Hyuga Tokusei Hon Nachiguro No. 30 Clam Shell Go Stones - Hyuga Clam Shell Go Stones - Model: Hon Nachiguro No. 30 - Usage: Practical Use The black go stones are dry and appear powdery. Washing them with a neutral detergent, removing the moisture, and then wiping them with natural oil will restore their black color. Here's what I found on Google: The Nachiguro stones (black stones) of Hyuga Tokusei Clam Shell Go Stones may appear whitish when the gloss oil applied to prevent surface dryness dries out. Condition: If the surface of the black stones is white and dry, it means the oil has dried. Treatment: Before use, wipe them lightly with a cloth. Wiping will restore the black luster. If you want to add more shine, wiping them with a cloth containing a small amount of plant-based oil, such as camellia oil, will further enhance the luster. Thank you for viewing.