----- Original Message -----
From: "CarlosMFreaza" <cmfreaza@xxxxxxxxx>
To: <rollei_list@xxxxxxxxxxxxx>
Sent: Friday, February 17, 2012 10:46 AM
Subject: [rollei_list] Re: Expired in 1999
It could be interesting to add that the three or four frames
I
consider good to use regarding the expired film are from the
middle of
the roll to the end, perhaps this area was better protected,
someway.
Carlos
There are several mechanisms that cause film to
deteriorate with time but oxidation is one of them.
Generally, tightly wrapped film is less subject to oxidation
than if loosely wrapped. So, the film toward the center of a
spool will tend to have less effect from oxidation than the
film on the outside. Most of the fogging from old film
comes from a very slow continuation of the "ripening" effect
of the emulsion. The manufacturers got very good about
stopping this and extending the life of film without special
storage. The commonly heard explanation that the fog is
from radiation is true only for the fastest films and those
tend to have more chemical fog than slower films so its hard
to know what part of the fogging is from what source.
If old film is not badly fogged it can be exposed and
developed normally. There may be some lose of shadow detail
but the fog will tend to affect all densities the same way,
something like the anti-halation pigment in 35mm support.
One can compensate for it by exposing the film at perhaps
3/4 stop more than the rated speed calls for but that tends
to improve shadow detail anyway.
A fairly strong anti-foggant such as benzotriazole, can
eliminate the fogging and result in clear film where not
exposed but it also destroys some sensitivity so requires an
increase in exposure anyway. The negatives may look cleaner
but will not print any better.
Medium speed film like Plus-X or Verichrome Pan will
generally still perform pretty well ten years after it
expires provided it was not exposed to high temperatures
during storage. Low temperatures slow all chemical
reactions so freezing either B&W or color film will extend
its life substantially.
Film which has been exposed is subject to loss of the
latent image as well as fogging. Anti-fogging agents will
further destroy some of the latent image so should never be
used. There are special techniques for recovering the images
from film which was exposed long in the past. I don't know
the details of any of them but understand that one approach
is to use a very power developer, like a lithographic
developer, at very low temperatures.
I've used Verichrome Pan which was more than ten years
out of date with reasonably good results but not as good as
it was new. Again, the faster the film the more likely it is
to have become badly fogged. Also, the chemistry of film has
changed in the fairly recent past and I am not certain that
current product is as resistant to aging as it was perhaps
thirty years ago.
Color film has different effects from B&W although its
B&W silver film to start with. In order to reproduce color
well the contrast and range of the emulsions must match
properly, since those characteristics change with age old
color film will likely have color shifts well before it
becomes excessively fogged. The same comments with regard
to the loss of latent image with time apply to color film.
--
Richard Knoppow
Los Angeles
WB6KBL
dickburk@xxxxxxxxxxxxx
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