How to clean painted pin back button?

[Fourman110]

Found a colorful pin back button (like political button), but it has crusty stuff stuck to it. I tried soaking it in water and gently rubbing it with a toothpick, which helped a lot. The stuff looks like it is on top of the paint not through the paint.

Any ideas on how to clean it? Would lemon juice hurt?

 

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[Normsel]

let it soak in soapy water and do a test spot or gently clean with a toothbrush

Dawn dish detergent is pretty good