How can I make my pieces frostproof?

Pottery is damaged when moisture that has been absorbed into the clay, freezes. Water expands as it freezes and the force of this expansion can cause a pot to crack or the surface to shale off.  It is almost impossible to make a pot totally frost-proof because all clays have some porosity. Low-fired terracotta clays will readily absorb moisture but this can also happen, to a lesser extent, to high fired stoneware and porcelain clays too.

The best defence against frost damage is to use higher firing clays and to use glaze which, if correctly applied will reduce moisture absorption. Clays with higher grog content will have greater strength to resist damage.