Aluminum Etch

etching solution used to etch aluminum. Typically aluminum etches are based on phosphoric acid. A common aluminum etch formula would be phosphoric acid, H3PO4, 80ml, nitric acid, HNO3, 5ml, and water, H2O, 15ml  acetic acid, CH3COOH, will sometimes be added as a buffer. Aluminum etches evolve hydrogen bubbles that may cling to the aluminum layer being etched locally preventing etching, and leaving behind aluminum residue, "snow". Some mechanism such as agitation or low pressure must be supplied to remove hydrogen bubbles. Surfactants may also be used to enhance  wetting.