Chromium-plated Kanna

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I recently got my hands on a really cool new kanna blade which has been in development for several years by one of Japan’s greatest kanna blacksmiths. It was developed in an attempt to create a blade that lasts a long time between sharpening sessions but can achieve a level of sharpness capable of cleanly shaving one of the most challenging woods here in Japan; sugi (Japanese cedar, cyrptomeria). The blade is a plated with a super thin coating of chromium on the ura side, and unlike most kanna blades, the ura side is never meant to be put on a stone. Instead only the bevel side of the blade gets sharpened.

I’m far from an expert on metallurgy but my understanding is that chromium is an incredibly hard metal, much harder than your typical hagane, and since the layer on the ura side is only 1 micron thick, that thin layer of super hard metal effectively becomes the cutting edge. And it’s hardness allows the blade to cut considerably longer than a standard kanna. In fact unlike every other blade that I’ve ever used, this blade apparently will get slightly sharper after a bit of use. Since the chromium is harder than the steel below it, the steel will actually start to wear away behind the edge of the blade leaving an even more acute edge than when first sharpened. With a typical kanna as you are planing, the wood is rounding over the edge of the blade little by little with each pass. But since chromium is so hard it takes a much longer for that rounding over to happen, meanwhile the steel just behind the chromium starts to wear, forming a keener edge.

That’s the story from the tool seller anyhow. I have yet to put the blade to use, but I’m pretty confident that all this will hold true. The blacksmith who makes these blades is incredibly fastidious and has a reputation for doing incredibly high quality work. He’s also been developing these blades for the past several years doing lots of testing to see how these planes perform.

All that said these planes do sound kind of delicate. I believe they can be used with an ura-gane (chipbreaker) but there’s also a danger that tapping in an overly tight ura-gane could damage the ridiculously thin 1 micron thick layer of chromium. Rust is also a real danger, since any rust that develops, if it creeps in between the chromium and the steel, could cause the chromium coating to start flaking off. So it sounds like these blades require more caution in use than your standard kanna.

But I’m still super psyched to try out this plane. I have to make a dai for it first, and I’m thinking I’ll make one with an adjustable brass insert at the mouth, keeping it a single blade plane. So stay tuned. I’ll follow up with more once I have a chance to put this new wonder to use.

P.S. Here’s a shot of the sharpened edge. This is how the blade came to me, pre-sharpened, I believe by the blacksmith, who uses a micro bevel sharpening technique that is nearly identical to the method I’ve posted about several times on the blog. Notice the horizontal scratches formed by the course grit stone, and the vertical scratches (micro bevel) produced by the finish stones.

And here is the blade itself, a 42 mm wide blade. Currently the chromium plated kanna is only available in small sizes, with this being the largest size available.