I up-cycled a glass liquor bottle into a drinking glass (by means of scoring, heat-shocking, and polishing). What I'm left with is a lovely glass with some very stubborn label glue on it. How can I get rid of the glue? Big bonus points for something that doesn't involve nasty chemicals.
A car or household lubricating oil, such as WD-40 or 3-in-One oil (both are brand names in the UK) will dissolve the label glue. Put one or two drops on the glue residue and rub with, say, a paper towel for a few seconds, and the glue should start to come off.
I haven't tried using vegetable oils, so I don't know if any of those will work.
The best solvent I have ever found for stubborn materials is (surprisingly) "NZ tea tree oil".
It also does not seem to harm most surfaces - a paradox.
It's not known to be especially poisonous - it is sold as a health product.
The genuineness of the health claims made for it are unknown to me, but it seems close to the ideal solvent to have on hand.
Many sellers here - be sure it is from NZ tea tree (really). It's never cheap, but as a solvent a tiny amount is enough for most purposes, when all else fails. And, the result smells good :-). One seller here as an example - good website name :-} ie http://teatreeoil.co.nz/.
This is not the same as Australian tea-tree oil, which is derived from a quite different plant and is nowhere near as good as a solvent - sadly so as it is much cheaper. .
Eucalyptus oil is extremely good. Similar overall to NZ tea-tree oil. Not as good as a solvent but better than most. Inhale fumes for blocked chest. Put a drop on a spoon of sugar for internal use. May or may not work BUT those were among my (long ago) childhood remedies.
Ethyl alcohol, or meths (in NZ it no longer contains added Methyl alcohol despite the name). Not as good as above but often useful. Safe enough in small quantities (do not drive and label dissolve :-) ).
Acetone often does well. Likes dissolving some plastics.
Methanol (wood alcohol) is often effective. Nasty stuff and very poisonous - but the drop or so usually needed as a solvent should be easy to use safely.
Carbon tetrachloride was the mainstay of drycleaners for many years. A carinogen, absorbed through the skin and a liver poison. Charming. Still has its place if used sparingly in small volumes with great care.
Methyl Chloride !!!!!!!!!!!!!!!!!! Nasty poisonous stuff. Dissolves some things really well. Will chew apart set epoxy (with violent cracking). Has its place. Use with extreme care.
I just realized that direct heating with a flame does a pretty good job. Boiling water wasn't enough, but heating with a flame seems to do the trick. After heating, wiping with a rag takes the glue off.
There is still the smallest amount of residue left after the flame-and-wipe. I'll give @Claran's oil suggestion a try and compare the results.