Clay in the raw state obtained from the place of origin (deposits) have a variety of colors beige, yellow brown, red brown, gray, and black, the color differences are influenced by the ratio of the levels of ingredients include a mixture of clay or dirt humus (organic ), iron oxide (Fe), manganese oxide (Mn), cupper oxide (Cu), cksida cobalt (Co), etc..
At the time of the combustion process that is both organic impurities will be burnt, while the materials are chemically bonded to cause the clay to color. In general, the most widely Earthenware clay contains iron oxide (Fe).
Form of granules or particles that will provide smooth and soft plastic bending properties or if it contains water that serves as a lubricant. Earthenware clay plasticity is high enough so that the dry shrinkage and shrinkage grilled too high, so the higher the plasticity of clay higher the dry shrinkage and shrinkage fuel. Another trait is high enough porousitasnya after experiencing burning process and this is because the clay still contains a lot of sand.
Given the porous nature allows water forming out of the ceramic body during the drying process so that the ceramic objects are not easily broken or cracked.
Earthenware clay structure changes from the combustion process:
- Fuel temperature between 700 0 C-900 0 C to break easily
- Fuel temperature between 900 0 C 0 C-1050 safe
- Fuel temperature between 0 C 1050 1180 0 C maximum
- Fuel temperature above 1180 0 C will burn even melt.
Ceramic stoneware usually on average fuel at cone 4 – cone 11 (11860C-13150C), so it has a temperature of maturity among Earthenware and Pors elin. Stoneware clay bodies known as good because of its strength, has natural colors, are hard and somewhat mengkaca.
As well as porcelain, stoneware if burned at a temperature where the clay into mengkaca then the result will be watertight, but generally not too mengkaca stoneware. Cook and glaze stoneware body at the same temperature so that it will form a glaze perfect accuracy.
The types of stoneware that developed in Europe in 1600 and 1700 using cobalt oxide and manganese to make black stoneware, agateware (also called marbleware or variegatedware) is an artificial agatestone and produced with a combination of dyes of different clay in a single body .
Stoneware in the past usually generated and natural clay containing feldspar and silica which is burnt to be solid and not porous. Natural clays such as fireclay, clay pipes for water and clay to make bricks can be used directly without much additional material as needed and can be used for the formation of the hand or round.