I clean my glasses with whiteboard cleaner, AKA Isopropyl Alcohol, largely because it's provided free at work. It works a treat. I've been toying with taking it home to try removing some stubborn chewing gum.
(Stevie) Yes, metallic lead is not a hazard. My mains water comes through several feet of lead pipe. I've just made a little counterweight for my trombone out of lead from an old car battery which involved melting it and bashing it into shape. It's worth not ingesting lead compunds though and the banning of tetraethyl lead from petrol was a good thing. I wouldnt't say it was joining the EU that has made us so risk-averse; they have just added an extra layer of absurdity to a process that started about 30 years ago in which we decided to become princesses, or as I prefer it, spoilt wankers. Acetone, BTW is one of the least toxic organic chemicals, comparable with ethanol, i.e you can drink it, preferably diluted.
(Phil, aka Stevie) IPA (chemists' term for isopropyl alcohol) won't shift chewing gum. That stuff is little better than an organic version of Blu-Tak, i.e. resistant to almost anything. Try a blowlamp. This post is from penelope, who has broadened her portfolio, as they say.
Bubblegum will often yield to a stint in the deep freeze. Oh, penelope already said that. To keep with the theme of chemical application: Try pouring a little liquid nitrogen on the bubblegum (and anything else your scientific interest in catastrophic failure under cryogenic shock lights upon - pens, fruit esp. grapes, and rubber gloves are classic favorites) and carefully prying it off. Use At Own Risk - not responsible for shattered glasses, pullovers, cricket bats, shoe-soles or whatever.