So, maybe 2 years ago I bought a cool little ashtray at a flea market. It is a retro glass piece from a local (where we lived in WV) glass factory, Blenko.
After using it for a while and abusing it some, a nasty ash "film" covered the bottom and many hard-to-reach areas. Ash got rained on, then baked in by the sun. You can see here:
After multiple attempts at cleaning with dish soap, soaking, Brillo pads... nothing was getting this stuff off. Not a huge deal, but I really like this ashtray and of course they haven't made them in 40 or so years. I really wanted to clean it back up. Ah ha! Plain old white vinegar... Dissolved that crap right away and I scrubbed it one last time. Good as new.
I don't know if anyone has had a similar problem (or cares about their ashtray), but I wanted to share. Maybe kind of a "duh" thing as vinegar is a great cleaner and ash is a basic ph (right?) but I hadn't thought of it until today. Don't know if metal or ceramic ashtrays can get as grody as mine or if they are a little tougher.