tell me about Japanese " blue steel"?

Last but not least. Since the japanese kitchen knives are highly hardened and the steels are not as tough as you may be used to, they can be sharpened only on japanese waterstones. I tried to sharpen a blue steel kitchen knife on the sharpmaker once and that was not a good idea. The whites with very light pressure are ok, but the grays will destroy the edge.

While it's true that Japanese waterstones have been the traditional way to sharpen these blades, they are certainly not the only way to do so. Diamond Hones (DMT makes these among other companies) and 3M Abrasive Films are very effective at sharpening even very hard Japanese steel.

If one wishes to take it to the next level beyond mere stones, then stropping with chromium oxide, diamond pastes or 3m abrasive films will get you in the area of 60000-10000 grit. It's beyond my needs but some like to push their blades to utter perfection.

I personally use the DMT Aligner and have all the stones from x-coarse (220 grit) through xx-fine (8000 grit). I reprofiled my Japanese blades entirely using this system. It took a little time but it was easy enough. One can easily get a razor sharp edge using DMT products - diamonds are vastly harder than the hardest Japanese steel. Just use very light or no pressure and water to lubricate - let the diamonds do the work for you.