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Re: [ARSCLIST] Acetate tape discolours tape box
From: Patent Tactics, George Brock-Nannestad
Bev Lambert wrote a bit down in the message
> And for film from the 50s: that is most likely NITRATE, much more
----- here I agree with Richard Hess as to the phasing-out from 1952-55
Nitrate is not a stable material, it breaks down
> into nitric acid, &/or nitrogen gas!
----- cellulose nitrate need not be an unstable material, although it is -
because it is nitrated - very flammable. It is the process of manufacture,
where a mixture of sulphuric acid and nitric acid are working on the cotton
or other source of cellulose that may cause the instability. If the sulphuric
acid is not washed out properly, it will remain and start the decay, with
humidity accelerating it. Once the deterioration has broken some of the
nitrocellolose into releasing nitric acid, the process is autocatalytic and
heat-generating, i.e. accelerating. And that is the road to explosion.
>If someone were to drop a tin of
> deteriorated nitrate film in that storage situation, the result could be
> an explosion, instantaneous fire igniting the rest of the collection.
I have never heard about a shock as a cause for self-ignition.
> Thats not to say all nitrate film is bad- but it needs to be kept under
> carefully controlled and monitored conditions, and copied to a more
> stable base before deterioration sets in. Thats why the big
> repositories of film in the US have built literally underground bomb
> shelter type storage facilities.
----- the important thing in all nitrate vaults are vents to the atmosphere
via massive conduits - the explosion is thereby reduced to a fast and very
You probably know this: the first
> moving picture film is on nitrate and even though they stopped
> producing it when acetate was introduced, it was still around of course
> and filmmakers used it. Nitrate has a beautiful asthetic quality they
> felt they could not get in other types of film-of course its all black
> and white.
----- no, the reason for using nitrate film was much more mundane: it had
greater tensile strength and so could stand up to the wear and tear in at
times very old projectors on the circuit. Both the first di-acetate films and
the later tri-acetate films were worse in that respect. A sound film
attachment was just that: a piece of equipment that was installed in 1935 on
your projector from, say, 1915. And then, of course, the transparency is also
higher, giving better highlights. It is thought-provoking that in all
projection, all the light on the screen has had to pass through the small
film window - this is a tremendous power density on that small area. This
explains both why 16 mm was so quick to go to acetate - it was simply safer,
and why really lavish films use a 70 mm format. It is all going to be
electronic HiDef video/DVD in the future, of course.
Still photographic negatives have the same history but dont
> pose quite the threat because they are small and usually each is
> separated by its own enclosure.
----- unfortunately, it is frequently glassine envelopes, which damage by
acidic action of their own