A mirror is a rounded, concave surface of a teacup that has fallen out. Kumagawa teacups generally have a mirror, and those without a mirror are called “kagami-shikiri” (mirror forgetting). Many katate and other so-called Koraimono have mirrors. The top disk of a potter’s wheel is also called a mirror.
Mirrors” are often seen in China, Korea, and other countries. They appear to have been made by pressing down hard on the inside of a prospective vessel to prevent the bottom from cracking when forming it.
The lower the kaolin content of the clay, the harder it must be tightened to prevent the base from breaking. To prevent this, the clay was tightened with a spatula or other tool. Later people probably referred to the remnants of this process as “mirrors.
