The early porcelain ware was produced using a once-fired process. The blue designs were drawn directly on dry greenware then covered with a translucent glaze. The pieces were then glaze fired at 1300°C.
Colored over-glazes were developed in the mid 17th century. Lord Nabeshima, licensed the over-glaze techniques to artisans in his domain, which included the Arita area. This allowed him to restrict the dissemination of the trade secrets of over-glazes.
Bisque firing was introduced in the late 17th century. With this process, the green ware was first fired at 700 - 800°C. Designs were then painted onto the bisque ware with a pigment called gosu. Gosu is an unrefined mix of cobalt oxide, sodium and other minerals mined in China. The cobalt gives Imari its distinctive blue designs. After decoration, the porcelain was covered with a clear glaze then fired again in the kiln at 1300°C. The twice-fired process greatly improved the quality of porcelain ware.
Soon, fine Japanese porcelain wares became recognized and highly appreciated by Europeans. In 18th century large quantities of porcelain were produced according to European specifications and exported from the port of Imari, in northern Kyushu. Thereafter, blue and white porcelain came to be known as Imari.
While colored Imari was in high demand both inside and outside Japan, blue and white Imari developed into a highly sophisticated art form within Japan. Many of the Imari artists were heavily influenced by the Kano school of sumie painting. During the latter half of the 18th century, the art of blue and white Imari reached its pinnacle. The quality of the wares from this era cannot be matched today. These porcelain wares were exchanged as gifts among feudal lords and wealthy merchants. By the middle of the 19th century, porcelain was utilized for every day use in the homes of the common folk.