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Re: Hardening gelatine, pigments for gum
On Mon, 27 Mar 2000, Andre Fuhrmann wrote:
> Hello Judy,>
> let's try sorting this out. I claimed, that glyoxal is probably not as
> effective an hardening agent for gelatine as chrome alum or formaldehyde.
> By "not as effective as" I principally mean that glyoxal-hardened gelatine
> is less resistant to high temperatures and/or physical abrasion as the
> alternatives. My source is "hearsay": a professional chemist told me. He
> and a fortiori I may well be wrong. But not being a chemist myself, I
> wouldn't know how to set up and interpret reliably an experiment.
Andre, I really appreciate this discussion because it brings us close to
the problems we have in using these chemicals for our own purposes, tho
not necessarily to the answers...
In my experience very few reports from generalists are definitive -- after
all, if different chemicals didn't work better for some things than
others, only one would be on market... Maybe, if you know how to use it
properly, the formaldehyde really is *better* -- tho for me a really major
factor is being able to harden without pain & suffering ... or dislocation
-- the formaldehyde fumes made the studio intolerable just in outgassing
from paper fully dried the day before outdoors !! Burning of nose and
throat was so serious I had to remove it for another 2 days...
But I try to avoid "common sense" -- or the "seems-logical disease in
gum." Paul Anderson did this and came up with several fallacies which
suffused gum printing since 1930, enshrined in the canon, from Henney &
Dudley, cut & pasted (withOUT testing !!) through Crawford, Scopick, and
now the so-called "Ansel Adams Guide II." I've addressed some in print
(first 3 issues of Post-Factory), so let one example suffice here:
Anderson made it axiomatic that the more pigment in the emulsion, the
greater the range of possible tones. One test showed that doubling the
pigment actually cut down the tones in normal printing as the shadows
blocked up. (P-F Issue #2.) Which is not to say that an adroit printer
couldn't possibly get a longer scale by looooooong development, but no
guarantee either, because depending on the mix & the paper, top tones
could wash off as fast as lower ones appear.
This is of course entirely different with digital negs for gum. I speak
here only of SG continuous tone.
> Apparently, you did some testing yourself and found glyoxal at least as
> good as, perhaps even better than ChrAl or FdH. What I do not dispute is
> that for common gum printing the three candidates for hardening are
In light of further knowledge of possible variables, I'd say my tests were
rudimentary -- but they showed that one day after hardening, the glyoxal-
hardened paper stained less than same emulsion on formaldehyde-hardened
paper. Maybe the following week, or month, all would have been equal --
but the glyoxal being so much easier to get here and use (not just at
home, even more important in school !), it seemed enough. Heat is not
much of an issue because really hot water can harm any gelatin ... tho
longevity of the gelatin is important. I'm told, BTW, that an alkali added
to either hardener makes the links of the gelatin stronger -- but found
adding most alkalis to the glyoxal discolored it...
> probably all good enough. But our little discussion was sparked off by a
> case where gelatine is being subjected to some extra pressure (i.e. soda).
I spilled a soda all over my lap in a restaurant Saturday night --
fortunately not on my gum prints.... Ha ha. But as I recall, that soda
you speak of was for a final clearing. My suggestion if in doubt would be
another hardening BEFORE clearing bath, to be on safe side & easy
enough...
The problem with,
> Heinrich K"uhn used mostly earth pigments for his gum prints and cleared
> with alum (as apparently most of his contemporaries). I don't know what
his
> prints looked like 100 years ago but they still look good enough to
me. He
> was a dedicated amateur chemist and had a very discerning eye. If he
> didn't complain of a degrading of colours during the alum bath, I shan't
> either.
is that I don't know which colors he used, and even if I did, couldn't get
them today because those colors are mined out -- often as not manufactured
substitutes are used (according to Artists Equity newsletter & other
sources), and even if not -- the next row of Italian hills can have a
quite different chemical composition.... As I mentioned, for instance,
when I first began gum, I bought 6 brands of "burnt sienna." Each turned
out to be a different color, different covering power, & worked
differently. I made the mistake of assuming that because Rowney burnt
sienna was best, all their colors would be best -- and laid in Rowney.
Not so.
I found further that in many colors brands that are are even NOMINALLY the
same color, that is, have the same chemical name, not only have different
additives, but can have intensity so much weaker you have to use so much
paint to get the color strength, the emulsion works differently, etc. etc.
etc.
Which is to say, generalizations & common sense are (at least around
here) a booby trap.
I'll add that on the few occasions when I had to use a sulfite clearing
bath, I didn't NOTICE any harm to the print -- but what I am noticing
today is that an added coat of gelatin after several coats seems to deaden
the print, at least on the smooth papers I prefer -- and of course it's
just the prints one cares the most about where one takes trouble to
re-gelatin in progress.
So I'm wondering if formaldehyded gelatin might actually last longer -- as
I recall it didn't, but TESTING that out is a REALLY arduous operation --
and even then might apply only to the given paper and gum !! (Anyone want
extra credit on a phD?)
best,
Judy