> Judy wrote:
>
> >but the *emulsion* is not necessarily returned to the status quo ante. At
> >least I've always assumed that changes induced in the emulsion by heat
> >were probably permanent...
>
> Certainly not. I don't know of a single photographic process that is
> perfectly stable before exposure and development. Photographic
> manufacturers have spent hundreds of millions to come up with "stable"
Luis, I don't know what that "certainly not" refers to. What I meant was
that after heating an emulsion I would assume some changes had been
permanently installed, meaning it would not return to the condition prior
to heating, not necessarily that the emulsion was now stabilized (as for
instance paper might stabilize after wetting and heat drying a few times).
(You had commented that after a while *paper* which had been heated would
return to "normal" RH. Perhaps, but as far as I know, assume & have
observed, once you diddle an *emulsion* with heat, you can't go home again
-- wherever you do go, you're unlikely to be back on go.)
> With black and white papers, manufacturers have always had a helluva time
> manufacturing very high contrast paper, e.g., Agfa Grade#6, with a decent
> shelf life. Both Agfa and Ilford were fairly successful, but Kodak was not,
> at least with that kind of product.
I mention here, FWIW, that I have a supply of Brovira #6 FB which is in
the vicinity of 25 years old, still fine.
> Over the years I have run
> into research papers, patents, etc., that cover various improvements to
> make blueprint papers more stable before processing.
I've always wondered how they prepared commercial blue print paper to have
a shelf life of months (or more), as well as the Solargraphics kit,
which, although it gets pale, still makes an image after quite some
time. Do you know which stabilizers are used?
> want to keep an emulsion stable, cool it... In the conservation field, we
> teach that for each increase of 10 degrees the rate of deterioration
> doubles.
Aalthough such technical "deterioration" might in some cases be
"ripening."
As for Luis's "rules," let me add one more: Be open to gifts and
discoveries.
Cheers,
Judy
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