Zero3 H High Expansion Variant
Recipe
Notes
This is a high-expansion version of the Zero3 Clear glaze (code G2931K), originally developed from the Worthington Clear Gerstley Borate based recipe. While G2931K fits the vitreous Zero3 porcelain and stoneware and also non-vitreous low-talc bodies (like Plainsman L212, L215), it shivers on high-talc bodies (e.g. Plainsman L213). That means that this G2931K variant is the most similar to commercial low fire glazes (which are designed to fit high-talc bodies). This version increases the thermal expansion of Zero3 K glaze from 7.4 to 8.0 (by adding increasing KNaO at the expense of MgO, ZnO). Do not try to use this with too little water. Mix it to 1.43 specific gravity and add vinegar or Epsom salts to gel it so that it stops moving (after vigorous stirring) in 2 or 3 seconds. When mixed right it applies very well to low or high porosity bisque (in a very thin layer if needed), it does not drip or move. The hold:slow-drop firing schedule, like 04DSDH, is critical to a defect-free surface.
Description
A cone 03-02 higher expansion fritted clear glaze developed from Worthington Clear.