inertia point is approximately one half y, are confirmed. The application of this constant to coordinate the inertia and gradient methods of specifying sensitivity is discussed. This information should help clear up the confusion surrounding the measurement of the sensitivity of photographic emulsions. CONTENTS Page