Crystalline Glazed Pottery
The crystals formed in these glazes depend on the chemical composition of the glaze and the style of firing. Firstly the glaze must contain a lot of zinc and the catalyst to start the crystal growth. This is normally titanium. Then during the firing the glass being formed must be soft and runny to allow the growth of the petals within a reasonable time. The consequence for the potter is that the glazes are very mobile, tending to slip off the pot all over the kiln. They must be fired in oxidation to hold the zinc and cooled very slowly (holding the kiln above 1100 degrees C for an extra 3 hours). Once again the results are anything but predictable. The crystals are thought to be zinc silicate (willemite).
.JPG "Reduced copper red and oxidised crystal bowl, 22cm")
.JPG "Small rectangle with landscape crystal image, 23cm*16cm")
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