I am going to start smithing steel and iron but I just wanted to know what should the crucible be made of. 
For smelting iron and steel you really need a high temp graphite, or cast able refractory of some good thickness. You want a good thickness of material that is rated at 2400-2500 some clay companies sell refractory clay then you want what is rated cone 12, and you will need to fire it in a kiln…