To summarize, a fiber kiln with embedded elements is the best choice for firing silver clay. They can be used to fire bronze or copper clays, but doing so will significantly reduce the number of firings before the elements (and, therefore, the muffle in which they are embedded) need to be replaced. A firebrick kiln is the best choice for firing metal clays that require long firing cycles. Firebrick kilns can be used to fire silver clay, but the total firing time will be significantly longer vs. fiber kilns because of the slower heating and cooling rates. The best choice for you will depend on the type of metal clay you use most often.
John Hohenshelt began working summers at Paragon Industries at 13 years old. He performed almost every job in the production facility from operating machinery, welding, crating, to stacking kilns. After attending university (B.A. in Mathematical Economics and M.A. in Political Science, Juris Doctor.) He spent three years as a Captain in the U.S. Army. In 1998, he returned to Paragon Industries to work as a plant manager and learned electrical engineering and product design from his father. In 2001, he was named President of Paragon Industries. http://www.paragonweb.com
Article reprinted from Metal Clay Artist Magazine Vol. 1 Issue #4.