Black spots

Looks like another Mora (in fact like my blue handled one) you could sand them off with sandpaper (wet & dry normally a black colour)start at 220 and work up as high as you can get at least to 2000 grit

Good job there – bet you had to clean off the Japanese carbon rapidly .
Incidentally someone told me that leaving acidic deposits on knives such as from -onions – fruits -peppers- tomatoes will actually take some of the sharpness away – its sounds possible since even though the acids are weak they must have some effect upon a thin edge so rinse quickly .

I have a favorite hunting knife I made some years ago of D2, hardened to about RC 59-60. One year I sharpened it to what I considered my best effort with a Spyderco Triangle Sharpmaker, but didn’t get to use it that year. The following year I proudly handed it to our guide to unzip my pronghorn. After a few seconds, he handed it back to me, saying it wouldn’t cut worth a ****. I was shocked (and embarrassed)and handed him my Buck 110, which had been recently sharpened.

Why did the D2 knife lose its edge?? The edge showed no wear, but it was clearly not sharp. It was kept in a soft leather sheath I’d made from a hide with a really rough inside. Was there maybe acid in the leather?

I once worked in a tannery and know that they use alkaline baths to dehair and deflesh the hides. Ammonia maybe, but no acids.