British Kinematography (1948)

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BRITISH **SS K1NEMAT0GRAPHY The Journal of the British Hinematograph Society VOLUME TWELVE, No. 2. FEBRUARY, 1948 CONTROLLING THE ELON-HYDROQUINONE DEVELOPER G. I. P. Levenson, Ph.D., B.Sc* Read to the British Kinematograph Society on October 8, 1947. THE would-be controller of the Blon-hydroquinone developer hopes todo three things. He wants to achieve a correct sensitometric performance so that his developer gives the correct gamma, emulsion speed and fog in a convenient time ; to maintain this performance with the minimum of deviation ; and to do these things with the greatest possible economy in time and materials. As developers go, the Elon-hydroquinone solution is comparatively manageable, but it is still sufficiently unpredictable to cause much worry on the part of the controller. 1. SENSITOMETRIC AND ANALYTICAL CONTROL It is easy for the controller to tell what the current performance of his bath is, simply by processing a sensitometric strip. This photographic method of current assessment cannot be improved upon by chemical means. However, this photographic assessment is only an uncertain method of predicting what the bath will be doing tomorrow or in a few hours' time. A straight line on the sensitometric control chart tells the controller only that he has been successful up to date and gives no hint of a possible collapse of the bath in the near future. Chemical Changes In Bath This is especially the case in the first week or so after installing a new bath. For example, if a new D76 bath is installed in a system where it is circulated and exposed to air, it can be used extensively without replenishment and will appear to become more and more active and may even necessitate a i reduction in development time. Then suddenly it will collapse. The cause of this phenomenon becomes obvious when one follows the chemical changes in the composition of the bath. A negative bath is not severely exhausted by the normal negatives that are developed, and the acid liberated in the reduction of silver halides is not sufficient to counter the tendency for the alkalinity to increase as hydroquinone is oxidised atmospherically in the presence of sulphite. Since the buffering of the D76 type ♦Research Laboratories, Kodak Ltd.