I recently aquired a set of Asano stamped nagura, together with a tomo nagura (from a reputed vendor) and have been using the stones as prescribed.

However, I have since noticed that my Ozuku Asagi (a very hard and fine stone) has scratches on its surface which weren't there before. Pretty annoying.

I'm a bit disappointed as I know the naguras are supposed to be softer stones and the vendor purposefully sent me a softer stone than my asagi for my tomo nagura...

Has anyone else experienced this and can anyone suggest best course of action?