3 Easy Ways to Polish Agate - wikiHow
3. Pour the coarse-grit carbide inside the tumbler. Tumblers put rocks through 4 stages grinding: coarse, medium, fine, and polish. Start with the coarse carbide to grind down the rough outer layer. Scoop in the instructed amount of carbide. The amount of grit to add depends on the size of the tumbler you're using.