Studies on the Photographic Fixing Process with Thiocyanate Salts (I)

Fixation of thiocyanate salts

Abstract

Thiocyanate salts are useful as a rapid fixing agent on silver halide emulsion. These salts, however, show the soluble effect on developed silver particles and softening of gelatin emulsion layer, and also form the insoluble complex salts in the emulsion layer while washing.
The studies to make good these defect were carried on the preparation of rapid fixing solution with thiocyanate salts.
On this paper, the photographic properties of the salts as a fixing solution were investigated under the various conditions. Both the clearing time of the emulsions and the effects on the dissolution of developed silver particles were examined, varying the component of the salts in the solution, by measuring the optical density decrease.
The results obtained are as follows:
1) The clearing time of thiocyanate salts such as ammonium, sodium and potassium are shorter than that of thiosulfate, and the results depend on the order of Ca⁺⁺, Mg⁺⁺, Li⁺, Na⁺, K⁺, NH₄⁺ among these salts.
The optimum concentration of thiocyanate was found in the range of 15-20%.
2) 0.2 mol/l or more concentraton of thiosulfate should be added in 15% ammonium thiocyanate solution to prevent the formation of insoluble salts in washing process.
3) The effect of thiocyanate salts on the dissolution of developed silver particles is negligible in the range of normal fixing time.