Help With Knife Ientification?
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The handle isn't unique. It's not an uncommon type on low-volume semi-custom knives. The only handle in the collection which really identifies the knife is on the Nenox (second from the right), and that's only because of the diamond shape insert.
Small-volume knife making in Japan is often a collective effort involving several shops. It's far more common than not for knives handles to be made and installed by shops devoted to making and installing (wait for it) handles. Some offer a range of options, and I've seen the handle you're asking about on at least a few knives.
FWIW, it appears to be mahogany.
All of the other knives are very la-di-da, so I'd be surprised if the one on the right isn't as well.
You're misusing the word "bolsters." The knife does have a bolster within the casual meaning of the term (hyper-technically you might call it a sintered ferrule); the metal part which seems to swell out of the blade and into the wooden handle. I think you're referring to the handle "pins" (aka "rivets"). The handle may actually be pinned, but with the pins countersunk into holes which were subsequently filled. Not unique, either.
From left to right, they are Masamoto KS; Suisun Inox Honyaki; Takeda AS; something I don't recognize offhand -- and it's killing me because it's not that rare and I should know it; the Nenox S1; and the mystery knife. The four I named are all very expensive, prestige knives. I think the other two are too if only for the company they keep.
I also think that the handle on the mystery knife might be bubinga and not mahogany. Migaki uses bubinga handles which look just like that on their Oishi series, for instance, but I'm pretty sure the knife isn't a Migaki.