File:The American annual of photography (1919) (14595801439).jpg

Identifier: americanannualof3334newy (find matches)
Title: The American annual of photography
Year: 1919 (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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e latent image is fullydeveloped fog still continues to form. An ideal developer istherefore one which gives the maximum contrast before theemulsion begins to fog, and such a developer can only be foundby trial with the particular emulsion used. As mentioned above,paraminophenol (Kodelon) most nearly approaches this idealcondition with negative emulsions, even at temperatures above70° F. Methods of Compensating for Chemical Fog. (a) The amount of fog produced by a developer may be re-duced by adding a soluble bromide or iodide to the developerbefore use. The precise action of a salt like potassium bromideis not thoroughly understood though it may be explained fromphysico-chemical considerations, the added bromide diminish-ing the solubility product of the silver bromide which is aboutto be developed. Potassium iodide probably converts a por-tion of the silver bromide grains to silver iodide, which de-velops with difficulty. (b) If the emulsion tends to give fog this may be compen- 34
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THE LURE OF THE STREAM. JAMES N. DOOLITTLE. sated for by adding bromide or iodide to the developer asabove, though in the case of photographic paper the color ofthe developed image is affected. It is also possible to treat gaslight paper in a bath consistingof a mixture of potassium bichromate and sodium chloride,afterwards washing and drying, thereby converting any foggedsilver grains to the unfogged condition, though the processdiminishes the general light sensitiveness of the emulsion.Dichroic Fog. This is a particular kind of fog which occurs only on nega-tive plates, films, and lantern slides as a more or less uniformveil over the gelatine coating. When examined by reflectedlight the deposit appears yellowish green while by transmittedlight it appears reddish pink, hence the name dichroic fogwhich means two-colored fog. When examined under the ultra microscope the fog is seento consist of ultra microscopic particles, which by chemicalanalysis have been shown to consist of metalli

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