7th
This is a sad sight - I tell my classes about the danger of firing too fast in the bisque (or the ware being too wet.) Telltale sign that this was a steam explosion is the almost gravel-like piles of pot rubble mixed in with the larger shards. There’s even a good chance here the small bits were a thicker, wetter piece nestled in the shattered bowls which may have survived if it weren’t for their explosive neighbor. More likely the bowls’ feet were a bit too thick or wet to take the temperature rise.
Work that’s ready for the bisque is called greenware; it’s bone-dry and when handled is NOT cool to the touch. A key to safe firing is to give the work plenty of time below the temp of 212ºF (boiling point) for any remaining moisture to evaporate out of the work. You can tell that this moisture is gone by holding a glass jar over one of the peepholes. If it steams up, there’s still remaining moisture.
Once past the boiling point, there’s still chemical water bound up in the molecules of the clay. The gaps left by the escape of the physical water leaves room for the chemical water and organic materials to burn out, a process that ranges well up into the 600º-700ºF range. Many potters handle these delicate transition periods by simply firing very slowly until they see color (dull red heat) in the kiln, which occurs above 900ºF.
from clamlab:
oops
(via pppots)
