File:The American annual of photography (1922) (14595013948).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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2 drams of Bichromate you will find 10 to 12minims of, say the Velvet Black about right. This color isliquid being mixed with water and Glycerine. When the paperis coated it should appear a rather light, yellowish brown. Inlater printings you can use more pigment and it should butrarely be necessary to make more than four printings to geta scale ranging from the deepest blacks to white. Print in direct sunlight and try an exposure of twentyminutes in the middle of the day. Be careful not to exposethe paper to too strong a light when putting it in the frameor removing it as it is quite sensitive. The paper after ex-posure will show you quite a clear image if your coating hasbeen light, but while it is possible to judge quite accuratelyby this image whether your printing is sufficient it requirespractice and experience, so at first you had best simply exposefor a certain length of time and then develop the print, andone or two trials will quickly give you the correct printing time. 130
Text Appearing After Image:
J. ANTHONY BILL. 131 The whole principle of Gum Printing can be very simplystated. It is, that a colloid, in this case Gum Arabic whichhas been rendered more or less insoluble by the action oflight on a sensitive salt such as Ammonium Bichromate holdsthe pigment on the surface of the paper in a greater or lesserdegree depending on the extent to which the Gum has becomeinsolubilized, hence the development of a print consists in wash-ing off the pigment which has not become attached to the paperby the light action. A printed piece of paper may be developeaautomatically by immersing it in water, face downward, andleaving it until the pigment has washed off the paper. I donot advise automatic development, however, as working thisway one has no opportunity for personal control and modi-fications of the image and values, which of course it is neces-sary for the pictorial worker to have. As I said before, printuntil after soaking in water until Hmp the color will beginto leave the paper upon

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