A frit is a type of ceramic glass. It is a combination of materials that, when melted together, are rendered insoluble and resistant to acid attack. They are, therefore, a means of introducing certain materials into a glaze which would otherwise be toxic. Frits can be used alone as low temperature glazes, e.g. raku and majolica, but generally they form the basis of a glaze recipe. Walker Ceramics offers a large range of frits and for those wishing to incorporate the frits in glaze calculations, molecular formulae are listed.
Lead Frits Glazes based on lead frits produce a shiny, durable finish and give brightness and clarity of colour when used in conjunction with oxides, stains, slips etc. While they can be used on all earthenware clays, they are particularly suitable for red clay.
Borax Frits Borax frits are often used in the production of earthenware glazes when a lead free glaze is required. Slight milkiness, especially at lower temperatures, may be evident over red clays, and the colour response with oxides, etc. is not usually so vivid as with lead frits.
Alkaline Frits Similar to borax frits, alkaline frits are noted for their high soda and potash content. The colour response from copper and manganese is turquoise and purple/brown respectively – typical of this type of frit. Alkaline frits have a high expansion rate which makes them a suitable base for crackle glazes.

The table below lists a detailed summary of the properties of the most commonly used frits.