|Monthly Tech-Tip |
This was made by a potter who carefully designed his own body and glaze recipe and obtained a high quality kiln in which to fire a line this line of ware. These pieces are being used in a restaurant and this one has failed. Why? It could be pushing up against the limits of this type of clay body (even at its best). Compared to what typical restaurant ware is made from it has more porosity (demonstrated by the color change around the crack). It likely has entrapped carbon inside. It has lower strength (a big issue restaurant ware which is handled so much). Larger particles of high expansion minerals create vulnerability to sudden temperature changes. If this is all true then all of the bowls will eventually crack.
That being said, what if they do not all crack? Maybe this crack appeared to relieve stresses within the ware from uneven drying or uneven firing (due to technique or uneven thickness). Some bodies expand upon absorbing water, if that is the case with this then the bare clay surfaces (which permit water entry) could be an issue also.
A method of firing stoneware where the kiln air intakes and burners are set to restrict or eliminate oxygen in the kiln such that metallic oxides convert to their reduced metallic state.