Just how i classify or grade rocks from rough grit to go or not go to next grit. This batch had more really gouged up rocks that I knew would take a long time or need extra help to progress.
I find that using the mud to show me the bad spots works the best. For a couple years, I had been washing them off, then trying to look at the scratches with magnifying glass etc. Figured I’d post a boring video to show how I now do it. I strive for as-close-to perfect polished rocks as I can get, which all starts with the rough grind being complete. Basically, you can feel many of the faults by touch, not all, but a lot, so as you grab one, start feeling around it for faults.
Lake Michigan rocks, all found by me, I run mixed batches. Lortone rotaries, then finish in Lot-O vibe. This is just for stage 1, rough grit, 60-90 is what I use. By “grinder”, i now have a cab machine to use, but previously used dremel with diamond bits to grind crevices/craters out enough to allow other rocks to work that area.
Then I restart a batch again, adding new rocks or wait for the ones that need machine ground to be added back, to the perpetual rough grind process.