The term grit is thrown around loosely and it is very hard to get a correct measurement when everyone is using a differen chart. Using micron's as a measurement will give you more accuracy as there is only one size possable. All stones will also cut differently leaving different types of finishes for similar "grits" diamond stones for example will never yield the same finish as a waterstone because the abrasive particals are different in shape. The diamond stones particals being sharp and jagged and the waterstones being more round and smooth. The finish may appear different but the final edge sharpness is all pretty close, though each edge will cut differently in respect to what meida it was sharpened on.
I'm not taking it personal I just know better.
You'll never get to the bottom of it. Too many standards. Some rate on the largest particle, some on the average particle. 1/2 micron diamond dust is sold as 60,000 mesh and also as 25,000 mesh, and would be about 30,000 JIS grit in waterstones.
Here is a microscope shot of some 3M 15 micron silicon carbide finishing film
Okay, what dimension is 15 microns? Look like a lot of irregular hunks sort of like crushed potato chips.
Here is a spyderco UF rod
Average grit looks to be about 2,000 JIS but the particles are not sharp like the SiC film... very rounded like ceramic burnishers. The finish it leaves is similar to the Lansky blue hone but seems to have more galling (pulls up balls of metal out of the surface that smear and dig ruts and streaks) At best I think it leaves a finish similar to an 8k waterstone, but with streaks and gouges that prevent it from making a good polishing stone for mirror finishing any sizable surface.
Garnets in Belgian Blue and yellow coticule stones are like 20 sided dice... round with shallow corners so they dig very shallow, wide V's in steel and leave a finer finish than the micron size would indicate. AlO and Chrome oxide are shaped more like little quartz crystals or foot balls and leave a rougher surface than garnet. SiC, if sintered so the grit can't contour to the work piece, just gouges the heck out of things, but if used loose, so the shards can lay flat, can produce a very smooth surface since the flatish plates will tend to slice off high spots in the steel (which is why it is used on a soft lap to finish metalurgical samples so their crystal structures can be examined under a microscope)
Diamond plates cut fast but leave a very chewed up surface because quite a number of the crystals were floating higher than average when the metal plate hardened and froze them in place. The high floaters will eventually break off to the average level of the rest of the diamonds as they break in but until then, they act like they are coarser than they should be (I have a 15 year old ez-lap 1200 that leaves a finish similar to a King 1000 grit stone, but it is broken in to the point that many people would consider it worn out, and still leaves too many scratches for polishing). Loose grit on a strop will leave a much better finish than a plate.
and the finish quality is excellent for the grit/mesh.
