That gessweincanada.com chart matches the one I got from Advancedabrasives.com almost exactly. It lists 15 micron as being equivalent to 1200 grit and 9 micron as being equivalent to 1800 grit. When I switched to film, the 15/9 films effectively replaced the 1200/1600 ceramics. The scratch patterns look extremely similar and I feel that the film is more consistent.
There’s been some discussion (see cwbx’s link Confused by 3 micron diamond stones) about bad scratches with the 3 mu diamond stones. I don’t have a pair, but I’ve had some experience with breaking in a set of 800/1000’s which revealed some freakish clusters of grit standing proud of the surface. The clusters were oriented parallel to the stone, so they resisted normal break-in and continued to produce really bad scratches well beyond the normal break-in period. It was when it badly chipped my ZDP Delica that I finally did an inspection and found the offending clusters. I clamped up a short section of plate glass and worked the edge for maybe ten or twenty strokes at normal pressures and the clusters were gone. I imagine the possibility exists for similar problem with the 3 micron stones.
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