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Re: Old sound tracks



Hi David,

That wonderful (?!?) vinegar smell is acetic acid, from the chemical
breakdown of the acetate base of the mag stock.  Old acetate film is
sometimes subject to the same deterioration.  Other symptoms include
shrinking and stiffening, which makes it run and pack poorly.  The vinegar
smell stops, by the way, after the film has been reduced to a small, sticky
mass that can only be broken off the reel.

If you have some reels that are going vinegary, it is very important to store
them away from good reels.  Over months or years, the acetic acid from the
bad reels can attack the good ones and cause them to start breaking down too.
 For the amounts encountered in old film, the acetic acid is not particularly
toxic to humans, but it is rough on the lungs, so people should avoid dealing
with this stuff in high concentrations.  They probably won't want to anyway!
 

Once a mag or film starts going vinegary, it cannot be stopped.  It is
possible, however, to slow it down a very great extent by keeping the
material as cold and dry as possible.  Before putting the stuff in the
deep-freeze, however, it should be dried.  Putting it in a lab oven at
120-130 degrees for several days usually helps; more or less time can be used
depending on how severe the problem is.  Indeed, I've "cured" mildly
vinegared film by simply leaving it out of the can, nearby (but not directly
on top of) a radiator.

I would not recommend putting vinegared mag stock through a film cleaner.
 There is a possibility that if the base is really beginning to deteriorate,
you'll get chunks of the mag coating flaking off.  Also, it probably won't do
much for the vinegar smell.

Cordially yours,
Christopher Bacon

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