Kurt Seefeldt (seefeldt@s.imap.itd.umich.edu)
Thu, 11 Mar 1999 08:50:50 -0500
-----Original Message-----
From: Liam Lawless <lawless@vignette.freeserve.co.uk>
[snip]
>Copper sulphate + citric acid does not bleach on its own, or if it
does it
>does so so slowly that I couldn't see it. With hydrogen peroxide
added, the
>film (a finished neg) was a fraction lighter after nearly two hours,
but
>this is probably a bit slower than we want. I didn't try adding
nitric as
>an accelerator because the point is to avoid not only sulphuric, but
equally
>evil substitutes.
>
>Pot. permanganate + sod. chloride + acetic does bleach - very
quickly - but
>leaves a fairly strong orange-brown residual image which does not
clear
>(clear in 5% sod./pot. metabisulphite, though 5% sod. sulphite also
seems to
>work). This, I believe, is permanganate-stained silver chloride, as
it can
>be redeveloped.
> [additional details deleted]
I read an old booklet the other week with some formulas for reducers
and remember seeing the use of "a few drops of ammonia in a tray of
water" to clear either chromate or permanganate stains (I can't
remember which one). It gave a clearing time of "a few seconds". I
think it was the typical household ammonia. The language suggested
that this is not the optimum procedure, but rather a last resort.
Again, I can't remember whether it was for chromate or permanganate
clearing. Sorry.
I'm hoping to actually finish my dark room (aka basement bathroom) so
I can try this reversal processing. I got the chemicals early last
week, now all I need is to get the package of spare time that I
ordered a while back (it was on backorder).
- Kurt
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