No more calls; we have our winner.

Glasses frame is usually made of a type of copper called monel. Monel is a table metal and unreactive towards a lot of chemical. It is also skin friendly. The only downside is that it turns greenish when it gets rusty.

[edit] It’s interesting that that article suggests a way to clean them–but the Costco optician just now said you can’t really clean them. (They replaced them for no charge.)