>About 15 years ago (circa 1980), epidemiological studies were
>published which showed that formaldehyde caused nasopharyngeal
>cancer in human beings, which agrees with animal and in vitro
>test results. At the time, it was suggested that individuals
>working with it in labs confine use to fume hoods, and if
>possible, switch to less volatile crosslinking agents.
A good source on hardening of gelatin layers is:
'Making and Coating Photographic Emulsions' by Zelikman, Vitali and Levi.
(Focal Library) ISBN 0 317 09476 92051619. pp 266-275
There you will find a list of organic hardening agents that are thought to
act by forming cross linkages between neighbouring gelatin molecules. Among
these is a convenient and apparently safer alternative to the now notorious
formaldehyde, namely GLYOXAL, formula (CHO)2.
Glyoxal is available at modest cost (at least, from UK Chemical Supply
houses) as a 40% solution in water (just like formaldehyde), which only
has a slight odour (quite unlike formaldehyde). The health and safety
information that I have seen, states a toxicity for glyoxal far less than
that of formaldehyde, and glyoxal is said to have no known carcinogenic,
mutagenic or teratogenic properties. No exposure limits have yet been
assigned.
I have found a 1% aqueous solution of glyoxal (obtained by diluting the
stock solution 40 times) to be a very effective hardener of gelatine-sized
papers, just like formaldehyde, but without any of that substance's
obnoxious properties.
Since the hazards of glyoxal may not yet have been fully explored, I feel
compelled to add a disclaimer:-
This information is given in good faith for the benefit of members of the
Alternative Photographic Process List, but I cannot accept any
responsibility for injury resulting from its use.
Mike