[freosam]

True. Although the ziploc bags can just be left a bit open, that's quite sufficient. The good thing about food-safe bags is that they're usually polypropylene and so good for archival use (and much cheaper than anything from a preservation-supplies shop).

[ninalanyon]

> food-safe bags is that they're usually polypropylene

Interesting.

I've just checked the biggest grocery site in Norway (oda.com) and two out of the three bags they sell were low density polythene, the third was polypropylene.

Not a big sample I'll admit. I'm pretty sure that the very thin bags provided in supermarkets here for fresh loose produce are also polythene.

[freosam]

Oh right, I've never seen polythene resealable ones here in Australia. (The floppier 'freezer bags' are I think, but they're less useful for archiving.)

I think it's mainly PVC that's to be avoided for archiving, and office supply shops are full of the stuff (document sleeves, etc.).

An archivist once told me that if you burn a bit of plastic and it doesn't give off any smoke then it's likely polypropylene or similar, and so good to use. That's never felt like a particularly robust test though (but I'm not a chemist).