I have used his steel, too. The price seems higher than Dictum, but with lower shipping and no duty fees, it isn't much more.
A few tips on using Hitachi san-mai billets:
1) Profile the entire blade before doing any tapers or bevels. Clean up the profile to 220 grit or finer along the blade edge and spine.
2) Dip the blade in 3:1 to 5:1 FC and rinse well. You will see a black line where the core is. It isn't nearly as wide as one might think ... usually about 1mm ( .040"). It only takes a few seconds for the etch to blacken the high carbon core. The plain iron will stay white, or only slightly darken.
3) From tip to plunge, grind an edge bevel at 45 degrees. Take it down until it is touching the black exactly. This will center the core down the edge. Etch again to check that the core is centered.
3) Distal taper has to be kept to a minimum or the core will come out too far along the tip.
4) Start the bevels and take them down to a FFG with the core just touching the san-mai sides along the edge. Do a little on one side and a little on the other. Sneak up on the edge until both sides have the bevel just touching the core. Etch as often as needed to check. You want the grit to be 220 by this point.
5) Take the bevels down with 220 or 400 grit (slower is safer) until the core shows along both sides evenly as a 1mm ( .040") stripe when you etch. Sand a tad, etch, rinse, sand some more. It will take some time, but you should be able to get it pretty even on both sides.
6) The core should have an edge about .020"-.030" wide now. Any further adjustments should be done only with 400 grit. Hand sanding at this point is almost a requirement unless you are really skilled at the grinder.
7) HT with a quench in Parks#50. Temper twice at 400F for an hour each. Water quench between tempers. Slower quenchants ( canola and such) may not harden the edge sufficiently. Water/brine can be used by the brave hearted, buy I far prefer Parks #50 or any similar fast oil.
8) Be aware that the sides are still soft steel, as they are plain iron. Even the suminagashi san-mai is fairly soft. The sides will sand down just as fast after HT as before, so don't hogget crazy or use any coarse grits. Hand sanding with a hard backing block is by far the best idea. Take the bevels down to a near zero edge, switching sides often and etching regularly to keep the dark edge lines as even as possible. It will walk farther away from the edge at the thinner tip than along the belly edge. Just keep it as even as possible from side to side. Take it to at least 800 grit and you are done. Don't attempt to polish the san-mai sides, as they are soft and won't take a good polish or stay that way.
9) Finish the knife and when everything is done, sharpen at a fairly low angle. I use 12 degrees per side as a rule. This will make a VERY sharp edge in the hard steel. Once the entire knife is done and the edge is sharp, you can slice a lemon a couple times to re-darken the hard metal. It will darken in time on its own, anyway.
10) Oil the blade well to prevent rust spots and pits.
