can anybody explain why some red clays will fire to stoneware temperatures? obviously, the presence of red iron oxide is going to bring the vitrification point down so what is it that allows some red clays to be fired to temperatures used in, say, ash glazing as used by, amongst others, Bernard Leach and Phil Rogers (at least the clay appears to be red). I've also found red clays used in glaze recipes that fire up to cone 9 and possibly beyond.
RED CLAYS
Aug 18, 2003
1 Replies
The vitrication point of clays in determined largely by the total amount of fluxes. Iron oxide does act as a flux, though much more so in a reduction atmosphere than in oxidation. Clays like Redart (see the analysis below) contain a fair amount of other fluxs.
% 0.38 Na2O 4.15 K2O 1.59 MgO 0.26 CaO 15.51 Al2O3 64.95 SiO2
1.09 TiO2 7.05 Fe2O3 0.22 P2O5 4.80 LOIIf you could removed the Na, K, Mg, and Ca, the vitrification point would be much higher. So, it's certainly possible to have a red clay that fires to cone 10 - BUT you probably will need to avoid a reduction atmosphere.
deg
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