A Developing Machine for Sensitometric Work

Sensitometric testing of photographic materials requires that the laboratory be able to obtain the same results, with a high degree of precision, for identical samples of material, although the individual tests may necessarily be made at widely different times. All factors tending to influence the results must be held constant over long periods of time. — A developing machine is described designed for a laboratory in which a relatively large volume of sensitometric work must be done. It accommodates sixty strips positioned vertically on six metal racks, which can be lowered into the developer simultaneously and removed either simultaneously or individually, so that different development times may be given to different parts of the load. — The developer circulation across the face of the exposed material is sufficiently rapid that further increase of agitation produces little if any increase in the rate of conversion of latent image into metallic silver. The circulation is of two sorts: (1) a relatively slow, uniform movement of developer in the vertical direction produced by a propeller that forces the developer down into a well external to the main tank, from the lower end of which it spreads out beneath a perforated false bottom in the tank and rises throughout the body of the tank, flowing back again into the top of the well; (2)a much more violent agitation produced by vertical paddles moving back and forth close to the exposed surfaces. Both agitating elements are driven by a synchronous motor, assuring the same rate of circulation at all times. The entire machine is jacketed by thermostatically controlled water at 65° ± 0.1°F. — Results show that the circulation throughout the body of the tank is so nearly uniform that they are not influenced by (a) whether the heavily exposed end of the sensitometric strip is up or down, (b) the position of the strip within the tank, or (c) whether a complete or partial load of strips is developed at one time. Results indicate also that the agitation is sufficiently violent that the rate of conversion of latent image into metallic silver is at or near the maximum attainable. Uniformity and reproducibility of development is very markedly superior to that attainable with any type of hand- or machine-rocked tray with which the authors have had experience, and the use of the machine marks a very definite advance in the precision with which sensitometric values may be established.

Print ISSN

0097-5834

Published

1937-01

Content type

Original Research

DOI

10.5594/J08594