Etching solutions are used to etch metals, concrete, and other materials. The type of etching solution you need depends on the material you're working wit
When used for PCB (Photoresis Circuit Board) etching, hydrogen peroxide is typically combined with hydrochloric acid (HCl) to create an effective etching solution, where the hydrogen peroxide acts as an oxidizer, allowing the acid to more readily etch away the copper on the board; the common ratio is roughly 2 parts hydrogen peroxide to 1 part hydrochloric acid.