From: Christina Z. Anderson (zphoto@montana.net)
Date: 12/05/01-08:46:44 AM Z
Cool, Ted! I'm glad you offered your chem info. BTW, it is
"paraformaldehyde" that is sold, and it is in liquid and powder form. The
liquid is 37% and available in large sizes too (presumably for dead
bodies??)
When I was taught gum printing we used glyoxal, not formalin, because
of the toxicity of formalin. But then I read the thread on this list about
the yellowing over time of glyoxal (and can't remember what the final
decision as to this was) so now I am not so sure what to do.
Mordancage is a method of using copper chloride, hydrogen peroxide,
acetic acid, and immersing a normally enlarged BW print in this to
essentially eat away in various amounts the emulsion. You can leave some of
the disintegrated emulsion (which adheres tenuously to the edges between the
darks and highlights) on in waves or you can rub all the emulsion off the
print, and then in both cases redevelop in dilute developer or toner such as
sepia/thiocarbamide to get a positive, partially positive, or negative end
product.
Chris
----- Original Message -----
From: Ted Edkins <tedkins@cygnus.uwa.edu.au>
To: <alt-photo-process-l@sask.usask.ca>
Sent: Wednesday, December 05, 2001 2:21 AM
Subject: Gelatin hardening
> I have been lurking on this group for a few weeks as I am interested in
> making Pt/Pd prints and agyrotypes and wanted to pick up some tips.
> May I make a few comments to the gelatin hardening thread as I come from a
> background of biochemistry and work in a molecular genetics lab of a
> pathology department in Western Australia.
> There seems to be a problem in purchasing formalin in the USA although
> Christina said she bought some formaldehyde powder with no problem and it
> was cheap.
> As Liam pointed out formaldehyde is a gas and what is called formalin is a
> 37-40% solution in water together with some methanol to stop
> polymerisation. What Christina probably bought was paraformaldehyde, which
> gives formalin in solution when dissolved. The problem is knowing what
> concentration is in the solution as it stands and this will mean differing
> amounts of hardening at different times. (As an aside, I notice that the
> Merck Index lists paraformaldehyde as a component of spermicidal creams.
Of
> course it acts as a contraceptive, would you go near anybody using such a
> product?)
> Glyoxal can be used as Judy indicated but there is a problem with this as
> well. It's usually sold as a 40% solution and becomes very acid on
> standing, pH of around 1.5 to 2. In the lab it is often de-ionised and
then
> quickly frozen at -20 C; not the sort of thing for photographic use.
> The best bet is probably to use chrome alum or formalin, if you can get
it.
> This will give the best control from day-to-day compared to glyoxal or
> paraformaldehyde. (Not to be confused with paraldehyde; this was used to
> control mental patients in institutions for the insane; probably where we
> all should be in this age of digital photography.)
> By-the-way, what is mordancage?
>
> Edward 'Ted' Edkins
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