[pure-silver] Re: Some Edwal Patents

Quoting "Nicholas O. Lindan" <nolindan@xxxxxxxxxxxxx>:

> "Richard Knoppow"
> > assigned to H&W and probably is for their "Control" 
> > It is USP 3,772,019
> 
> Which is phenidone with or without metol and
> hydroquinone.  Variations on POTA, but with
> magic claims.

The H&W Control is a little more than that-- albeit, of course, building
upon Marilyn Levy's work on "Wide Latitude Photography" (with the wellknown
POTA formulation)-- and some of the "claims" are hardly "magic". H&W Control
is NOT POTA just as not all MQ, PQ are alike or the same as their Ascorbic
counterparts. That's the thing about developers: subtle changes in Ph, buffer,
concentration, use/agitation and the addition of small amounts of reducing
substances can have a significant impact. That Levy was upset that Holden and
Weichert got a patent for work that she felt was not theirs is really another
set of issues (and we can side-track to talk about patents)..

Work in this area has continued and I should point out that  David Foy/Frugal
Photographer (Canada) sells modified H&W Control and POTA developers and
Heribert Schain/SPUR (Germany) designs and sells highly refined wide latitude
contrast control developers individually tuned for specific microfilms.

--- That all said.. the Edwal patents have long been well digested into many
other formulas, both public and proprietary. Still good reading..

- 
  E. Zimmermann, BSn/Munich R&D Unit
  http://www.nonmonotonic.net

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