Hello, I am new at engraving and doing simple engravings on coins and have tried black enamel paint for highlighting the engraving, but it won't stay in and will even wash out once it dries. Is there anything special I need to do to keep it in the engraved area or need to use something other than black enamel paint? Also how do I seal the coin to keep the black highlight from being worn out by touching? I read somewhere online that the coins can be sealed to prevent this. Thank-you for all your help.