Glaze Types


The Effects of Fluxes


Fluxes affect the melting point, color and texture of a glaze.The following will be briefly described under each range—Earthenware, Mid-range, and Stoneware:

  • Characteristics of color, durablity, etc.
  • Fluxes most often used
  • Most common types of glazes in that range

Earthenware (cones 015-1)

  • Characteristics
    • brilliant colors possible
    • often not durable enough for food serving
  • Fluxes: Borax, Gerstley Borate, Colemanite, Lead, or Strontium.
  • Some Common Types
    • Luster—a thin film of metallic salts that are reduced either by the medium that holds them when being painted on, or introduced in the very low temperature firing. It is usually applied to an already glazed surface.
    • Majolica (maiolica)—traditionally an opaque tin-based glaze with very colorful painted designs. It began on the island of Majorca in Spain, and then was adopted by Italy. Also called Faience for Italian city where it thrived.
    • Overglaze / China Paint—ceramic enamel colors painted on a fired glaze surface and fired a second time (at a lower temperature than the first glaze firing, allowing bright red/orange that would burn out at a higher temperature.)
    • Raku—a firing process that usually includes post-firing reduction to alter the soft glazes with an exaggerated crackle, metallic luster, or opalescent effect.
    • Terra Sigillata—a very soft slip glaze originated by the ancient Greeks.
    • Underglaze—oxides or commercial glazes or stains, painted under the glaze layer before firing.

Mid-range Glazes (cones 2–7)

Characteristics

  • More brilliant colors possible than in the stoneware range
  • Colors similar to reduction effects may be obtained
  • Often durable enough for food serving
  • Economically fired in an electric kiln

Fluxes: Some low-fire flux is substituted for high-fire fluxes.

Benefits

  • Many potters use this range because it produces some of the benefits of the stoneware range, but also allows a wider range of color.
  • A second, and great, benefit is that many people find electric kilns more easily available and economical to use. Electric kilns normally do not fire above cone 6-8, and have an oxidation atmosphere. Even without the glaze effects possible with reduction in a gas kiln, the mid-range is an excellent alternative firing range.

Resource: Electric Kiln Ceramics: A Potter's Guide to Clay and Glazes, Richard Zakin

Stoneware Glaze Types (cones 8-13)

Characteristics:

subtle colors
can be durable enough for food serving

Fluxes:

Feldspars, etc. Go to The Flux Pool for a list.

LINKS: http://Matrix2000.co.nz/GlazeTeach
http://digitalfire.com

Some common types:

  • Celadon—a transluscent glaze first developed in China to imitate the color of jade, from the colorant iron.
  • Chun—a pale blue opalescent glaze developed in China, made in low alumina wood ash and feldspar glazes with small percents of iron and copper.
  • Copper Red(sang de bœuf, flambé)—an oxblood red created with a small percent of copper in certain reduction glazes.
  • Crystalline Glaze—snowflake-like crystals can form in certain low alumina glazes with careful heating and cooling. Glazes often run and should be fired on stilts over a saucer.
  • Salt or Soda Vapor Glaze—salt is introduced into a hot kiln causing it to vaporize. The sodium attaches to the silica in the unglazed clay body creating a glaze, often with an orange peel textured surface.
  • Shino—an almost purely feldspathic white, pale iron red, gray, or marbelized glaze first produced in the Mino kilns in Japan, in 1580. It has a thick, very slightly transluscent surface that is desirable in Japanese tea ceremony bowls.
  • Slip Glaze (vitreous engobe)—a glaze that contains a large percentage of clay. The advantage is that it may be applied to greenware rather than bisque to eliminate one firing.
  • Tenmoku (temmoku)—a rich dark glossy iron-saturated glaze developed in China and Japan.