From: Ryuji Suzuki (rs@silvergrain.org)
Date: 07/22/03-11:47:16 PM Z
From: Nigel Miller <nm1@bolton.ac.uk>
Subject: Liquid light questions
Date: Tue, 22 Jul 2003 18:20:35 +0100
> One solution David is trying (as we speak) is to pre coat the
> watercolour paper with a gelatine solution hardened with Chrome Alum
> but this has produced its own interesting (but annoying) effect. The
> print now darkens significantly when it is at the fixing stage, it
> doesn't look fogged it just looks like it has had too much initial
> exposure. David is also using Chrome Alum as an additive to the
> Liquid Light emulsion but as well as the darkening effect in the
> fixer the emulsion is still lifting off.
Unfortunately, none of these is the fundamental solution...
> We are aware that we are using more than the recommended amount of
> Liquid Light per print but this has worked so well with smaller
> prints and reducing the amount of liquid light produces a poorer
> print (blacks etc).
It is best to coat paper with undiluted, viscous, gummy emulsion.
> Does anybody have any suggestions?
The problem you are seeing is a common problem with old emulsions and
homemade emulsions.
Unhardened gelatin swells in water, but this swelling increases as the
solution's pH increases. At some point, gelatin's shear and abrative
strength may become inacceptably low, or other mechanical distortion
presents problems like yours.
The common solution is to use hardener. Traditionally, fixing bath is
acidic, and alum hardeners are used. The problem is that alum hardener
loses hardening effect once the gelatin is transferred to an alkaline
environment. In plain print processing, fixing bath is followed by
washing process, so this is not a problem.
Brown toner (polysulfide), selenium toner, thiourea indirect toner,
etc. requires very alkaline environment, and these baths will undo the
hardening action and promote gelatin swelling. This is the problem you
are seeing here. Lith developers are also quite high in pH and low in
salt concentration when diluted for lith printing purposes. The same
problem occurs.
The solution is to use one of aldehyde hardeners. I think MACO sells a
paraformaldehyde hardner. Glyoxal is another hardening agent commonly
used in alt processors that can be used for silver gelatin process.
These hardeners can be used by mixing to emulsion immediately before
coating, in a bath preceeding developer, or mixed into developer.
Hope this helps.
R
-- Ryuji Suzuki "Reality has always had too many heads." (Bob Dylan, Cold Irons Bound, 1997)
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