With the large straightening whetstone from the Japanese knife manufacturer Kai, whetstones are smoothed again. This means they can be used for considerably longer. It is almost the same size as the standard whetstones used for knife sharpening.

Run the rectifying stone over the stone in a figure 8 motion until the desired result is achieved. The rectifying stone (also known as a levelling or straightening stone) smooths out depressions or unevenness in the surface of the whetstone used and rounds off its rough edges.