Naniwa abrasive powder works very well to help flatten whetstones quickly. Using a small amount of the silicone carbide, along with your stone-flattening tool, will work quickly to get your whetstone to the desired flatness.
Naniwa is a well known manufacturer of high-quality, synthetic whetstones and tools that aid in cutting, grinding, sharpening and polishing professional as well as home use knives and other cutting tools.
