SPOD
A lithium mineral that carries its alumina and silica with it · Lithium is a powerful flux, and the lowest-expansion of the alkalis · Barely dissolves, so it stays put in a stored glaze · A heavy substitution can drop expansion far enough to shiver a glaze
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Spodumene is a lithium mineral that carries its alumina and silica with it, so it goes into a recipe as a glass-former rather than as a bare flux. It barely dissolves in water, and it gives off almost no gas.
Spodumene brings lithium into a glaze or a body already combined with alumina and silica, which means it can carry a large share of a recipe rather than being dosed in at a few parts in a hundred. Lithium is a powerful flux and it lowers thermal expansion further than the other alkalis do, so a glaze taking a lot of spodumene can end up fitting very differently from the one it replaced — far enough, if the swap is heavy, to shiver off a sharp edge. It barely dissolves, so a stored glaze keeps its lithium where it was put, and almost none of its weight leaves as gas during the firing.
