The tumbler will be running 24 hours a day for several weeks at a time and needs to be in a convenient and safe location that will not interfere with family activities. It generates a slight humming sound. The motor becomes hot to the touch. This is normal.
Step 1. To load a tumbler barrel, add the correct graded rough rock to about ¾ full, add the grit, and add water so it covers the rock by about ½ inch and seal the barrel.
Step 2. Place the barrel on the rollers and turn on the tumbler. Make sure that the barrel is turning and running quietly – with no squeaks or groans. Check the tumbler periodically to assure that it is operating and not leaking.
Step 3. The tumbler needs to run for 7 to 10 days (in some cases more time is needed for hard rock), 24 hours a day. The load may be checked to see how much rounding is taking place. This depends on the material being tumbled. Soft materials need less run time than do hard materials like agate, jaspers, and petrified wood. If the barrel is opened the seals of the barrel need to be cleaned before reassembly.
In a vibratory tumbler, material loss is much less than a rotary tumbler. About 10 to 15 percent loss and the stones will be angular but polished. For the most part, the procedures are the same as a rotary tumbler except for time, water, and the amount of grit used will be slightly less. About 1 ounce of grit per pound of material or 1 tablespoon per pound. The amount of water is much less. Use only enough water to achieve a good tumbling action. Too much water and the tumbling action will stop and the grit will settle out. Daily checks on the tumbler is a must since the slurry will thicken faster, more water is needed to be added. Run time is also much less. This depends on the hardness of the material being tumbled. Generally, 2 to 3 days per grit will produce polished stones. On the daily check of the tumbler for the amount of water, it gives you time to pull out 2 or 3 stones and wash them to check on how much material has been removed and if they are smooth enough to continue on in the next grit. Longer run times than 3 days will start to give a more rounded surface on the stones. The wash cycles in Steps 4 and 5 above are very important. The amount of water needed for a wash is the amount that produces bubbles with the soap.
In both methods of tumbling, keeping a good record of what is done will help with correcting any problems that arise. Many variations of the general instructions are done. Discussions with other rock hounds or lapidary shops are helpful to correct problems in the art of tumbling stones. More advanced methods are available on the internet or book stores.
The Mohs Scale lists ten minerals according to relative hardness. The scale is graduated from No. 1 (Talc, a very soft stone) through No. 10 (Diamond, the hardest stone).
Use the simple field test below to identify the relative hardness of a stone. Stones in the range of 6.5 to 7.5 will usually polish well.
- Fingernails scratch 2 to 2.5
- Pennies scratch 3.0
- Knife blades scratch 5.5
- Window glass scratches 5.5
- Steel files scratch 6.5
- Garnet scratches 7 to 7.5
- Carborundum scratches 9.5