COST
A dry blend of feldspar, quartz and kaolin · Secondary flux for glazes, clay bodies and engobes · Melts higher than feldspar, not lower — not a one-for-one swap · Gradual melt and lower surface tension through cone 6 to 9 · Helps a slip bond to the body in engobes · Low in iron, fires white
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Cornish stone substitute blends feldspar, quartz and kaolin into a secondary flux for glazes, clay bodies and engobes. It melts higher than feldspar, so it is not a one-for-one swap.
Cornish stone substitute blends feldspar, quartz and kaolin. In a glaze it acts as a secondary flux and a feldspar alternative, but it is not a one-for-one swap for feldspar. It carries more silica and less flux, so it melts at a higher temperature rather than a lower one, and a recipe that trades feldspar for it straight across comes out stiffer — a glossy surface can move toward satin or matte. What it brings instead is a gradual melt and lower surface tension through cone 6 to 9, which is why it holds its place in recipes that crawl or craze. In an engobe it helps the slip bond to the body, and in a clay body it supplies fluxing oxides and fired strength. It is low in iron and fires white.
