Glaze is a thin, glass-like film that covers the surface of a piece of pottery. Most of the pottery we use in our daily lives is covered with glaze. Glaze not only gives color and luster to pottery and makes it look beautiful, but also prevents water penetration and stains from adhering to the surface, making the ware durable and easy to handle.
In Japan, kilns came into use in the 5th century Kofun period to fire vessels at higher temperatures. When fired in a kiln, the ashes from the trees used as fuel fell on the surface of the vessel, and the ashes melted in the fire to produce a glossy, glassy quality. This was the beginning of glaze. Such glazes made from naturally falling ash are called "natural glazes." Vessels coated with natural glaze became impervious to water and greatly improved in durability, which subsequently led to the development of techniques for making glazes by mixing various raw materials, and vessels were fired with glaze on their surfaces.
Since glaze would cause the vessel to fall apart if applied to a vessel that had just been shaped by hand or on the potter's wheel, ceramics are basically fired twice. The general flow of pottery production is as follows: molding, drying, unglazing, glazing, and firing. The unglazing process is necessary to make ceramics strong enough to withstand glazing, and many other processes are involved in the production of porcelain. "Shino" and "Oribe" glazes made in Seto City, Aichi Prefecture, are representative of glazes born in Japan, but today's glazes vary widely, from shiny and matte to milky and translucent, with different expressions depending on the clay used, raw materials, ratio of the preparation, and firing method.
There are also unglazed ware. Bizen ware and Tokoname ware, which are among the six oldest kilns in Japan, have a particularly strong image of yakishime. The Bizen ware "Ichiyougama" sold in our store is also made without glaze, and is produced by firing a kiln for 10 days and half a night with 10 tons of split red pine wood after forming the pottery on a potter's wheel, after making the clay from locally available clay. Because the pots are not strong enough without glaze, they are baked at a higher temperature for a longer period of time than usual, thus achieving such high strength that there is a saying, "Bizen mortar that does not break even when thrown."
If you learn about the origin and types of glazes and the reasons why they are applied, you will probably change the way you look at the vessels you usually see. When you look at vessels in a store or visit a pottery production area, you may discover something new.
Yamatada Katoen's Natto Bowl
手島敦『釉がわかる本』 双葉社 (1999)
江口滉『陶芸入門 原料から完成まで』 文研出版 (1973)