File:The American annual of photography (1912) (14762724571).jpg

Identifier: americanannualof1912newy (find matches)
Title: The American annual of photography
Year: 1912 (1910s)
Authors:
Subjects: Photography
Publisher: New York : Tennant and Ward
Contributing Library: Harold B. Lee Library
Digitizing Sponsor: Brigham Young University

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eed to a definite distance into the film, becausethe tanning action itself prevents its own progress throughthe film. If too much acid is used the progress of the in-solubilizing action will be arrested on the surface of thefilm and a thin, poorly colored, strongly tanned, image willresult. The whole process, therefore, depends upon the degree ofoxidation, and the best pictures are produced by a certainprearranged quantity of acid which will allow the tanningaction to proceed at a definite rate through the pigmentedgelatine film. The simplest method of adding the acid is tofirst soak the plaster in the diluted ozobrome solution andthen to immerse it in the acid solution of a definite strengthfor a definite time, say 15 seconds for a good correctly exposedand developed bromide print from a good negative. Six toten seconds immersion would probably be sufficient if a grayor weak bromide print is required to give a more contrastyozobrome, and in dealing with a bromide print presenting 194
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BEAVER BOY, SIOUX. Copyright 1908 by J. A. Johnson, strong shadows and harsh contrasts 20 to 25 seconds immer-sion in the acid bath may be given to reduce contrasts. Avery convenient way of using the acid bath is to dilute itwith an equal volume of water, thus halving its strength andto give it double the time of immersion. This is particularlyrecommended in manipulating large prints, and it is advisablefor beginners to adopt the half strength bath for the simplereason that it is found the inexperienced worker generallyoversteps the mark with regard to time. The acid bath which has been found to work efficiently anduniformly is: Water 1000 c.c. Chrome alum (pure) 15 grammes Bisulphate of potash 5 Citric acid 2 The bisulphate of potash should not be confounded with thebisulphite of potash, which will not do at all. Oxidizing acids alone, such as sulphuric, hydrochloric andnitric, are apt to produce free bromine, and if used at all shouldbe used fresh for every two prints. The proportio

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