Crystal glazes are normally evaluated on the recipe level, people simply have a recipe that they know works and add colors to it. However there is a great benefit to knowing why crystals grow the way they do and what explains the variations in size, shape, color, etc.- Small zinc silicate crystals can be used to control where crystals grow in crystalline glazes.
- TiO2 dissolves into the melt during firing but normally re-crystallizes (or acts as a crystallization catalyst) during cooling (with rutile structure).
- Since Alumina stiffens the glaze melt, it will prevent the growth of crystals during cooling because it is more difficult for the specific oxides needed to form the crystal, to travel to the site of formation. Thus most highly crystalline glazes have very little alumina.
Oxides - ZnOAlmost all crystalline glazes are high in ZnO, its presence coupled with low alumina and adequate SiO2 is the secret. The very fluid melt created is perfect for growing a wide range of metallic zinc-silicate crystals.
- This glaze produces acicular crystals on a matte surface with a lovely and very touchable texture which, when glaze is applied thickly, tends to sparkle.
Oxides - TiO2TiO2 is used to control the way crystals grow in classic crsytalline glazes.
- Ilmenite seeds crystals in titania glazes.
- This glaze produces both zinc silicate and rutile crystals. Zinc silcate crystals are patchy, but rutile crystals occur evenly spaced throughout the glaze surface (though they may be more visible where glaze is very thick).
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