A method of firing porcelain with a high luster by sealing the lid of a saggars made of the same clay as the product. The saggars are made of the same quality clay as the product, the lids are well matched, the contact areas are fully glazed, and the inside of the saggars are glazed slightly lower than the glaze of the product, and the product is then placed inside and fired. In this process, the saggars are sealed before the glaze is melted to completely block the permeation and diffusion of gases from inside and outside. The result is a beautiful product with a luster like a jade. This method was invented by Kiheiji Tsuji of Hizen Arita during the Bunka period (1804-18), and it is said that he used this method to produce vessels to be presented to the imperial family. In Kyokushin-yaki, after firing, the saggars are crushed with a mallet to remove the product. In other words, saggars are used only once and require a lot of work, so this firing method is not used except in special cases. (“History of Arita Porcelain Industry,” Terauchi Shinichi)
