"zach" wrote in message
...
On Mar 28, 4:57 am, "
wrote:
How long does Agfa MCC last at room temperature?

I just purchased a batch thats around 5 years old.

Regards

Bob McCarthy

I think the biggest factor to aging is from neutrons emitted
from the
sun. kodak had/has an under ground site under ?Lake Erie?
that has the
density to block most of these wave lengths. Freezing slows
chemical
reactions so it may help reduce the prior effect...Sorry I
don't have
more specifics. I too have used 3+ year old paper with
acceptable
results and those without.

Not sure if you mean neutrons but some cosmic rays can
affect the fastest emulsions. In general paper emulsions are
too slow to be fogged from this cause. Most fogging is
caused by a contuation of the chemical process by which the
silver halide crystals become more sensitive in manufacture.
This process is called ripening. While it was done by slow
cooking of the emulsion in the past it is now done on a
continuous basis by chemical additions. With either method
other chemicals are added to stop the process when it
progresses as far as desired. However, the ripening
processes never stops completely and some "fog" crystals are
produced. These halide crystals will develop into metallic
silver without exposure. They are undesirable but inevitable
results of the ripening process. Emulsions contain
anti-fogging agents and stabilizers to prevent the
generation of fog crystals but they will eventually be
produced. This is only one of the chemical processes in the
emulsion which continue to some degree after manufacture and
which cause fog. Oxidation at the surface of the emulsion is
another cause of fog but unopened packages of paper or film
are not likely to suffer much from this.
Since all chemical processes are increased by
temperature storing sensitive materials at low temperatures
is desirable for long shelf-life.
Some of the stabilizers used in the past, for instance
cadmium, are no longer used because they present an
envirionmental hazard, as a result, film and paper
manufactured in the last about decade do not have as long a
shelf life as in the past.
It appears that variable contrast paper, for various
reasons, is not as long lived as graded paper, but warm
toned emulsions also seem to suffer more from age than cold
tone ones, perhaps because of the fineness of the grain.
Paper which is only moderately fogged can often be
salvaged by using benzotriazole in the developer.
Benzotriazole is a powerful anti-fog angent, more effecitve
than bromide when used in photographic developers, and has
relatively less effect on emulsion speed. Either
benzotriazole or bromide will affect speed, image color, and
characteristic curve, to some degree depending on the nature
of the material and the amount used.


--
--
Richard Knoppow
Los Angeles, CA, USA