An accidental change in glaze color or phase due to the nature of the fire or other causes during the firing of ceramics. Later, however, technological advances have succeeded in producing this phenomenon artificially. In a broader sense, not only the hue but also phenomena such as vortex, cracks, and crystals are sometimes referred to as kiln alteration, but this is generally referred to as fire alteration. This is probably due to a very complex and subtle color change caused by the properties of the minerals contained in the clay and glaze, as well as the properties of the so-called oxidizing and reducing embers. The main types of kiln discoloration known so far are the iron black glaze of the Jian kiln type in China and the copper red glaze of the Jun kiln type. Jian kiln tenmoku tea bowls are known for their various hues ranging from deep black to yellowish brown, and for their various mottled kiln variations. The appearance of these mottled patterns is called “hare’s hare,” “partridge spots,” “dripping beads,” “hare’s hair flowers,” “yellow rabbit spots,” “yori,” and “glaze marks,” while in Japan they are called “jasume” and “yohen. The phenomenon of yohen occurs when the reducing gas or volatile matter in the glaze that is contained during firing is released when it escapes through the molten glaze. The glaze is then condensed into a crystalline form, and the crystals form a bubble-sized circle. Unlike ordinary tenmoku-te, which is colored by iron or iron and a small amount of manganese compounds, this type of yōhen-te is also thought to be the result of mixing copper or wolframite, which give off a violet iridescence after firing (see the section on “yōhen”). Soba-te (buckwheat glaze) is a type of iron silicate crystal that is reddish brown or green in color and has an extremely elegant appearance. The latter produced outstanding pieces during the Yongzheng period (1723-35). The former produced excellent ceramics during the Chenghua period (1400-1878), and the latter produced excellent ceramics during the Yongzheng period (1723-35). In addition to the usual purple-red color of the copper glaze, there are a wide variety of other colors, such as cruciferous sand red, fire-back red, pig liver red, eggplant skin purple, leek green blue, firelight blue, and parrot green, depending on the color.
In Japan, cinnabar handware is from the Sung-Gun kiln lineage, and it was most thoroughly colored during the Ming dynasty (1368-1644), showing a wide variety of kiln variations such as festival red, jewel red, pearl sand red, jade red, shohin green, lung red, and milk-rat skin.
