From: Ted Edkins (tedkins@cygnus.uwa.edu.au)
Date: 12/05/01-03:21:57 AM Z
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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