The pattern on the cups are called crazing. The glaze reveals this unique pattern of crack that occurs from how the clay and glaze shrunk in different rate throughout the making process. Then, sumi ink, a charcoal based ink is applied to darken and compliment the crazing across the milky white body. 

As the craze allows the color of the liquid that is held inside the cup seep through between its micro-fine lines, the pattern will turn deeper in color as the cup is used overtime. You may notice a "pinging" sound until the initial crazing process settles down, but this is not a sign of defect or cracking.

Item color: White