Some powders  have copper erasures, like tin oxide.
https://www.thehighroad.org/index.php?threads/list-the-copper-reducing-powders-please.823522/
Clean the bronze brush in Isopropyl alcohol . 91% less water.
				
			https://www.thehighroad.org/index.php?threads/list-the-copper-reducing-powders-please.823522/
Clean the bronze brush in Isopropyl alcohol . 91% less water.
			
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