[jan-jaap]

Those look like they could be cleaned up using a fiberglass pen (polishing to get to bright copper)

Excellent tip, thanks. This software guy is learning something new every day :-)

We happened to have one of these in the lab so I gave it a try. It's quite abrasive, I guess you don't want to overdo this. And as always when dealing with fiberglass you'll have itchy hands afterwards.

I'll do the rest at home, I have all the material there.