Just received a pair of 1500 diamond stones, “lightly used”. They do look lightly used, although, who knows. Thing is, when I ran my fingers over them, I could feel nubs on them. Maybe that’s why the prior owner didn’t like them. At any rate, rather than using them that way, I worked them over the edge of a scrap plane iron that I use for testing. After working them for just a short time, I was able to get rid of most of the nubs or clumped stones, which is what I assumed they were. Now the stones feel very smooth when moving over an edge.
Now…did I do the right thing or did I ruin the stones? I figured, the amount I worked them was probably equal to about 1, maybe 2 knives and a plane iron is no harder than a knife, so I thought it would be ok.