From Yixing Ore to Zisha Clay

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“Each potter has his own secret way of selecting and mixing clay, and will not hand down his secret art to an outsider”.

- Yang Xian Ming Tao Lu (陽羨名陶錄, “Famous Pottery of Yang Xian”) by Wu Qian (吴騫, 1733 - 1813)

Life as we know it could not exist without clay – both in the grand sense for the development of life[1] and in the narrow sense for the development of civilization: clay formed some of humanities earliest cookware, the material for our first structures, and an incentive for technological progression[2]; clay, once refined, was an early artistic material, inspiring civilization to craft sculptural artifacts and later ceramic arts. The path of human cultural development is paved in clay, a human-made material inseparably linked with early industry and art.

Ceramics are a geo-cultural product of semi-deterministic development: surface geology and the availability of ceramic material controlled the types of ceramic wares produced in each region – China developed its ceramic technology, industry, and preferences around the material properties available. Chinese civilization was responsible for much of the progression in ceramic arts, creating splendid works from the early dynastic period through the present day. The clays of China’s vast landmass yielded a range of materials with unique textures, shapability, and coloring when fired. The development of refining processes for ore, glaze formulation, and kiln control created the most advanced and unique wares of each contemporaneous period – arguably including the present day.

Yixing, in contrast to most of the other ceramic centers of China, focused nearly-exclusively on the refinement and processing of its ore into clay without the use of glazes, ceramic over-coats, and enameled surface decorations[3]. Modifying the surface of zisha clay was generally seen by the tea-drinking literati[4] as a betrayal of the natural beauty and functionality of the ware.

Yixing’s ceramic art depends on a variety of skills, from the selection and processing of ore into clay, to the construction of one’s own ceramic-tools, to the hand-building of the clay- shapes, and knowledge of what will survive firing in the kiln[5]. This chapter gives an in-depth overview on the processing of zisha ore into clay; subsequent chapters will further cover the construction and firing of Yixing teapots.

Zisha ore goes through a series of processing to convert ore into clay, and subsequent aging before it can be shaped and fired into wares. In its most simplistic form, the zisha ore is weathered, crushed, and mixed with water to achieve a usable clay, and the clay is then aged to increase its moldability and refinement. Each process requires specialized experience and knowledge to control, yielding largescale changes in the characteristics of the material. The processing method and aging of the clay is likely more impactful on the materials interaction with tea than any input from the artist or firing method[6]; The quality of the clay is determined by the natural quality of the ore – great ore processed poorly will not produce a good pot, while even the most mundane Yixing clay of the Qing or ROC is highly sought after today.

It is generally agreed that clay processing standards decreased with the founding of Yixing Factory 1[7] in 1958. Before F1, zisha ore was usually processed by specialists tied to specific studios or workshops; master ceramic artists worked with ore processing specialists to adjust the processing, blending[8], and age of the clay to achieve specific material qualities.

The following sections of this chapter provides a broad overview of the standard processing method for turning ore into clay, with a discussion of each step[9]: sorting, weathering, milling, sieving, dry purification, mixing & setting, working, aging, and re-working.