I wonder whether the blade has been exposed to something corrosive or whether it is just bad steel. There was other micro pitting along the bevel that looked similar to what I've seen on older vintage blades not a more modern blade like this. The Focus has a plastic coffin so I'm thinking 1970's but am only guessing.My initial thought is rust. Maybe a bit of surface damage that was enough to cause a bit of corrosion to start
Geez Goose, that's a nice looking hone and should shave FAR better than the first shot. All I can do is shake my head and wonder how he didn't bleed out.....
It's a corrosive substance attacking the steel. A heavy acid or base would be the obvious answer here but you may see it with other substances like high-chlorine cleaners mixed with other chemicals. Do they use something like CLR bathroom cleaner?