Japanese whetstones (also called water stones) – both natural and synthetic – are known for their quick-working qualities, not only for Japanese blades, but also for their Western equivalents. The small particles that do the cutting are loosely bound together in the stone, and so during sharpening with the whetstone, the surface particles are quickly washed out, allowing new, sharp, particles to start working on the blade. These whetstones must be lubricated only with water! Never use oil or other lubricants!