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This is pure soda feldspar (Minspar 200) fired like a glaze at cone 4, 5, 6 and 7 on porcelainous stoneware tiles. The bottom samples are balls that have melted down at cone 7 and 8 (although they appear to be well melted they exhibit no movement in a melt fluidity test. Notice there is no melting at all at cone 4. Also, serious crazing is highlighted with ink on the cone 6 sample (it is also happening at cone 5 and 7). Feldspars have high KNaO, that means they have high thermal expansions. That is why high-feldspar glazes almost always craze. Since feldspar is barely melting at cone 6 it is not possible to make a functional cone 6 glaze that only uses feldspar as the flux (boron, lithia or zinc are also needed).
Glossary |
Feldspar Glazes
Feldspar is a natural mineral that, by itself, is the most similar to a high temperature stoneware glaze. Thus it is common to see alot of it in glaze recipes. Actually, too much. |
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Materials |
Minspar 200
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Materials |
Feldspar
In ceramics, feldspars are used in glazes and clay bodies. They vitrify stonewares and porcelains. They supply KNaO flux to glazes to help them melt. |
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