While titanium dioxide is used in glazes as an opacifier, it is not as effective and easy-to-use as tin oxide or zircon. It can be used as an additive to enliven (variegate, crystallize) the colour and texture of glazes (rutile works in a similar manner). In moderate amounts it encourages strong melts, durable surfaces and rich visual textures.
Mechanisms
Glaze Crystallization - Crystallization
TiO2 dissolves into the melt during firing but normally re-crystallizes (or acts as a crystallization catalyst) during cooling (with rutile structure).
Glaze Matteness - Crystal Matte
Titanium can be used in glazes to produce a matte surface with increasing amounts of crystallization in amounts up to 25%. The effect works in most stoneware glazes and is better when the glaze is slow cooled.
Glaze Opacifier - White
Titanium is a crystalline mineral and encourages crystal development during cooling and freezing of the glaze melt. This generally produces opacity. However, titanium opacified glazes have a much different character than zircon or tin types. The latter produces a much more even and bright white coloration. When used as an opacifier the batch amount can range to 10% or more of the recipe.
Glaze Variegation - Titanium
Smaller amounts of titanium dioxide (i.e. 5%) added to coloured or opacified recipes can variegate the surface and make it more interesting (e.g. it alters the shape of crystals, shade of colours).
