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Ok,the other day I was cleaning my tuba with some silver cream when I noticed that there is a kinda dark gray area on the bottom bow, I know its not tarnished or any thing like that, but it will not come off, every thing I have tried has failed horrible. Any suggestions?

I play on a HB2-CC with a silver finish, if thats important all.

Is it near the place where two parts join? It could be a solder stain--basically lead alloying wtih the silver in the plating. It's not harmful, just sloppy work.

Thousands of dollars in an instrument. Still, a work of art. Tubas are priceless.