[pure-silver] Some Edwal Patents

A mention of an Edwal developer in a recent post to rec.photo.darkroom reminded me to conduct a patent search for Edwal products. I found two Edwal patents which may be of interest. One is Edmund Lowe's patent for extra-fine-grain developers. He gives examples of developers containing Ammonium Chloride as the fine grain agent. Since Microdol-X and Perceptol are similar types but using Sodium Chloride I think this patent is of considerable interest. It is USP 2,164,280 The other patent is a later one for general fine grain developers using Metol and Glycin. It is USP 2,374,921 Another patent that showed up in the search is one assigned to H&W and probably is for their "Control" developer for high contrast film. H&W sold a microfilm type film for super-fine-grain pictorial use under the name H&W Control with a special pictorial contrast developer. This is similar to Kodak's Technical Pan and Technidol. The developer may still be of interest for those who want to use thin emulsion microfilm for pictoral purposes. 
It is USP 3,772,019


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Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx 
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