While it’s possible to just buy (or make) a cupric chloride solution by treating scrap copper with hydrochloric acid, it’s easier to just throw all the ingredients together with the PCB to be ...

I've decided to make dancing flames. It's done by burning a mixture of aluminum, copper sulfate and hydrochloric acid.

It’s not like etching with hydrochloric acid and peroxide is anything new ... There are a bunch of ways to etch copper off boards, including the messy old standby etchant ferric chloride ...