Scrub
What did you use to get the toner off the copper? I’ve used Scotchbrite pads and it takes me ages. Recently, I discovered trichloroethylene, which can be used to just wipe it off, but I don’t think it’s too kind to the environment.
Mmmmm… solvents…
I used acetone, in the rather mild form of nail polish remover, to get the toner off. It takes a bit of effort, too. I’ve been told of a solvent called “Ultrasolve”, which sounds good. Probably the kind of thing where the postman will deliver it wearing a chemical hazard suit! Where can you get trichloroetheylene (trike) nowadays? My dad used it as an engine degreaser back in the 1970s, but I thought it would be hard to get now.