Stay safe everyone!
When you load the barrel:
STEP 1 - Coarse Grind - 60/90 grit silicon carbide
STEP 2 - Medium Grind – 120/220 grit silicon carbide
STEP 3 - Fine Grind or Pre-Polish – 500/600 grit silicon carbide
STEP 4 - Polish - Aluminum Oxide, Tin Oxide, Cerium Oxide, TXP, Raybrite are all types of polish you can use
If your stones have a smooth surface but do not shine, they might need cleaned up with soap. We sometimes run our cleaned rocks in the tumbler with powdered laundry soap for a few hours, this gets all polish residue off of them and brightens them up. If they have scratches on them, the rocks will need to go back to STEP 2 and repeat the process from there.
Start with quality rough to produce quality tumbled stones. Rocks that are fractured will break while tumbling and scratch other rocks. Discard it or break it along that fracture before it is placed in the barrel.
The tumbler barrel should be loaded with rocks of mixed sizes. If you only have large rocks, then you should add some smaller rocks, they are needed to carry grit to all of the surfaces of the larger rocks. Each batch that you tumble should have at least 25% small pieces.
Tumbling works best when all of the rocks in the barrel are about the same hardness. If soft rocks are tumbled with harder rocks, the softer rocks will wear away quickly and they will never take a polish, only the harder rocks in the batch will polish.