Hi guys,
I see there is an interesting debate happening that I can miss:) I am a professional full-time sharpener at SharpEdge and I sharpen daily a lot of different knives, also a lot of ZDP-189.
In fact, I gave this Bunka to my wife last year and I can explain some simple facts. First, about the brittleness. It is brittle, and my wife would be the first to tell the tale, as she doesn't care much about the proper usage. She opens cans, cuts through bones, basically all the things you shouldn't do.. :) Probably because I can (and do) repair her knife all the time..But still. comparing it to other, shirogami and similar steels, it's actually not so terrible, like VG-10 or so. The knife is still here and holds an edge:)
Sharpening - I sharpen the Bunka by hand on whetstones, steel rods are out of option (think ceramic rods), but on stones, there are no problems. With normal sharpening stones of medium/high quality and basic sharpening knowledge, there are no issues sharpening it.
20% of Chromium should be more than enough for normal steels to get it pretty much stainless, but with powder steels, like ZDP-189, it's a little bit different. With normal use, this Bunka will not develop a patina. In more extreme situations it can get a very light patina, but only with chefs like my wife, who truly ignore all knife maintenance tips.
Let me give an example. My wife's Bunka got some small spots after cleaning the fish on the beach in a bucket full of a salty water, and then she left it overnight not wiping or cleaning it at all !!!:( Also, after cutting a large number of lemons, we didn't clean it too... But don't worry, I just cleaned the knife and rubbed it with a cloth and it was nice and shiny again. In short, we abused the knife and we didn't get to see it rust.
And one more thing about the ZDP-189 steel and its performance. I sharpen all the knives from our kitchen arsenal, but this black beauty stays sharp looong. Very long. And that's the beauty of powder steels! Try it.
Luka