I was cruising through the various pottery groups I belong to on FB, and there was this piece about really thick items:
[Dick White])
Even it is completely dry at 212⁰F and doesn’t explode, there is a second period of chemical water formation at around 900⁰F as the clay molecule reorganizes into the ceramic silica and alumina oxides. That will cause a piece that is too thick to crumble into large shards (though not explosive, just a pile of rubble). Don’t do it. If the sculptor doesn’t know his or her materials, you shouldn’t accept the risk of their ignorance.