A glaze in which the ashes of plants and trees are used as a fluxing agent. Ashes were generally the most important raw material for glazes in Oriental ceramics, but the demand for ashes has greatly decreased since modern times, when limestone and lime stone were always used as substitutes for ashes. However, ash glazes are still valued because of their extremely elegant glaze tones, a quality that cannot be attained using glazes made of limestone or lime stone. There are many types of ashes used in Japan, China, and Korea, and each production area uses ashes of local plants and trees. In Japan, there are countless types of ashes, including chair ash, barrel ash, ash, ash, chestnut bark ash, incense ash, yuzu ash, yangban ash, cedar ash, pine ash, wood ash, earth ash, konya ash, bamboo ash, and ashes. These ashes are made by removing the alkali salts from the ashes obtained from burning plants and trees, and at the same time, removing the cinders and other impurities. The various types of ashes mentioned above have their own characteristics, and all have slightly different properties, but they can be divided into three main groups: chair ashes, earth ashes, and ashes. (i) Chair ash: This type of ash is made by burning special plants and trees for the purpose of making ash, so it is relatively pure and contains little iron. There are many types of ash that belong to this category, such as zelkova ash, orange ash, etc. Of these, zuish ash is the most representative and has the best quality and is also the most expensive. (2) Earth and stone ashes: These are obtained after the use of firewood, and are mainly composed of miscellaneous woods. Since it is a waste product of fuel, it is prone to contamination by earth, stones, iron, etc., and is very impure. Recently, the quality of the product has generally declined, and some of the products are so contaminated with coal ash that they cannot be used at all. Earthen ashes contain a large amount of iron oxide and manganese oxide, which are coloring agents, and their glazes are yellowish brown when oxidized, and pale blue-green or brownish green when reduced. (3) Straw ashes are the ashes of siliceous plants and trees, usually called straw ashes, which are made by burning rice pills and then grinding and watering them. Because it is difficult to burn the carbon content during the burning process, straw ashes are usually dark black in color and resemble charcoal dust. Ash also belongs to this category. Straw ashes are generally mixed with clay ashes and used as milky white opaque luster glazes. While these three types of ashes can be classified into the above three categories, there are many other types of ashes that have properties in-between these three types. The major difference between these ashes and other raw materials is that they contain phosphoric acid, which is thought to have a significant effect on the glazes of old ceramics that used ashes. (Report of the Ceramic Testing Laboratory, Science of Old Pottery, Basics of Glaze Formulation)
