Hi guys, after I'm done etching, using PnP (Press n Peel) paper
and Ferric Chloride, there's this black stuff left on the copper
and I can't seem to get it off.
If it's the resist itself, use a chemical remover. I think it's
lacquer thinner, but methyl ethyl ketone will definitely do it; or
you can mechanically remove it by polishing. Usually, I just use a
foam bar made for acrylic fingernails. A fine or superfine (about
400-600 grit) bar leaves a satin finish that is easily polished out.
If it's the smut residue left in the etched areas, just pop it in
the Sparex or peroxide pickle for a few, or brass brush it. It does
need to be removed, as it will affect any patina.