Glaze Variegation Property

In contrast to the typical homogeneous surfaces of sanitaryware and most table ware, reactive glazes exhibit discontinuities in texture, matteness, reflectivity, color, etc that are called variegation. These variations are normally caused by crystallization, speckling and rivulets and opacity variations associated with phase separation. By understanding these mechanisms it is possible to produce glazes of more interesting appearance.

Mechanisms

Oxides	ZrO
Oxides	Li₂O
Oxides	CaO
Materials	Iron Oxide Red
Oxides	P₂O₅
Materials	Ilmenite
Materials	Rutile
Materials	Iron Pyrite
Materials	Granular Ilmenite
Materials	Granular Rutile
Materials	Tin Oxide
Materials	Titanium Dioxide
Oxides	TiO2

Variegation and phase separation with about 5% rutile

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The glaze is a dolomite matte fired to cone 10R. High fire reduction is among the best processes to exploit the variegating magic of rutile.

Links

Glossary	Phase Separation Phase separation is a phenomenon that occurs in transparent ceramic glazes. Discontinuities in the internal glass matrix affect clarity and color.
Glossary	Crystalline glazes A type of ceramic glaze made by potters. Giant multicolored crystals grown on a super gloss low alumina glaze by controlling multiple holds and soaks during cooling
Glossary	Crystallization Ceramic glazes form crystals on cooling if the chemistry is right and the rate of cool is slow enough to permit molecular movement to the preferred orientation.
Glossary	Opacifier Glaze opacity refers to the degree to which it is opaque. Opacifiers are powders added to transparent ceramic glazes to make them opaque.
Glossary	Reactive Glazes In ceramics, reactive glazes have variegated surfaces that are a product of more melt fluidity and the presence of opacifiers, crystallizers and phase changers.
Glossary	Reduction Firing A method of firing stoneware where the kiln air intakes and burners are set to restrict or eliminate oxygen in the kiln such that metallic oxides convert to their reduced metallic state.
Glossary	Magnesia Matte Magnesia matte ceramic glazes are “microstructure mattes” while calcia mattes are “crystal mattes”. They have a micro-wrinkle surface that forms from a high viscosity melt and microscopic phase separation, both of which prevent levelling on freezi
Glossary	Mechanism Identifying the mechanism of a ceramic glaze recipe is the key to moving adjusting it, fixing it, reverse engineering it, even avoiding it!
Glossary	Variegation Ceramic glaze variegation refers to its visual character. This is an overview of the various mechanisms to make glazes dance with color, crystals, highlights, speckles, rivulets, etc.
Oxides	MgO - Magnesium Oxide, Magnesia

By Tony Hansen
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