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Re: Gum vs. Kallitype
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>On Thu, 23 Mar 2000, Andre Fuhrmann wrote:
>> Permawash, I take it, is a washaid. Washaids usually contain soda. Soda
>> attacks gelatine. ... Glyoxal, however is not a very effective
>> hardener. My advice: Clear the gum print in alun (may take 30 minutes or
>> more) -- this will further harden the gelatine. Then let it rest for a
>> couple of days. Omit step 5 and extend step 6.
>
>Now just a darn minute, Andre -- you can't drop a line like that into our
>tea party & then take off. What's this about "glyoxal is not a very
>effective hardener"?
You gave the answer: not as effective as the common alternatives chrome
alum or formaldehyd. I shouldn't want to either confirm or deny that
length of hardening may be a factor. Seems we agree on the facts and I
apologize if my wording may have been misleading.
>As for "clearing gum" in alum. Consensus of conservators seems to be that
>alum bath degrades the color -- especially ye gods 30 minutes. (No I can't
>document, but have read 5,627 times.)
Depends on the color pigments. Alum does absolutely no harm to the more
stable pigments (eg earth pigments) that IMHO one _should_ prefer for gum
prints anyway. (I suspect that only a very few of the common pigments are
adversely affected by alum. Depends, of course, on what you count as
common.) Alum has the extra benefit of further hardening the gelatine
after the last print, thus actually contributing in one way to print
stability. (This is why I recommended it in the case at hand.) The real
drawback is that it is much harder to wash out than metabisulfite. But if
the washing time has to be extended anyway when you print a kallitype on
top, this particular disadvantage is of little consideration.
>HOWEVER, why clearing bath for gum anyway?
I understand that Keith used the washaid not for the dichromate for the
hypo that fixed the kallitype layer.
André