For the tough job
I have to re-profile a large (11" blade) knife made of Japanese blue steel, and it went through one Arkansas, two ceramic, two aluminum oxide, and four diamond bench stones of various grades. Except for the extra coarse diamond stone, they hardly scratched the surface of this knife. Then I saw this extra extra coarse stone from DMT available on KCI, so I bought it, knowing that this probably is my last hope of re-profiling the knife myself without sending it to a knife maker. Yes it got the job done, and for those who don't know the Japanese blue steel, it can be harden to mid 60s on the Rockwell C scale. For reference D2 is typically hardened to RC 60. The only reason I don't give it a 5 star rating is because it developed some rust patches even I clean and dry it everytime immediately after use.