From: Richard Knoppow (dickburk@ix.netcom.com)
Date: 05/09/00-06:26:16 PM Z
At 03:38 PM 05/09/2000 -0400, you wrote:
>
>On Tue, 9 May 2000, Nick Makris wrote:
>
>> I once found a roll of exposed VPS 120 in the trunk of my car - I had it
>> developed and it turned out to be a roll from a trip almost 6 years prior.
>> No noticable degradation.
>
>I understand that color film for civilians (ie amateur use), is made so
>that it "keeps" well, assuming it will sit a long time in the camera (tho
>not necessarily 18 years), while professional color film is already
>"ripe", therefore kept refrigerated.
>
>I'm wondering if this difference might not obtain between black & white
>roll & black & white sheet film? I know that a friend tested -- I think
>it was T-Max -- and found a change in exposed film in just a day or so. Of
>course he was (is) a fanatic, and those changes might be insignificant to
>most users.
>
>However, there is a difference being glossed over here: "Shelf life" of
>the film before exposure is not the same as AFTER exposure. Those
>sensitivity specks and their family, once they've been called forth, will
>change... studies in latensification touch on this.
>
>So Chris, depending on how soon you're going & how generous your tolerance
>is, you probably could run a test now of a gray scale, & develop .... at
>whatever intervals seem likely, to allow for duration of the trip. It's
>even possible you might get a handle on change of exposure or development
>as the trip progresses...
>
>Judy
The issue for color film is the matching of the emulsions. For the color
rendition to be good the curves of the three emulsions must match pretty
closely or there will be color shifts of a sort that are not easily
correctible. The contrast of the emulsions drifts slowly with time. This is
not an issue for B&W is is critical for color.
You are right about the difference between Kodak's professional and
standard color films. The stuff for amateurs is allowed to drift through
its optimum match at some period of time after manufacture. The Pro stuff
is set for a perfect match at the time of manufacture and must be kept
referigerated to prevent further drift.
Processing should also be done quickly since the contrast drift will
continue after exposure plus the latent image will change. Again, this is
not an issue for B&W so refrigerated storage is not important for this
reason although it may improve storage life.
Latent image stability has been the subject of extensive research. Its
important for both B&W and color films but especially for color as detailed
above. Modern film is very stable. However, the latent image will tend to
become degraded with time plus there is the usual fogging of the unexposed
halide from cosmic rays and chemical changes. Freezing of film tends to
reduce both fogging and loss of latent image but is necessary only for very
long storage.
There is not much difference between roll and sheet films. Sheet film is
usually coated on a much thicker support than roll or 35mm film. There may
also be differences in the anti abrasion super coating and in back coating.
All standard roll films are back coated to reduce curling. The super coat
is to protect the emulsion. Both sides may be coated to make them suitable
for retouching.
The differences in emulsion depend on the manufacturer. Kodak has a bad
habit of selling quite different emulsions under nearly the same name. In
the case of Tri-X both emulsions are available in 120 so the confusion is
even more.
---- Richard Knoppow Los Angeles,Ca. dickburk@ix.netcom.com
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