Reverse bent Yarri Kanna
This small masterwork of Japanese craftsmanship in steel is best suited to working arched or convex surfaces.
One would at first glance think that it would be difficult to sharpen this tool. But it is not more difficult than a chisel or a knife. In principle it is the same as sharpening the normal Yarri Kanna.
The cross section of the blade is simply a triangle, consisting of two bevels and a polished flat side. To sharpen the flat and the two facets, use a small rounded stone (photos in the Japanese waterstone section). Use the handle to clamp the tool securely, so that the stone can move unhindered over the edges of the Yarri Kanna. After a certain time a light ridge or burr of steel will form on both edges of the flat side. A consistent movement with the sharpening stone will result in a consistent burr and tell you that you are doing the job right. Always follow the form of the blade with your movement. The burr can be removed on a flat fine-grained honing stone.
It is more dangerous to move a sharpening stone over a blade than to move a blade over a stone. When you work the edges with a small contoured stone, remember that you can easily give yourself a deep and nasty cut. This is true not only during sharpening, but also when one is working wood with the Yarri Kanna. One should always pay close attention to minimising the risk, by concentrating and working carefully in a quiet environment.