From: S Wang (stwang@direcTVinternet.com)
Date: 06/22/02-03:24:00 PM Z
Liam and Chris,
Thanks so much for the info! It's just what I needed!
And Mark apparently was extending an open invitation for me to use
his Imacon scanner (it does a fantastic job with negatives up to
5x7!). So I'll try the chemical methods first, knowing that I can
always ask Mark (and Photoshop) to rescue me if I screw up.
Sam
>Sam,
>
>With hydrochloric acid, dichromate bleaches silver to silver chloride, which
>is insoluble and redevelopable (as in chromium intensification). With
>sulphuric acid, the product is soluble silver sulphate that just goes into
>the solution, which is why it's used for reversal. Pot. ferri. bleaches to
>silver ferrocyanide, which can also be redeveloped, but it's very slow; it's
>usual to add some pot. bromide to speed things up... the result is then
>(insoluble) silver bromide. Any bleach giving an insoluble silver salt
>should be usable for negative reduction by bleaching and redevelopment.
>
>After bleaching, you need to redevelop or fix (or tone) for a stable result,
>since silver chloride, bromide, etc., are light-sensitive. A good way of
>reducing dense negs is the process known as *harmonising*, whereby you
>bleach fully in (e.g.) pot. ferri + pot. bromide, redevelop less than
>completely so that you get full shadow detail with reduced highlights, and
>then fix. The image will lighten more or less in the fix, and it takes a
>little experience to judge just how far redevelopment should go. For
>redevelopment, a print developer is probably best... conventional wisdom is
>that developers containing a high proportion of sulphite (e.g. D-76) may
>dissolve some of the silver salts before they can be redeveloped, but I
>can't say I've noticed it.
>
>
>Liam
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