> Or just scrub the board with a bit of ferric chloride and a sponge. If you use ink pen and transfer pads like I did decades ago, the sponge would almost cert

> Or just scrub the board with a bit of ferric chloride and a sponge. If you use ink pen and transfer pads like I did decades ago, the sponge would almost certainly wipe the pads off. The best way that I'm aware of to ensure the copper is being consistently covered by the solution is to use an air pump to produce bubbles under it. Those used in aquariums are quite cheap and durable.