A frit is a glaze ingredient made by melting raw materials into glass, cooling it quickly and grinding it to powder. Fritting makes soluble or toxic materials stable and insoluble, and gives glazes a reliable melt.
What Is Frit?
Some useful glaze materials, such as borax and soda ash, dissolve in water, which makes glazes behave unpredictably in the bucket. Others can be hazardous to handle raw. Melting them with silica and other oxides into a glass, then grinding it, locks them into a stable form that mixes like any other powder.
Frits are especially important at low and mid temperatures, where they supply boron and other fluxes that help glazes melt smoothly. Many commercial cone 6 and earthenware glazes are built around one or two frits, and lead frits were once common in low-fire glazes, which is why lead-free frits are now the norm.
Each frit has a published chemistry, so glaze software can calculate how a recipe will behave. Frits from different makers aren’t always interchangeable, even when they have similar names, so substituting one means testing again on tiles. Keep frits dry and labelled, since many look identical.
This pottery glossary entry from Le Studio Art Space is general educational content. Always follow the clay, glaze and kiln makers’ data for your own materials and equipment.