Source: adafruit industries blog
Article note: Well that's cool and useful.
Looks like it's basically a displacement reaction with not-too-nasty supplies.
I wish there were text instructions, it _appears_ to be 10 mg Cupric Oxide (pretty sure it's CuO, it's black so it's not CuO2 or Cu2O) dissolved in hot 20ml 85% Formic Acid + 100mL distilled water that reduces on the surface.
In a follow-up to her recent video where she electroplated the gas tank of her motorcycle with copper, Laura Kampf decided to try a much easier method of simply painting on a copperplate solution.
She saw a video demonstrating the technique and wanted to try it out. It appears to work. Amazing. As she points out, this could lend itself to all sorts of applications.