Aluminum, unfortunately, is not a good metal to use. The melt point is extremely low and it has very strange characteristics. Brass, bronze, copper, silver, gold, platinum, and some other non ferrous metals are o.k. Nickel can cause allergic reaction to about 20% of the population so that is not recommended but can be done. It is a hard metal as well requiring a lot of force. There are quite a few metals that can be considered toxic, like lead. Aluminum as well in fact.