Petalite

Priced per pound. Quantity discounts are available.

Petalite (LiAlSi₄O₁₀), also known as castorite, is a lithium feldspar with a high silica content. It is used both in clay bodies and glazes to help decrease thermal shock problems. If used in large quantities it can cause glaze fit problems.

Petalite is unique for its thermal properties; like many lithium-bearing compounds, it has a very low rate of thermal expansion, making it a valuable addition for cookware-intended claybodies (such as flameware). Petalite actually has close to 0% thermal expansion, which makes it one of the best addititives for this purpose. This low thermal expansion may affect glaze fit, however -- because most glazes do tend to expand and contract (regardless of lithium content), when they are placed on a Petalite-bearing claybody, crazing will likely result as the claybody won't move much and the glaze will.

In glazes, Petalite tends to create silky white surfaces at high and low temperatures and in both oxidation and reduction atmospheres. Because it has such a low iron content, it is a popular glaze additive for white and clear glazes, as it melts without delivering a noticeable tint.