if you go to bed with a clay ingot mold raw in a fire when you wake up it turns into a ceramic ingot mold raw. Just a funny glitch
clay turning to ceramic when burned? never heard of something like this...
joke aside: it's more or less normal behavior as that is more or less exactly how you make ceramic stuff: you burn clay in fire over hours (and sleeping is a 6 hours fast forward), though if you don't do it right normally it shatters when you take it out.