[pure-silver] Re: PMK and MCS
- From: Ryuji Suzuki <rs@xxxxxxxxxxxxxxx>
- To: pure-silver@xxxxxxxxxxxxx, dfoy@xxxxxxxx
- Date: Fri, 28 Apr 2006 15:03:15 -0400 (EDT)
From: David Foy <dfoy@xxxxxxxx>
Subject: [pure-silver] Re: PMK and MCS
Date: Fri, 28 Apr 2006 09:35:58 -0600
> I read and re-read and re-read Anchell and Troop, who I believe
> popularized the idea of avoiding acid fixation, to try and find out why
> they advocate against it. The only thing that I could find were
> suggestions tucked away here and there that modern films have higher
> iodine content than earlier films, and there is apparently something
> about this, having to do with how long things take, perhaps too long
> wash times, that lies behind the preference for alkaline processes
> straight through from start to finish. Perhaps I missed something. I
> know of no professional photochemist who sees it as an issue.
Don't try to make much sense out of that book. (In my previous post, I
implicitly said this.)
That modern emulsions contain "higher" iodide content may or may not
be true. In old technology, the amount of iodide changed a lot of
variables and emulsion engineers didn't have much freedom. But today's
emulsion engineers can design grain structure in multiple layers, and
the thin ones are only a few molecules thick. The place and amount of
iodide within crystal structure has great influence in efficiency of
making latent image centers, efficiency of spectral sensitization,
etc., but these have nothing to do with acid v. alkaline fix process.
In research of image permanence, it is often important to test with
two kinds of emulsions, one with iodide and the other without any
iodide. Emulsions containing no iodide are usually more vulnerable to
oxidative attacks unless some other means of protection is given to
the silver image. Again, this is irrelevant to acid v. alkaline fix
debate.
While I believe there are some advantages to neutral to weakly
alkaline fixing bath for b&w processing, many debates on the topic are
on unfounded basis.
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