----- Original Message -----
From: "Koch, Gerald" <gkoch02@xxxxxxxxxx>
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Thursday, October 13, 2005 10:45 AM
Subject: [pure-silver] Re: expiration dates on film boxes
Professional film is treated differently from amateur film,
at least by
Kodak. Professional films are held after manufacture until
their
sensitivity and contrast match a standard. Then they are
released for
sale. Thus a film like TXP is not "fresh from the factory"
but it is at
a certain known point in its life cycle. This is to insure
consistency
between runs. In contrast, amateur films are released
almost
immediately after manufacture.
I don't think this is true of B&W film. Kodak states that
this is true for color films. Amateur films are made such
that the balance and other characteristics are acceptable
when fresh and at the expiration date and drift through an
optimum at some point in time. Professional films are
intended to be stored under refrigeration until use and are
designed to have optimum and reproducable balance at the
time of purchase. Dealers for the pro products are required
to refrigerate them under conditions specified by Kodak.
The main issue is color balance which is affected by even
slight changes of speed and especially curve shape of the
individual layers of the emulsion. B&W film does not have
this problem and is in all ways less critical.
Some Kodak "pro" B&W films have retouching surfaces on
both sides where the amateur film does not.
My own experience is that longevity is very brand
dependant. For instance, I have a lot of Plus-X sheet film
which was bought outdated perhaps 15 years ago. I also have
some Agfa APX-10 sheet film which was bought new perhaps 12
years ago. The Plus-X has become slightly foggy. A small
amount of bromide added to the developer results in
completely clear film edges. The APX-100 is much more foggy.
I have not yet tested it with a large dose of bromide but I
think it may be unusable.
---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
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