I bought a crystal inkwell today, cleaned up the glass, polished it as best as I could. The problem is there are really OLD ink stains over the metal and these are not your usual water soluble modern fountain pen ink stains. I have this same problem on another I bought a few months ago, they are usable as inkwells, that is not my problem, they just don't look as visually appealing as they could do...
I tried ammonia and that does practically nothing... I don't want to damage the metal either, so what do I do?

Wonder if Brasso will work...

I tried that but its not brilliant, I will try again...
I don't mind some ink stain on these inkwells as it kind of adds to the history, but nothing I have tried really does anything to the stains at all. Brasso did remove certain little stains here and there but other than that the main bulk of it stayed there solid.

Have you tried solvents?

You might have to dip the inkwell because solvents evaporate very quickly.

Ultrasonic cleaning might work but only if the metal parts are easily detachable. You don't want to subject old glass to ultrasound.