When describing what a real Yixing teapot looks like, many collectors are at a loss to put into words what distinguishes a real Yixing clay (zisha) teapot from other clay teapots; they just know when they see and feel the teapot for themselves.
Fortunately, Besides the texture and color of the teapot, there are a number of signs or ‘imperfections’ that can be looked for to indicate the authenticity of an Yixing Teapot. There are four kinds of ‘imperfections’ which can be found on true zisha: 1) Tiny white spots; 2) Tiny black spots; 3) Tiny holes on parts of the surface; 4) Tiny bumps on the surface.
Tiny White Spots (Mica)
Zisha contains many naturally-occurring minerals including: hydromica, muscovite, kaolinite, quartz, hematite, iron oxide, silicone oxide and others. Their inclusion in the clay and the firing temperature of the teapots (generally between 1050°C - 1280°C) give it its special appearance.
The tiny white spots are trapped particles of mica. Mica will not vaporize below 1280°C, so these spots are a common characteristic of the surface of Zisha teapots.
Tiny Black Spots (Tierong)
The tiny black spots are called Tierong 铁熔 in Chinese. They are caused by the melting and separating of iron from the clay during the firing process at a high temperature. The iron forms small black spots on some parts of the surface of the clay. These iron spots should appear as tiny spots that are scattered few and far between. If the surface has a great many black spots crowded together, it’s a sign of low quality.
Tiny holes on the surface (Tiaosha)
If you look very closely at the surface of an Yixing teapot, sometimes you will be able to see a few very tiny holes. They are so small and few that they can go unnoticed.
These holes are called Tiaosha 跳砂 which translates to “jumping sand.” This is a result of the sand-like character of zisha. When firing in a kiln, all zisha will shrink in size to a certain extent, during shrinking, some larger grains of zisha on the surface of the teapot are sometimes squeezed until they pop off of the surface, leaving a tiny hole. This is a sign of true zisha, unmixed with other kinds of clay.
Tiny Bumps on the surface (Baozi)
Tiny bumps, found scattered on the surface of zisha, are called baozi 爆子. These bumps are caused during firing in the kiln when the size of the teapot contracts. Some larger grains of zisha inside the surface of the clay are squeezed and pushed out towards the surface of the teapot. These grains are blocked by the surface clay, which is pushed outwards forming a bump.
All four of these ‘imperfections’ are in fact indicative of authentic zisha. When found together they indicate a very high likelihood that the clay is authentic pure zisha (not mixed with non-zisha clay). Since these characteristics are very difficult to fake, they are used as a guide to evaluate the authenticity of Yixing teapots.