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Is there a standard temperature and humidity recommendation for mixed collections? (10/27/06)

Our institution's collection is composed of diverse materials, including metals, wood, various organic materials, plastics, ivory, textiles, glass, and ceramics. Can you recommend specific temperature and humidity ranges for diverse collections like ours? We are aware that different types of materials require different environments, but is there a standard for mixed collections?

There are standards for common library materials such as paper, microfilm, CDs, video tape, and audio tape, but not for the diverse materials that you have listed. Only library and imaging materials have storage recommendations made by recognized standards organizations. For library materials, the organization is the National Information Standards Organization, or NISO, acting through the American National Standards Institute (ANSI). For imaging materials (including film, photographic prints, plates, optical discs, and magnetic tape), it’s the International Organization for Standardization, or ISO. There are no analogous standardizing bodies for objects conservation. As you mentioned, different materials have different temperature and relative humidity requirements. Cold storage benefits many materials, but a storage temperature that is too cold may damage materials like magnetic tape or acrylic paintings. The state of deterioration of the collection materials is another key factor in determining storage requirements. For example, acetate film in good condition should be kept cool or cold and moderately dry, but film that has begun to deteriorate must be stored under even colder and, to a degree, drier conditions. In short, it’s impossible to make a single recommendation for a general collection of unspecified materials. Even within a narrower range of collection materials, storage needs vary. The IPI Media Storage Quick Reference, which deals only with imaging media (optical discs, magnetic tape, photographic prints and films, etc.), tells us that the preservation of mixed collections depends on our understanding of the vulnerabilities and current condition of each material.

What's the correct warm-up time for materials coming out of cold storage? (7/20/06)

Our institution keeps motion-picture film in a cold vault set at 35°F, 30% RH. We have a staging area where films removed from storage are allowed to warm up before they are taken into the viewing/work area. Using your DewPoint Calculator I was able to determine a suitable set point for the staging area that is appropriate for the material and that avoids crossing the dew point, but I'm stuck on how long the material should remain in the staging area. Do you have any recommendations?

Many institutions are using the 24-hour, or overnight, warm-up rule. The approach is effective, safe, and easy to follow. The key to avoiding condensation is thermal equilibration. Data developed at IPI indicate that a single 35mm 1000-foot film roll will achieve 90% thermal equilibration after 3.5 hours. A stack of six 35mm 1000-foot rolls will achieve 90% thermal equilibration after 7.5 hours. Clearly, the material's mass is a factor; the more material you have, the slower thermal equilibration will be. So, while thermal equilibration isn't likely to take as long as 24 hours, the 24-hour rule works well in most situations. IPI has published data on both temperature and moisture equilibration rates for photographic materials. View report.

Stockpiling silver gelatin paper and film in the freezer (6/27/06)

With many companies leaving the silver gelatin paper and film business, is it wise to buy up and stockpile these materials in a freezer? Is fogging a concern? Is there a danger of ice crystal formation?

Freezing is the thing to do; it will greatly reduce the tendency of black-and-white materials to fog over time and will vastly improve their storage life. This is why the high-end photo supply stores kept their film and papers in the refrigerator. Fogging caused by radiation can still be a problem, but it’s not that common. The staff in one archives used to have to move everything out of the freezer before they did any X-ray examinations, because the X-ray equipment and the freezer were in the same room. In another instance, a photographic supply store had a troublesome fogging problem that turned out to be caused by the building itself: it was discovered that the building had been used for painting radium instrument panel dials for airplanes during World War II. The luminous paint (containing radium) had soaked into the walls and floor of the building (and, of course, it didn’t show up with the lights on). The store had to move to a different building. Kodak studies have shown that, given the water content of the materials during packaging, there should be no problem with frost or ice crystals forming if materials are frozen in their original packaging. Furthermore, thermodynamics shows us that the equilibrium between the condensed phase water in the film or paper and the vapor phase will shift towards the condensed phase; in other words, when a sealed package is frozen, the RH inside the package will decrease, and the water content of the film or paper in the package will increase. This condensed phase is not liquid water, although liquid water is an example of a condensed phase for water. Roll film in the little plastic cans should be fine to put in the freezer as they are, but, unless your photographic paper is still sealed in its original black plastic bag, it would be a good idea to double-bag it in zippered polyethylene bags before freezing, to keep the sheets from sticking together. The equilibrium moisture content in the freezer could be fairly high, so during warm-up the emulsion on the paper could get a little sticky. Double-bagging prevents the paper from adsorbing any more water vapor when the paper is frozen and will therefore more or less fix the water content.