I recently purchased two diamond sharpening stones from amazon. One of them was a medium grit (600) and the other was a fine grit (1200). They arrived in the mail about a week ago. When I unboxed them I noticed that neither one was labeled for its specific grit, and to the touch, they both feel exactly the same.... How do I figure out which is which? I haven't used them yet... Would I be better suited just giving them both try and see which one puts a finer polish on my chisels? I guess that should tell me, but any suggestions would be greatly appreciated. By the way, they are not the DMX diamond sharpening stones, they were the "Ultra Sharp II Diamond Stone Kit - Medium and Extra Fine". In fact, I am actually looking at the product on Amazon right now, and the one's in their picture clearly are easy to tell apart just by looking at them.... Do you think they might have sent me two stones with the same grit by mistake?
If I were in your situation, trying to figure out the grit of some unmarked diamond stones, I would get the iron out of my plane, put it in the angle guide, and mark the edge of the blade with a sharpie.
Then I'd see how many strokes it took to remove the sharpie, and I'd check frequently to see if I could discern any linear marks from the abrasive. On coarser grits you will see some linear marks but at high polish grits you'll just get a mirror surface.
Compare the results with some different grits of sandpaper and you should be able to get a reasonable idea of how the stones will function, if not precise grit counts.
Some diamond plates use color to identify. Lacking that use a Jewller's loupe (magnifying eye piece). I must say years ago I moved to using Japanese water stones. They are made by King as well as others. NOTHING else works better. They cut fast in coarser grades ( 700 - 1200) and polish to a mirror in fine grades ( 5000 - 10000 ) even with years of experience I found they are better than Diamond. One reason is they slowly wear away into a thick slurry which not only evens and lubricates the cutting, but constantly exposes new sharp grit.