Plainsman Clays | NESY
Nepheline Syenite
Nepheline syenite is a finely ground alkali rock that melts at a lower temperature than feldspar. It is the raw flux most cone 6 glazes are built on.
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Nepheline syenite is nepheline with feldspars alongside it and no free quartz at all. Compared with a feldspar it contains more alkali, more alumina and less silica, so it melts earlier. Roughly a quarter more feldspar would be needed to do the same fluxing. It is not a straight swap for feldspar, though. Trading feldspar for it takes silica out of the recipe, and that silica has to be added back somewhere. The extra alkali also raises thermal expansion more than a feldspar would, so a glaze that relies on it heavily can craze unless something else in the recipe pulls the other way. The finer grind melts more readily than the coarse.
- A finely ground alkali rock, nepheline with feldspars and no free quartz
- Melts earlier than a feldspar, with more alkali and alumina and less silica
- A common flux in mid-range bodies and glazes
- Raises thermal expansion, so a glaze built heavily on it can craze
