Re: Armatures in clay
All good advice, but I offer another angle.
I've made several hundred life size heads in ceramic and this method has never resulted in explosions, breaks, and hardly even any hairline surface cracks. I use a simple pipe with a big wad of newspaper at the top as the armature and build the clay up around that, then slide the head straight up, off the pipe. let it dry and let the paper burn out in the kiln. Some walls have been over 6 inches thick. The catch is, the clay must contain grog, it must be steam dried instead of air dried, and it must be fired low and slow.
Small figures, I use the clay itself as an armature (hardened) and fire them solid.