RE:Working with Metal Clay
Some metal clay pieces can be torch-fired, at least the fine silver variety can be if the piece is small enough. I haven't kept up-to-date on every type of clay, so I'm not sure about copper and bronze. Our sister pub, Art Jewelry, has a video on torch-firing. You can find it here:
http://art.jewelrymakingmagazines.com/en/How%20To/Metal%20Clay.aspx
Good luck!
Julia