Recently I got Iwasaki Western Tamahagane, which is deferentially heat treated razor. Knowing that I decided I'll etch it with acid to make the Hamon stand up from the rest of the blade.
After a few soaks in hot vinegar and cleaning in between, and natural stone polish afterwards I got a pretty interesting hamon to show up.
Then the big surprise...
I was working on a FON Golden Star, from my "for restoration" stash, hand sanding to prep it for high mirror finish. I started with Aoto powder then 1k Aluinum Oxide powder, and saw that the steel of the blade has two distinct finishes meeting ~1/2 way -a sure sigh for a differential heat treatment.
So I put the blade trough the hot vinegar etch process and got a nice wide hamon. Whet I found really surprising is that a factory made razor has this kind of treatment, may be that was the way to achieve really high hardness of the edge. Needless to say this one stays in the collection, and I will have to check every single Japanese straight for hamon from now on
So there ya have it- Honyaki Straight Razors.