Your better off using Rottenstone instead. Potash might be a little too coarse. That is once you have removed the clear sealer most have on them after final factory polishing. If the clear coat isn't removed, you can polish and clean till blue in the face with little accomplishment.
I remove it fairly easy using Easy-Off Oven Cleaner. The fume free in the blue can only (not harsh on my hands). I spray it all over the brass item, then place the item in a plastic bag . Let it sit for about an hour, depending on how tarnished they are. Afterward I just rub off,rinse well, then polish using Wright's Brass Polish. Use the rottonstone on items where a high gloss polished finish is wanted.
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