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.
•The secret to cool bodies and glazes is a lot of testing.
•The secret to know what to test is material and chemistry knowledge.
•The secret to learning from testing is documentation.
•The place to test, do the chemistry and document is an account at https://insight-live.com
•The place to get the knowledge is https://digitalfire.com
- 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).
Out Bound Links
Crystals can form during cooling and solidification in many kinds of glazes and they can be microscopic or very large, widely scattered or completely covering. Matte glazes (e.g. high CaO) are often such because of a dense mesh of micro-crystals growing on the surface. Unwanted crystallization is ca...
Glass vs. Crystalline
In ceramic technology the term 'glass' is contrasted with the crystalline state, it is seen as a "super-cooled liquid". When crystalline materials solidify the molecules have opportunity to orient themselves in the preferred pattern during freezing whereas in a glass the random orientation of molecu...
When ceramic melts are cooled they prefer to solidify as an organized molecular structure. Given sufficient time and sympathetic chemistry, they will form a crystalline structure. But if cooling is faster they solidify as a glass.
Crystals can grow in cooling glaze melts if one or more of the fol...
The Awesome Crystalline Glaze Gallery of Tilton Pottery