Proof paper simplifies the teaching of photographic chemistry - Journal

Proof Paper Simplifies the Teaching of Photographic Chemistry The processing of photographic prints is difficult in a chemistry lab because of the need for near total darkness. This problem can he eliminated by using Studio Proof Paper which is sensitive only to ultraviolet radiation (as in sunlight) and can thus be safely handled in a elassroam with the window hlinds pulled down. This paper may not be stocked by many retail photo dealers but they can order i t for you. A further advantage of proof paper is that no chemical developer is needed. Prints may be fixed by emersion in a 10% sodium thiasulfate solution followed by washing and drying. The following lab procedure serves as an introduction t o the chemistry of photography. Two or three lab groups will be assigned the job of preparing 200 ml of 10%sodium thiasulfate solution to he used as a fixing bath by the rest of the class. A print is prepared by placing a sheet of proof paper with the shiny emulsion side facing up on a hook. Negatives or other objects are arranged on top of the paper (fern and other leaves work well). A large glass plate is pressed dawn firmly to keep everything in place. This setup is carried outdoors and exposed to sunlight for about 5 min. The exposed paper turns to a dark purple which fades to dark brown when the print is returned to the ish and fixed. Fixing should he followed by washing for several minutes. Excess water is blotted off and the print should be allowed to dry with the emulsion side exposed to the air.

Ouestions 1 ) Is your print a positive or negative? 2) What chemical reaction caused the paper to darken? 3) What would happen to an unfixed print? 4) How does the fixer make the print permanent? Senior High School Mechaniesburg, Pennsylvania 170.55

Richard K. P u t t

Volume 53. Number 3. March 1976 / 171