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A QUICK TEST FOR DETERMINING THE DEGREE OF EXHAUSTION OF DEVELOPERS*
MERLE L. DUNDON, G. H. BROWN, AND J. G. CAPSTAFF INTRODUCTION
The fine grain borax developer formula,1 originated by J. G. Capstaff and R. A. Purdy, was presented to the trade in the Eastman Duplicating Film booklet issued in January, 1927,2 and has since been widely adopted.
The end of the useful life of the borax developer is reached when its degree of exhaustion is such that it causes an apparent loss of exposure on the film, although the desired contrast can still be obtained by longer development.3 With ordinary developers, this condition does not become serious, and they can be used until the required time of development becomes too long. The loss of available image peculiar to exhausted borax developer cannot be detected by examining a developed film of unknown exposure, but if two pieces of film having identical exposures are developed to the same gamma in fresh borax and in exhausted borax, the film developed in the latter will appear to have had less exposure. For this reason, it is obviously important that borax developer should not be exhausted too far when used for negative film.
In this communication, a quick test is described which gives a reliable indication of the degree of exhauslion of the developer, and the application of this test to borax developer is discussed in detail.
* Communication No. 405 from the Kodak Research Laboratories.
1 Elon 2.0 grams Sodium sulfite (anhydrous) 100 . 0 grams Hydroquinone 5.0 grams Borax 2.0 grams Water to 1.0 liter
2 Eastman Duplicating Film, Eastman Kodak Company, Rochester, N. Y. (1927).
3 CARLTON, H. C., AND CRABTREE, J. I.: "Some Properties of Fine-Grain Developers for Motion Picture Film," Trans. Soc. Mot. Pict. Eng., XIII (May, 1929), No. 38, p. 406.
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