The plastics

The three suitable plastics

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The statement Which maps onto the catalog exactly So the shelf is almost entirely suitable material Uncoated is doing work in that sentence Which is an argument against decoration Glass is inert and heavy The standard behind the advice Ask the question anyway References

PET is polyester. That one fact decides most of this shelf.

The statement

"Suitable plastic enclosures are made of uncoated polyester, polyethylene, and polypropylene." Three materials, named, in preservation guidance from the Library of Congress.

Which maps onto the catalog exactly

PET is polyethylene terephthalate, which is a polyester. PP is polypropylene. HDPE and LDPE are polyethylene. Those are the materials this catalog is mostly made of.

So the shelf is almost entirely suitable material

81 PET and 64 PP out of 146 containers, plus one glass. By material, this is a conservation-appropriate shelf without anybody having curated it for that, because the catalog simply does not deal in the problem plastics.

Uncoated is doing work in that sentence

A coating, a print layer or an adhesive can be a different material from the container, and it is the part in contact with nothing you can see. For an enclosure the guidance wants the plastic itself, unadulterated.

Which is an argument against decoration

A printed or sleeved jar introduces materials the guidance has nothing to say about. For an archival use a plain container and a label on the outside is the conservative choice.

Glass is inert and heavy

One glass container on this shelf. Glass is chemically indifferent to everything a collection contains, which makes it ideal and breakable. For a display piece it is excellent; for a box of jars in a loft it is not.

The standard behind the advice

ISO 18902 and the Photographic Activity Test are what "photo-safe" means. They are tests on enclosure materials rather than on jars, and they are the vocabulary to use when asking a supplier whether something has been assessed.

Ask the question anyway

A container being PET does not mean it has been PAT tested. The material being a suitable one and the specific product having been assessed are two different claims, and only one of them is on a spec sheet.

References

Library of Congress, Care, Handling and Storage of Photographs: "Suitable plastic enclosures are made of uncoated polyester, polyethylene, and polypropylene." On standards: "To be considered photo-safe, storage materials must pass the physical and chemical requirements outlined in ISO 18902 including passing the Photographic Activity Test (PAT)." And on humidity: "Photographic emulsions may stick to plastic enclosures if they are exposed to high RH, especially above 70% RH." loc.gov

The Davis Pack Supply catalog, measured 18 October 2026. The numismatic and philatelic shelf is 391 rows: 146 containers and 245 closures. 81 PET, 64 PP and 1 glass, from 6 to 250 mL with a median of 118. Zero PVC. By colour 39 white, 35 clear, 23 black, 15 amber, 15 natural and 8 blue. Necks 70-400 at 113, 89-400 at 93 and 58-400 at 66.

Written from Library of Congress and NARA preservation guidance and from National Park Service Conserve O Gram material, and from the catalog as it stood on 18 October 2026. Conservation advice for a specific object is a job for a conservator; nothing here is a substitute for one, and a valuable or unusual item deserves that conversation rather than a jar.