Starting with a very coarse sand-like material, and moving through three more stages of ever-finer grit, it will take your tumbler only four to six weeks to accomplish what it takes Mother Earth years (if not centuries) to do. To really understand how tumbling works, just think about how you would go about sanding a flat surface. You would start with a very course sandpaper and progress to finer and finer sandpaper until the surface was very smooth. Tumbling simply adds water (and a third dimension!) to the process.