Leadless High Borax/calcia for glaze. This is a USA pottery frit. Like Frit 3124, this can be a complete cone 06-02 leadless glaze with the addition of a little kaolin to suspend. Adding more kaolin and silica will produce glazes suitable for higher temperatures. Substitute in some Frit 4110 if glazes shiver or 3249 if they craze.
If used in too high a percentage, this frit can push the boron too high for use in underglaze colours.
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.
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.