Richard Smith


The development characteristics of mercaptoacetic acid monobaths were compared with those of sodium thiosulfate monobaths at varying fixing-agent concentrations. The following differences were noted: (1) it required four times more moles-per-liter of sodium thiosulfate than metcaptoacetic acid to obtain the same rate of fixation; (2) the mercaptoacetic acid monobath produced less silver than the sodium thiosulfate; (3) KODAK Panatomic-X Film developed in a mercaptoacetic acid monobath had a covering power greater than or equal to that produced by development in the same phenidone-hydroquinone developer without any fixing agent, whereas the covering power of the sodium thiosulfate monobath was less; (4) the density growth of a mercaptoacetic acid monobath showed an initial sharp rise followed by a period of zero growth, whereas the sodium thiosulfate monobath showed a much longer and slower period of density growth; and (5) the time required for a mercaptoacetic acid monobath to reach its maximum density was independent of fixing-agent concentration, whereas that of a sodium thiosulfate monobath increased with decreasing fixing-agent concentration. It was concluded from the comparisons of the development characteristics of the two monobaths that the development of the mercaptoacetic acid monobath proceeded primarily by chemical development, and the development stopped before all of the exposed silver halide could be either removed from the emulsion by the mercaptoacetic acid or reduced to developed silver by the developer. The development of the sodium thiosulfate monobath proceeded initially by chemical development, but after a certain period of time, a significant amount of solution physical development occurred.

Library of Congress Subject Headings

Photography--Developing and developers; Photography--Processing

Publication Date


Document Type


Department, Program, or Center

School of Photographic Arts and Sciences (CIAS)


Carroll, B.


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