I'm going to have fun at some point in the next couple of days, trying out something I've never done before: making up a Bordeaux Etch solution of equal parts copper sulphate and salt in distilled water in order to try etching aluminium plates. I've been looking on the web for information about how to make up the solution as my printmaking books are a bit vague. Both the Warringah Printmakers website and the reference to Cedric Green in the right hand side bar will give you a clue, if you want to do it. I was unable to find a chemist or a vet to supply the chemicals (apparently a copper sulphate mixture can be used on pets to treat wounds), but it was readily available at a local farm supplies store at only $7 per kilo. I'll let you know how I get on!
Willis tells me that the bite on aluminium is fast and unpredictable, but as I quite like foul biting and open biting perhaps that will suit me.