... saving ,Environmental protection . etc Graphite crucible have four different main type .Item 1 , Pure graphite crucible . The carbon content always > 99% . ... 200-250 times )Item 2 Clay graphite crucible The cheapest and the lowest qualiy . the life is always 1/20 to 1/15 ... , gold ,silver, zinc, aluminium , lead , cast iron .etcAnd we have the special crucibles used in melting pure cast iron which need ...