GENERAL GUIDELINES FOR LAPIDARY TUMBLING
The following guidelines are general guidelines for tumbling. Your results will vary based on the amount and type rock you are tumbling, the time of each tumble, and your desired results. The condition of the rough material will also dictate how long each step will take. For example, clean stones with nothing encrusted on them will not require tumbling as long as stones with material that needs to be removed from them. Keep detailed notes of your activities and adjust future tumbles according to your results.
Fill the tumbler approximately 2/3 full of stones. Add abrasive. 80 Grit is a popular choice. Stones that are very rough may require a coarser grit. 8 to 10 pounds of rock will take 3/4 to 1 cup of grit. You can add 1/2 teaspoon of baking soda to cut down on gas buildup. Filler can be added (plastic pellets) to help carry the abrasive between the stones. Add water, enough to cover the rocks. Start the tumbler. Check progress after 24 hours and then every 2 to 3 days after that. The first grind should take between 6 and 8 days. After you are satisfied with the first grind, wash and dry the stones completely before beginning the next step. All rough grit must be removed from the stones.
After inspecting stones for pits, cracks, jagged edges, rough edges, etc., place them in the tumbler. Stones with any of the above will need to be rough tumbled again. Stones that are ready for the next step will have to have filler added if they do not make up 2/3 of the tumbler capacity. Same as Step 1 for abrasives and water. The abrasive should be 220 Grit or 400 Grit, depending upon preference. This should take 6 to 7 days. Check after 24 hours and then every 2 days.
Just like before, check all stones for flaws. Set aside any that may need to be tumbled again. Stones that are ready go into the tumbler; add filler to 2/3 full. Abrasive and water are the same. The 600 grit should be used. This should take about 7 days. Check after 24 hours and then after 3 days. 1 to 1 1/2 teaspoons of dry flake detergent may also be added.
After these steps, your stones should be ready for polishing. Cerium Oxide and Tin Oxide are two of the most common all-purpose polishes. Check your stones to see if they are ready to polish by using a polishing buff or wheel. If you have access to any "local knowledge" about the particular stones you are tumbling, they should be able to recommend which polish will work best for the stones.
Polish. After determining the best polish to use, put in tumbler with stones; 8 pounds of rocks to 1/2 cup polish. Most of the time you will need to add plastic pellets for filler in all steps. Be sure that you use unused pellets for the polish step. In some cases, add 1 cup of soap flakes for 8 pounds of rocks and 1 1/2 cups granulated sugar. These amounts can be altered based on the level of the tumbler. All ingredients, stones, and filler should fill the tumbler at least 1/2 to 2/3 full. Polish should take 3 to 4 days.
Please note: These are guidelines only. Please consult your manufacturer's instructions or other publications on rock tumbling for more detailed, complete information.