An improvement in an etching process in which the etched product, the surface of which is covered with a film of aqueous etching liquid containing ions of the material etched, is rinsed with an aqueous liquid and the resulting liquid, now containing said ions in dilute concentration, is passed through...http://www.google.com.au/patents/US4147581?utm_source=gb-gplus-sharePatent US4147581 - Etching of metal
