Quote Originally Posted by David Bassett View Post
I suspect you aren't distinguishing the general "hardness", e.g. HRc 62 (or whatever), or the iron/blade with much harder carbide particles in the high alloy steels which help it hold* an edge and make it harder to sharpen. Lots of threads discuss which abrasives cut which carbides present in which steel. Plain steels, carbon & iron, can be heat treated and tempered to remain very hard, e.g. Japanese blades in White #1 at HRc 65+, and still be relatively easy to sharpen.

(* Warren may drop back in to point out it is an inferior edge that is lasting longer. Depending on what you're doing this may or may not be important. E.g. carbide router bits seem an advantage in MDF, but much less so for delicate hand carvings.)
Yes, I was thinking same thing, David. Andrew seems to confuse hardness with abrasion resistance, which makes analysis confusing. High carbon steels can be harder or softer depending on how they are tempered. I suspect that people with high carbon steels were not getting the highly refined edges with Shaptons that they got with other types of stones and Shapton was trying to solve the problem.