File:The American annual of photography (1922) (14594911620).jpg

Identifier: americanannualof36newy (find matches)
Title: The American annual of photography
Year: 1922 (1920s)
Authors:
Subjects: Photography
Publisher: New York : Tennant and Ward
Contributing Library: Harold B. Lee Library
Digitizing Sponsor: Brigham Young University

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ade in the clothing of the personnel, and even the latterwere changed where they were directly connected with thecoating of the plates. But still the spots persisted. Dr. Lueppo-Cramer was responsible for their elimination,and as he said they gave him no rest in the day and no sleepat night. It was customary to pile the plates ready for coatingin lots of fifty and put them into a cardboard box. Aftercoating the upper plate always showed the spots, but not theother forty-nine. Examining the cover showed that a stripof black calico was glued to the inside and this was thencovered with white paper. The plates had gradually wornaway the paper in places leaving the cloth bare. Minute par-ticles of this cloth settled on the plate and caused these spots.And this coloring matter was then the first desensitizer. Thestrange behavior of the dye stuff led Dr. Lueppo-Cramer totry the action of solutions of a number of dyes on plates afterexposure and before and during development. He found that 94
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Q<O h-1CD w 95 the sensitiveness of the emulsion to light had been very muchreduced and a much brighter light could be used during de-velopment. Phenosafranine gave the best results. One part of thisred dye was dissolved in two hundred parts of ethyl alcoholand distilled water added to make solution i to 2000 (aboutfour grains per pint) and 5 c.c. added to 100 c.c. of developer(about two drams in five ounces). After placing the platein this mixture for one minute the development can be fin-ished in bright yellow light, or even by candle light at sixfeet. Even panchromatic plates can be so developed. Thedye being red it was thought that possibly it acted as a screen.Other dyes were tried including blue, and it was found thatalso some of the latter possessed this property although notso pronounced. Further investigation showed that the dyeshad a chemical action on the emulsion and so caused the re-duction in sensitiveness. Instead of adding the phenosafranine to the developer it cana

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