u/chair-1972

I am engraving some Brass Plates with a diamond tipped drag engraver, the engraving itself looks good, but to make it more readable I use brass black to tarnish the engraved pockets, I used no a bit of nailpolish on the surface applied before the engraving to mask the restof the plate, but a bit of the brass black still gets through from time to time, how can I get that of without also removing the tarnish in the engraving. The picture isnt great its more to illustrate how the finished product should look