I've been primarily using two knives for the past couple of weeks. Both knives are KU, one Yamawaku nakiri and the other a Carter IP KU gyuto. Both knives performing are beautifully, other than one major problem...they have developed a light rust throughout the entire KU portions of the blades.
I'm very familiar with carbon blades, and I'm really quite anal about how I care for them. My three other carbon blades I use (SK4, I believe, Swedish Carbon, and white 2) have zero rust, and other than a tiny spot that popped up on my Misono, I've never had an issue with it before.
My wife came up with a hypothesis that perhaps the softened water (salt pellets added into the softener, if I'm not mistaken) that I have been forced into using to wash the knives due to where I'm staying throughout the week could be to blame.
Has anyone had this happen/does anyone here use carbon blades an have a water softener? I'm wondering if my smart (and pretty) wife might just be onto something.