any kind of solvent will work wonders .. i was , well am a printer, and i would take my pieces into work and soak them with all kinds of good stuff like isopropyl alcohol. methyl ethyl ketone, normal proply actetate, ethal ecetate, denatured alcohol, butyl acetate, etc.. any of these things will do wonders on your glass products.. just make sure to wash them out well with some plain tap water when you're done with any heave chemicals like the ones i mentioned..
i've tried the salt thing before, but tbh, i don't think it does much so now i prefer to safe it for my popcorn..