Tumbling

 

Guidelines for Polishing Rocks & Minerals in a Vibratory Tumbler

The following guidelines are what I have found useful for the Tagit 2.5 pound vibratory rock tumbler. However, these directions should work for other vibratory rock tumblers and for larger loads by adjusting the amounts of grit, water, and soap.

1. Fill the bowl about three quarters full with your desired rock or mineral. It is best to have small and large rocks in the tumbler (1/8" to 1"). If you do not have enough of the desired rock, add a filler such as plastic pellets, apache tears, agates, or any other non-porous rocks that are of the same or less hardness than your desired rock. Why the concern about hardness? If the filler is harder than the desired rock or mineral, then the harder material will polish leaving the desired material which is softer scratched but not polished as well. Secondly, the softer rock will be worn away faster and if that is your desired rock, then you will lose more of it than is necessary. For more on mineral hardness click here. To view an easy to use visual guide in the form of a the mineral hardness ruler click here. Keep one handy near the tumbler.

2. Add the amount of silicon carbide grit (SiC) needed (see Table below), the amount of water, place the lid on the bowl, and run the vibrator for a number of days, checking it every once in a while and adding more water as needed to keep a slurry. If no slurry occurs, which is the case when the grit quickly settles out from the water, then it will take much longer to grind down the rocks or minerals. Too thick of a slurry will result in little movement and little cutting action. Getting a proper slurry is an art more than a science.

3. When the rock is rounded to your satisfaction, remove it from the tumbler and wash the rock and the bowl thoroughly. A Plexiglas screen in a large funnel works well for this operation. The wash water and the used grit should not be put down any water drains, because the grit will clog the drain. Instead, wash the grit into a holding bucket, allow the sludge to settle, and then dispose of the water and the grit separately.

4. Return the rock to the tumbler, add one tablespoon of soap (Ivory Flakes work well), and fill the bowl with water to the top of the rocks. Vibrate this mixture for about half an hour. Again wash the rocks and the bowl, and repeat this washing step twice more.

5. Return the washed rocks to the bowl and proceed to step 2 with the next grit (see the Table below).

6. After the polish step, the last grit in the Table, is completed, wash the rocks with soap as in step 4 and dry.

For best results, a separate bowl should be used for each grit. Graded grits work best, but are more expensive than grits listed as coarse, medium, and fine.

All numbers in the Table are approximate and will vary with the tumbler, load, type of rocks used, and so on.

Note that TiO2, titanium dioxide, is not listed as a polishing agent. While this material is cheap and does a good job of polishing gemstones, it also leaves a white fill in cracks and crevices, which is extremely hard to remove.


TABLE
SUGGESTED CONDITIONS FOR POLISHING VARIOUS ROCKS AND MINERALS IN A VIBRATORY TUMBLER
 Grit/Compound  
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
Stone Hardness
Days
 Days
 Days
 Days
 Days
 Days
 Days
 Days
                   
Sapphire

9

28

7

7

7

5

---

---

---

Emerald

8

3

3

4

2

4

---

---

---

Aquamarine

8

3

2

2

2

2

---

---

---

Topaz

7.5

3

2

2

2

2

---

---

---

Zircon a

7.5

8

3

2

2

2

---

---

---

Agate

7

7

4

2

3

---

3

---

---

Amethyst

7

5

3

3

3

3

---

---

---

Citrine

7

7

4

2

2

2

---

---

---

Chrysoprase

7

---

4

3

3

2

---

---

---

Peridot b

6.5

---

2

2

2

---

---

2

2

Opal b

6

---

---

1

2

2

---

---

---

Lapis lazuli b

5.5

---

4

3

3

2

---

---

---

Apache Tears b

5

---

3

2

1

1

---

---

---

Apatite b

5

---

2

1

1

---

---

1

1

a About half of the volume was polished agates.

b Slow speeds used on all steps.

SiC is silicon carbide; SnO2 is tin oxide; CeO2 is cerium oxide; Diamond is paste that is sold in a syringe; tbls is tablespoon; cc is cubic centimeter.


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