Start with a mild cleaner and use stronger cleaners until you get the results you're after.
In addition to the Texaco lens I mentioned in my previous post I cleaned a badly oxidized 1 piece Gulf globe. The globe had a kind of iridescent glaze. It looked really bad. I tried several cleaners with no luck. I eventually tried Brasso and it removed most of the oxidation.
Wanted: Gas pump globes:Sinclair & affiliates, IL companies. Ripple bodies. Anything Sinclair, Stoll, Pierce, 4 Bros.
http://www.lastgas15.com/