Glaze is a thin layer of vitreous material applied to the surface of ceramics to prevent the absorption and penetration of water or other liquids into the base or for decorative purposes.
Composition] The composition of glaze is not only different between porcelain, stoneware, and ceramics, but also varies widely among porcelain glazes and pottery glazes. However, they are all a type of glass, consisting mainly of silicate compounds, sometimes mixed with some boric acid compounds.
In other words, silicic acid is the most important component of a glaze, and its content can reach as high as 75% in some glazes. The higher the content, the more fusible the glaze. Boric acid is more fusible than silicic acid and is only present in glazes with low firality, and its content is usually less than 10% at most. The most common bases are alkali, lime, lead oxide, and alumina, while others include magnesia, barium oxide, tin oxide, zinc oxide, lead oxide, and antimony oxide. Various metal compounds are mixed in colored glazes as coloring agents.
Types and names of glazes include porcelain glaze, stoneware glaze, and pottery glaze.
The glazes used include feldspar glaze, alkali glaze, lime glaze, ish glaze, salt glaze, lead glaze, zinc glaze, and others, as well as white glaze, colored glaze (celadon glaze, lapis lazuli glaze, black glaze), crystal glaze, pattern glaze, volatile glaze, avalanche glaze, flowing glaze, glaze without gloss, cinnabar glaze, sea squirt glaze, tea gold glaze, and others, according to the color and other conditions of the glaze. Other names are given at the discretion of the place of manufacture, the maker, the creator, etc., so there are too many to count. The most common ones are described in each section.
The most important raw material is silicic acid, which is made from quartz or siliceous rock. Quartz can be lumpy or sandy, and siliceous rocks include feldspar, pegmatite, granite, quartz coarse-grained rock, and other rocks. Alumina also comes from feldspar and other rocks. Some alkalis come from feldspar and other rocks, while others come from nitrite, potassium carbonate, soda carbonate, and borax. Lime comes from limestone, marble, albite, or wood ash.
Adjustment】If the raw materials do not contain soluble materials, they should be weighed, mixed, ground and fine-polished, or, as in the case of conventional porcelain glazes in Japan, the raw materials should be mixed by grinding water separately and then either mortar-polished or not mortar-polished and used immediately. Whenever soluble raw materials are included, they must first be heated and melted together with silicic acid and other raw materials to form insoluble objects, or white balls. Most ceramic glazes are prepared by this method. Various types of mills are used to grind the glaze, but the trommel (spherical mortar) is currently the most commonly used.
Glazing] Generally, glazing is done by mixing water to form a plasma. There are several methods of glazing, including dipping, pouring, coating, and spraying. In the pouring method, glaze is poured over the surface of the vessel, and is used for vessels that cannot be soaked in water or for color glaze separations. The spraying method is used for spraying glaze onto the surface of a vessel using a mist sprayer, and is used to apply glaze to large vessels that cannot be dipped or dazzled. This method has been used in China for centuries, but was poor. More recently, Europeans have been using elaborate mistblowers. Another method is the volatilization method (see “Volatile Glaze”). (The Complete Works of Yaichiro Kitamura on Ceramics)
