Because of the Japan Current the grain of the stones made from these clams is aesthetically more pleasing. However, because of overfishing, clam shells from Hyuga are scarce, so today almost all shell stones made and sold in Japan are from shells harvested in Lower California, Mexico. Shell and slate stones are manufactured in thicknesses ranging from 7 to 12mm. However, most players agree that a thickness of about 9.2mm is ideal. Yuki stones have clear grains which run straight across the top.
Tsuki stones have grain which curves across the top.
Jitsuyo stones have either irregular or indistinct grain lines. Yuki grade shell stones with the grain highlighted. The photo on the extreme right shows the approximate color of the stones. In choosing a go set, the most important consideration is the balance in the quality of the board, stones, and bowls. If you own a fine tenmasa kaya board, it is aesthetically required that you have the finest set of yuki stones to go with it, preferably ones made from clams harvested in Hyuga.