Re: Pyro redevelopment & Hardening


FotoDave@aol.com
Thu, 28 Jan 1999 14:59:01 -0500 (EST)


In a message dated 1/28/99 3:02:06 AM Pacific Standard Time,
cor@ruly46.medfac.leidenuniv.nl writes:

> On the whole I do not
> fully understand the term "hardening". I thought that hardening of
> negatives was ment to make them more resistant against scratches etc.
> Wheras hardening (with Glyoxal after gelatine sizing is ment to preventing
> consumption of the organic gelatine by micro-organisms. Seems to be
> different purposes...

Cor, the hardening of negative and size are based on the same principle though
as you said, the purposes might be different. Swollen unhardened gelatin melts
at around 40C. Hardened gelatine melts at near boiling point of water. Also,
hardened gelatin takes longer to swell (although given enough time it will
also swell).

While the prevention of consumption of gelatine by micro organism or insects
is an additional benefit, it is not the main purpose of hardening the size. If
that is the reason, the whole thing can be hardened after the print is
completed. The hardening of the size is so that the gelatin that is used in
sizing will no longer swell or melt when you further process the print (of
course, that is assuming one does not treat the paper or the size roughly
because "hardened" gelatin is actually quite soft). Also, if the gelatin is
not hardened, it will swell and bond with the gum coat, for example, and cause
staining in some case.

Dave S



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