Naniwa Aotoishi Sharpening Stone - Green Brick of JoyThe Green Brick of Joy The Aotoishi stone from Naniwa has developed a dedicated following among knife sharpeners. The large, brick like shape ensures a long lasting stone and its efficient sharpening has made it a favorite of many. The name Aotoishi, printed in characters on the stone, refers to its color and identifies it as a whetstone. Among its many fans though, the Aotoishi is often simply called "The Green Brick of Joy". General Purpose Stone