There are a bunch of ways to etch copper off boards, including the messy old standby etchant ferric chloride, or even [Sebastian]’s preferred sodium persulfate method. Being out of that etchant ...

[Arvid] is using the traditional method of etching away copper, just some ferric chloride and a bit of time. How he’s masking the copper that shouldn’t be etched away is a unique process we ...