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

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

Articles	Variegating Glazes This is an overview of the various mechanisms you can employ to make glazes dance with color, crystals, highlights, speckles, rivulets, etc.
Glossary	Dolomite Matte Dolomite matte glazes have the potential to be very silky and pleasant to the touch, while at the same time being hard, durable and non-crazed (if they are formulated correctly).
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	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	Opacifier Glaze opacity refers to the degree to which it is opaque. There is more than meets to eye to the subject of opacity control.
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	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	Phase Separation Phase separation is a phenomenon that occurs in transparent ceramic glazes. Discontinuities in the internal glass matrix affect clarity and color.
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!
Oxides	MgO - Magnesium Oxide, Magnesia

By Tony Hansen