Liam Lawless (lawless@vignette.freeserve.co.uk)
Sun, 24 Jan 1999 17:43:38 +0000
Hi Sandy,
The test that I reported yesterday was on a (reject) APH neg that I'd made
by reversal, using an ordinary developer. Bleaching and redeveloping in PMK
pushed up the maxiumum density from 2.44 to 3.17, or 3.21 after the used
developer afterbath. I didn't bother looking at other densities because at
the time I only wanted to know if intensification was in fact occurring.
I'm no chemist (failed my chemistry 'O' level miserably), but I believe that
bleaching in pot. dich. and hydrochloric gives silver chloride and an
insoluble chromium salt that is responsible for the intensification. With
bromide added, my guess is that you would be producing silver bromide
instead of silver chloride (because the bromide is more insoluble), whch
would redevelop in much the same way, so it would appear that it doesn't
perform any useful function at all. That's what I think anyway, but maybe
someone out there can give you a better answer.
Perhaps the reason you're not getting a density increase is some strange
incompatability between pyro and chromium. Try ferricyanide-bromide: I'm
convinced that works.
Liam
-----Original Message-----
From: Sandy King <sanking@hubcap.clemson.edu>
To: Liam Lawless <lawless@vignette.freeserve.co.uk>
Date: 24 January 1999 05:26
Subject: Re: Pyro redevelopment
>>Hang on a minute, chaps, we're all missing something here: of course
>>bleaching a straight neg and redeveloping in PMK will intensify! A good
PMK
>>neg tends to be thinner than an ordinary neg, but its overall density is
>>determined much less by the developer than the development time; allowed
>>enough time to act, it will develop all silver that is developable. With
a
>>bleached neg, it will therefore redevelop all of the original silver
within
>>10, 15 minutes or whatever, AND add its stain to it. Result? An
>>intensified neg!
>
>Absolutely. However, I am interested to see what results you get bleaching
>a *reversal* negative and then re-developing. If your results indicate the
>possiblity of significantly increasing the contrast of such negatives then
>I will have to re-think my previously expressed premise.
>>
>>This still doesn't explain Sandy's results. As a matter of interest,
Sandy,
>>why is there bromide in your bleach?
>
>Quite frankly I don't know exactly what the bromide does but it is
>recommended in the formula of several super proportional reducers that I
>have on hand. I am going to assume that its primary function is to restrain
>the heavier silver deposits and reduce overall density, but this is only
>speculation.
>
>Sandy King
>
>>
>>
>>Liam
>
>
>
>
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