Why is my fired ware weak and brittle?

This is normally a very good indication that the ware is underfired. All fired clays develop increasing strength as the firing temperature increases up to their maturing point. Beyond the maturing point they will become weaker and begin to deform.

Porcelain clays also follow this trend up to a maximum value reached close to the top of the temperature range quoted for that particular clay. However, porcelain clays then very quickly lose strength as the firing temperature is increased, and also the glazes will begin to craze.

To resolve weak and brittle ware, increase your firing temperature to the recommended maturing point. It may help to check the kiln using pyrometric cones. For more information on firing temperatures follow the link to our Kiln Firings Programs guide.