Film-Tech Forum ARCHIVE: Cold storage (refrigeration/freezing) of films, vinegar, etc.?

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Posted by John Hawkinson (Member # 1135) on 09-18-2002, 11:45 PM:

I've got some questions on the proper way to make use of cold storage for films.

We recently got some refrigerators for the intent of storing test films, but there seems to be sufficient space to store some other films (old trailers, etc.), and I'm curious what the best solutions are.

Kodak's H-1 document, Preservation of Processed Film seems to essentially say "freezing and refrigeration are good, keep it below 36F, 15-30% RH."

Of course, I don't really have a good RH-controlled environment. Our current (breathing) storage cabinets live in the building's ambient environment, which is loosely temperature-controlled (and RH-controlled), but not really with an eye to film, so much as to people. And my refrigeration environment isn't RH-controlled either,
at least not very much, as far as I can tell.

The general recommendation for room-temperature storage is to not seal films in cans.

But Film Notes H-50-22 Test Film Tricks (on page 7) recommends storing in cans, and I recall explicit instructions with some test films to seal them in the can.

Am I correct in thinking that sealing test films in cans is the correct way to refrigerate them? At the moment, I get the feeling that the right approach is to place the film on a core, core in a plastic bag, bag in metal can, tape the metal can, and place it in a ZipLock (tm) bag. (The goal of the ZipLock bag is to maintain constant humidity inside the can, to avoid the instability of the RH in the fridge.)

Should I worry about effects from freezing, such that 33F is better than 28F? Or is freezing significantly advantageous?

Also, how does this deal with films that have already started to fade, and or get vinegarish (this is only an issue for some trailers)? Should I be concerned about vinegar syndrome continuing or worsening under freezing or refrigeration, or is it definitely going to be better than room-temperature?

Thanks for your recommendations/advice.

--jhawk

Posted by Leo Enticknap (Member # 534) on 09-19-2002, 02:09 AM:

As a general rule, I'd say that for nitrate and acetate, cool storage without any humidity control is a better bet than storage at room temperature. The underlying argument of this paper is that any temperature or humidity control is better than nothing. However, the condensers in domestic fridges tend to push RH up way above what it would be in the normal atmosphere, which has always made me a bit cagey about putting films in one.

The issue of whether to seal cans containing acetate elements or not is open to debate. My view would be that it should depend on the state of decomposition in each individual film. An acid detection strip will tell you this: in cellulose triacetate, pH 4 is considered the autocatalytic point. This means from this point on, a decomposing element will be generating enough acetic acid vapour to accelerate the rate of the reaction. Storing these in vented cans is crucial, but if you are storing both pre- and post-autocatalytic elements in the same vault, the pre-autocatalytic ones should be in sealed cans to avoid them being contaminated by offgases from the bad elements.

The widespread use of polyester film is so new that in truth, we don't really know what the long-term storage issues are yet. The last copy I have of the International Federation of Film Archives' storage guidelines does not even give any recommendations for temperature and RH for poly, though it is five years old. We have so little polyester motion picture film that reading up on this is not a priority for me at present. For magnetic tape the recommmendations are <16°C +/- 2%, and 35%RH +/- 5%. But the colour dye issues with polyester film are largely the same as those with 'fresh' acetate, so as low a temperature and RH as you can achieve is probably the way to go.

Posted by John Pytlak (Member # 331) on 09-19-2002, 08:06 AM:

JHawk: As Leo stated, most refrigerators have very poor control of relative humidity. So storing film in unsealed containers could subject it to excess humidity or even actual water/ice crystals.

Film can be preconditioned to a low humidity, then sealed in the container for refrigeration or freezing, as you propose to do.

The other option is to put Molecular Sieves with the film in the sealed container. The Molecular Sieves will adsorb excess moisture, and any acid vapors that may start to form. Don't overdo the amount of Molecular Sieves, or you could dessicate the film, causing curl, brittleness and shrinkage:
http://www.kodak.com/US/en/motion/support/technical/storage1.shtml
http://www.kodak.com/US/en/motion/support/technical/vinegar.shtml
http://www.kodak.com/US/en/motion/support/technical/molecular.shtml
http://www.fpchollywood.com/

I frankly don't see the need to refrigerate films that are in current use, and that you plan to replace as they wear out (e.g., test films). Cold storage will greatly reduce the rate of dye fading and vinegar syndrome, so refrigerating decades-old fading triacetate prints will help keep them in their present state without further deterioration.

------------------
John P. Pytlak, Senior Technical Specialist
Worldwide Technical Services, Entertainment Imaging
Research Labs, Building 69, Room 7525A
Rochester, New York, 14650-1922 USA
Tel: +1 585 477 5325 Cell: +1 585 781 4036 Fax: +1 585 722 7243
e-mail: john.pytlak@kodak.com
Web site: http://www.kodak.com/go/motion

Posted by John Hawkinson (Member # 1135) on 09-19-2002, 08:21 AM:

Thanks for the speedy replies, Leo and John.

At the moment I'm not terribly concerned with polyester. Most of our test films and old films of concern are on acetate. While some "future-proofing" for polyester might be in order, I'm not immensely concerned, and it's not as if I'm trying to run a professional archive here... [but that in mind, the datasheet for Kodak 2383 seems to have much the same recommendations]

John, you mention pre-treatment before sealing; could you elaborate on what sort of treatment should be done? As for mollecular sieve and dessicants, I was under the impression that they were to be used as a temporary measure only, and not for films that might see storage of more than, say, 6 months.

Incidently, on "is it worth it for test films?", we don't end up using test films more than a few times a year, and our budget for new ones is pretty small. We even have some dating back from 1979 or so. While I don't really expect that any test films bought recently will still be in use in 2025, it's enough to make me at least think about the issue.

Perhaps I need to explore the "How do I tell if this Cat69 or RP40 is too shrunk to use?" question...

--jhawk

Posted by Leo Enticknap (Member # 534) on 09-19-2002, 08:39 AM:

Well, if your RP40 has shrunk so much that perf damage is inflicted, with the result that the picture jumps up and down like a cat which has eaten a Vindaloo from one of Bradford's famous curry restaurants and then walked onto a bed of red hot coals, then it's had it (both the film and the cat)! As for a test film for analogue optical sound, I suppose that moderate shrinkage could significantly affect the frequency response, though I'm guessing here.

Posted by John Pytlak (Member # 331) on 09-19-2002, 09:09 AM:

Preconditioning would mean equilibrating the film to between 20 and 30 percent relative humidity, as specified in SMPTE Recommended Practice RP131. For small rolls of 35mm film, it may take several weeks to reach equilibrium with the lower humidity. Slowly winding through the film several times during the precondtioning should speed up the process by releasing any trapped moisture.

Molecular Sieves are intended for long-term storage applications, as outlined in the instructions:
http://www.kodak.com/US/en/motion/support/technical/molecular.shtml

I would question the use of any triacetate test film over a few years old, since even a few tenths of a percent shrinkage will affect any critical dimensional performance. I do not see a need to refrigerate any ESTAR base test films.