From: Judy Seigel (firstname.lastname@example.org)
Date: 07/04/02-12:06:13 AM Z
On Wed, 3 Jul 2002, Breukel, C (HKG) wrote:
> I ofcourse did pre-shrunk (per PF instructions).., but I tested a
> size/hardening in one step (solute gelatine 1.4%, than boil it with 1
> gram Alum per 500 ml, cool down and brush it on the paper).
Cor, I hesitate to even mention this because you are the lab king -- but
you are BOILING gelatin? I was taught (& every source I've seen says
that) boiling gelatin "breaks it down." When students have gotten a
mysterioso pitting in a gum coat, 99% of the time it turns out to be from
the sizing, and that generally turns out to be from scalding the sized
paper with boiling water (from the tap !), which kills the gelatin, or
cooking the gelatin too hot before coating it.
> BTW2: it is probably worth noting that the dichromate in the gum mixture
> did NOT bleach away the silver image of the Kallitype: Simple theory:
> the silver image is more in the paper fibers, wheras the gum layer
> stastays more "on top" of the paper fibers..
The size went on over or under the kallitype? If it's over the kallitype,
maybe it protects it -- or maybe boiling gelatin in alum trumps
dichromate? But other people have, come to think of it, mentioned using
gum over kalli successfully. Is it possible that the relatively small
proportion of dichromate with pigment and gum arabic added mitigates the
action of the dichromate as bleach???
I haven't done gum over kallitype, but did do cyano -- which bleached the
kallitype about half way -- maybe potassium ferricyanide is stronger in
that respect than k di???
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