Readily Produced Black and White Positive Slides Capable of Continuous Tone Rendition Recent articles by Rroukr et al.' and by Hamer e t presented methods of obtaining positive black and white slides. The former described a h i ~ hcontra41 material which required special treatment fur continuuus tone rendltiun and which is available only in hertofoot rolls, whde the larwr involves thirteen stops uf pruresring. Each involves some 20 min of darkroom time. There is another method, which readily produces continuous tone positive slides from monochrome materials, which is described by H ~ l l a n d e rI. t~uses a film designed for duplicating medical X-ray photographs: Kodak Rapid Processing Copy Film SO-185. Development in an X-ray film developer takes 1% minutes, and all four steps of processing are accomplished in less than ten minutes. Drying is rapid due to the thin emulsion. Resolution is excellent. Like the method of Brooks et sl.', long exposures are required, so that a vibration-free copy stand is necessary. Further, the emulsion is not panchromatic and may give false tonal values when used for colored copy. These disadvantages may well be outweighed, in many applications, by the ease of processing, continuous tone capability, and availability (in 36 exposme cassettes obtained as special orders through photographic dealers) ofthis film.
'B m k .
D, W.. Hedgss. R M..and Phiilen.D. I,. J.CHEM. EDUC.. 50,566, (19631. 2Hamcr, N. Tagl, L.,and T d i f , J., J. CHEM. EDUC., 52, C17,(1975). Hol1ander.S.. AudiovisuolInalrurtion, 19.83, (November 1974).
Indiana-Purdue University Fort Wayne, Indiana 46805
116 / Journal of Chemical Education
D. P. Onwood
