F3134

Frit 3134 is a calcium borosilicate frit with no alumina in it and a great deal of boron. It melts low and runs, and it suits a recipe already carrying enough clay to supply the alumina itself.

Frit 3134 brings no alumina of its own, so in a recipe built on it the alumina comes from the clay instead, which lets the recipe carry more clay — and clay is what keeps a glaze in suspension. The boron makes it a strong melter at low temperatures and a common answer where a recipe called for Gerstley borate; it flows around 870°C. It is not a low-expansion frit, whatever the boron suggests: there is enough calcium and soda in it to outweigh what the boron does, so a glaze that fitted before can craze once this goes in. Boron also dissolves slowly out into the glaze water, so a standing bucket loses flux.