From: Judy Seigel (email@example.com)
Date: 02/05/00-01:18:58 AM Z
On Fri, 4 Feb 2000, Ray Rogers wrote:
> Of course,the word 'Glue' is used in a more general
> way, I admit, but to say that PVA is a major component
> of 'glue' is a bit stretching I think.
> In any case, I wouldn't want to call a PVA print A GUM
> print...It would sound dishonest. Well, at the least,
> misleading and inaccurate.
Ray, the plot thickens, as it were, because GLOY is labelled "Gloy
Gum," and it is a glue... so.......
My understanding is that Gloy has colorants and emulsifiers added to the
PVA. I myself have no problem with calling a Gloy or PVA print a gum
print, in the same way we might call a photo copy a "xerox" even if it was
made on a Canon. The gloy or PVA prints I've seen were basically made
like gum prints OF A SORT, and LOOK like gum prints, that is to say rather
crude gum prints, at least *the ones I saw* were not delicate as gum can
be, but could not be identified otherwise as done with Gloy.
Which is to say calling them PVA prints strikes me as a needless
complication... also an invitation to obfuscation: dealers touting one or
the other, that's a gum print, that's a PVA print (superior/inferior), and
then some poor schnook 50 years from now falls in love with one and can't
find out what this PVA print is, because it's not in ANY book. Etc.
But speaking of PVA, I happened today by cosmic coincidence to come across
an e-mail from Klaus Pollmeier to the list dated Feb 27, 1996, when I was
looking for something else (which I didn't find, needless to say).
QUOTE Klaus Pollmeier:
There are probably even more types of PVA than types of gelatin, with even
stranger physical/chemical properties.
The water solubility of Polyvinyl alcohol depends on its degree of
polymerisation. The higher the degree, the lower the solubility.
The content of PVA also has an influence: With more than 5% it becomes
insoluble in cold water, but soluble at 65-70 deg. C. With 20% it is
soluble only at 35-40 deg. C., & will stay liquid even while cooling
down. With 40% it is soluble at room temp, but falls out at 30-35
deg. C. With more than 50% PVA content is insoluble in water.
[Note: those figures look backwards to me, but are as written]
.... developing dichromated PVA coatings will be easier if 0.5% ammonium
thiocyanate is added to the PVA. Even overexposure or tanning caused by
too long waiting before development can be compensated by a little
thiocyanote in the dev. water....
So maybe the Brits have naturally occurring ammonium thiocyanate in their
tap water, which explains their ability to develop Gloy. Above could also
explain why Randall develops his prints in hot water.... and if anyone
feels bound & determined to import expensive Gloy to the US, maybe they
could make it work with some thiocyanate.
| Judy Seigel, Editor >
| World Journal of Post-Factory Photography > "HOW-TO and WHY"
| firstname.lastname@example.org >
> > That said
I am not currently a gum printer and cannot > speak for others who are.
> What, friends and colleagues, is your opinion?
> Would it be correct to call a PVA print a GUM print?
> Would 'PVA print' be preferable?
> What about 'Synthetic' or 'Artificial' GUM print?
> If gum printing is going synthetic, is it time for a
> better name?
> Do You Yahoo!?
> Talk to your friends online with Yahoo! Messenger.
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