Herold Faulkner (faulkner@redshift.com)
Fri, 12 Feb 1999 23:19:07 -0800
Foto Dave asked:
"Will the bleach in C-41 process or the bleach in 6-step E-6 process work?"
Dave,
I doubt very much that E-6 bleach will work for b/w reversal processing. It
is a different animal altogether from the b/w reversal processing bleaches.
It has been a while since I ran an E-6 line but as I recall the bleach is
iron based and occurs after the color developer. The trick in E-6 is to
remove all the silver from the film and hence the bleaching action is quite
different.
In the early 90's one of the popular mags did an article on reversal
processing in which gave formulae for several different bleaches. I can't
tell you much more than that at the moment but if pressed I might be able to
locate my reference. Kodak's T-MAX100 direct positive kit initially used a
chromium bleach but was later reformulated to use a permanganate bleach.
There were some complaints at the time that it didn't give as good a Dmax
but I never ran any tests. At the time Sprint offered chemistry for
reversal processing of b/w films and it was considerably more economical
than Kodak's kit.
BTW the chromo-sulfuric bleaches are considered quite hazardous and should
not be dumped in the sewage system. Years ago in Minneapolis I was told by
local pollution control agency personnel that disposal of hexavalent
chromium (YELLOW) is a no-no. However, if the bleach were neutralized by
sodium sulfite 'till it turned a kind of yucky green it was tri-valent and
was NOT hazardous. Hence I always neutralized my bleach with the clearing
agent after use before disposal.
Hal
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