Post's 244 - a fat magnesium white at cone 6
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The tiles above are part of a 244 glaze line blend. The glaze on the farthest left has 1.0 gram of copper carbonate in it. The tiles next to it descend in copper 1/10 of a gram at a time. So the range of this line blend is from 1.0 grams of copper carbonate on the far left tile to 0.6 grams of copper carbonate on the glaze that is to the far right. Click the image to enlarge the tiles.
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This glaze got its name because it has 2 moles of KNaO, 4 moles of MgO and 4 moles of Cao. For those who aren't up on their chemistry that means that this glaze has significant amounts of both magnesium and calcium carbonate as the main fluxes (melters). My goal when I created this glaze was to make a fat magnesium white that would fire at cone 6.
The tile on the left is Post's 244 base glaze. The tile on the right has 3% tin oxide added to it.
I also tried dabbing Duncan, Sax and Amaco lowfire glazes (cone 06) and underglazes onto Post's 244 with a circular sponge and firing them to cone 6.
As you can tell from the test tiles the low fire glazes didn't run at all even though they were fired to 2200°F, about 300° hotter than the cone 06 they are rated for.
