Polishing Rocks in a Vibratory Tumbler

Author: Brian Boyle   Date Posted:27 April 2015 

Vibratory rock tumblers, such as those made by Raytech and Tagit, can polish rocks in a fraction of the time required by rotary tumblers. They also result in polished stones that retain the shape of the rough material, as opposed to the rounded shapes obtained by rotary tumbling. On the other hand, vibratory tumblers tend to be a bit more expensive than their rotary counterparts. However, if 'time is money' and you want to retain more of the shape and size of the original material, then a vibratory tumbler may be just what you need.

Materials List

  • A vibratory tumbler.

  • Rocks. You will get better results with a mixed load that includes both small and large rocks.

  • Filler. Plastic pellets are great, but you can use small rocks having the same or lesser hardness as your load.

  • Silicon carbide grit, pre-polish and polish (e.g., tin oxide, cerium oxide, diamond).

  • Soap flakes (not detergent). Ivory soap flakes are recommended.

Procedure

  • Fill the bowl of the tumbler about 3/4 full with your rock.

  • If you do not have sufficient rock to fill the bowl to the 3/4 level, then add plastic pellets or other filler.

  • Add the required amount of SiC (silicon carbide) grit and water. See the table below to get a sense of how much is needed. If you have the instruction manual that came with the tumbler, start out with those quantities. Keep records, so if you make changes you will know the effect the changes had on the polishing.

  • Place the lid on the tumbler and run the vibrator. Let it run for a day or so and make certain that a slurry is forming. Evaporation will occur, especially if the external temperature is hot, so you may need to add water from time to time to maintain the slurry consistency.

  • When the rock has achieved the desired smoothness and roundness, remove the load and rinse the bowl and the rocks thoroughly with water.

  • Return the rock to the bowl, add a tablespoon of soap flakes, and fill the bowl with water to the top of the rocks. Vibrate the mixture for about half an hour. Rinse the rocks and the bowl. Repeat this step two more times.

  • Return the rocks to the bowl and proceed to the next polishing step with the next grit (see the Table).

  • After the final polish step, perform the washing/rinsing process and allow the stones to dry.

Here are some conditions, intended for a 2.5 lb tumbler. You can adjust the quantities for your specific needs. The durations for each step are approximate - check your load and keep records to find the conditions that work best for you. Experiment with different polishing compounds to find the type that works best for your stones.

 Grit Type 

 

SiC

SiC

SiC

SiC

SnO2

CeO2

Diamond

Diamond

 Mesh

 

220

400

600

1,000

---

---

14,000

50,000

 Grit

 Amount 

8 tbls

4 tbls

4 tbls

3 tbls

4 tbls

4 tbls

1 cc

1 cc

 Water

 Cups

3/4

3/4

3/4

1/2

1/2

1/2

1/2

1/2

 Soap

 Tbls

0

0

0

0

1/3

1/3

1

1

 Speed

 

fast

fast

fast

fast

slow

slow

slow

slow

 

 

 

 

 

 

 

 

 

 

Stones

Hardness

Days

 Days

 Days

 Days

 Days

 Days

 Days

 Days

 

 

 

 

 

 

 

 

 

 

Sapphire

9

28

7

7

7

5

---

---

---

Emerald
Aquamarine
Morganite

8

3

2-3

2-4

2

2-4

---

---

---

Topaz
Zircon

7.5

3-8

2-3

2

2

2

---

---

---

Agate
Amethyst
Citrine
Rock Crystal
Chrysoprase

7

0-7

3-4

2-3

2-3

0-3

3
--
--
--
--

---

---

Peridot

6.5

---

2

2

2

---

---

2

2

Opal

6

---

---

1

2

2

---

---

---

Lapis Lazuli

5.5

---

4

3

3

2

---

---

---

Apache Tears
Apatite

5

---

2-3

1-2

1

1
--

---

---
1

--
1
 

*Use a slow speed for all steps when polishing stones with Mohs hardness of 6.5 or lower (peridot, opal, lapis, obsidian, apatite, etc.).

Helpful Tips

  • Make a balanced load that includes for large and small rocks. For a 2.5 lb bowl, sizes from 1/8" to 1" work well.

  • A proper slurry is needed to get the best polish in the least time. If there is too little water, then the thickness of the mixture will prevent proper movement, thus slowing the polishing action. Too much water results in too thin of a slurry, which will result in a much longer time to achieve a polish. The grit may settle out of the mixture altogether.

  • Never wash grit down the drain!

  • Plastic pellets may be rinsed and reused, but you cannot reuse grit.