Here's a fact sheet with some infomration on the use of copper  - which aprat from being used in all kinds of gadgets and technology, for examples in cars & computers, it  is often used in Buddhist ritual objects, such as rupas and singing bowls. This gives it immediately an added ethcial dimension - it seems difficult to wish to purchase a beautiful object designed to raise our level of consciousness and support our dharma practice, if it seems it potentially involves a lot of suffering and environmental destruction. It has certainly made me consider the use of stone or wood as materials for rupas. 

The fact sheet has been produced by Karen Luyckx from the Crydon Triratna Sangha UK