nitrocellulose is somewhat soluble in isopropyl alcohol.  Common stuff,
over here (think NC laquer rather than gunpowder.  Or "nail polish")

Another possibility is some of the micro-fine powdered polyethylene (again,
used in the cosmetic industry.)  I probably wouldn't work quite by itself,
by you could probably put it in a water/alcohol carrier and then bake it
on to fuse it to the copper.  (rather similar to laser printer toner in that
respect.)   For that matter, I wonder what's in those opaque-ink "gel" pens
that are appearing all over (these have a light-colored base that works on
black paper, but they're fluid enough to work in more-or-less standard
ballpoint mechanisms...)

BillW

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