How to: Grinding & Polishing of Stones

By Melissa Harr
Polish stones to learn more about geology.

Whether you wish to make rock collecting or lapidary your work or your hobby, you’ll need to learn how to grind and polish stones. Although this process might sound like it requires exertion, a rock tumbler usually does most of the work. As you tumble the stones with progressively finer abrasives, they come out smooth and ready for display. You don’t have to look far for stones to polish, either. Many stones from the beach or the woods will polish. Try to cut the stone with a knife -- if a metallic line is left, then you can polish it.

Shaping

Inspect the stones you wish to polish. They should be of similar hardness. Discard any stones that have cracks or jutting, irregular shapes.

Open the rock tumbler’s barrel and fill with stones until it is three-fourths full. Shake the barrel to settle the stones and add more if necessary.

Pour water into the barrel until the stones are barely covered.

Add coarse tumbler grit. A general rule is to use 3 tbsp. of grit or polish for a 1 1/2-lb. barrel, 4 tbsp. for a 3-lb. barrel or 10 tbsp. for a 10-lb. barrel.

Seal the barrel and turn on the tumbler. Allow the tumbler to run for about seven days, which will grind the stones down into smoother, more uniform shapes.

Polishing

Open the tumbler and rinse out the stones. Examine the stones closely and remove any that are cracked or broken.

Refill the tumbler with the stones and enough water to cover them. Add 220 grit, seal the tumbler, turn it on and allow it to run for six or seven more days.

Open the tumbler and clean the stones and tumbler thoroughly. Add stones and water back into the tumbler and add 500 grit. Seal the tumbler, turn it on and allow it to run for seven days.

Open the tumbler and clean the stones and tumbler as thoroughly as possible. Add stones and water back into the tumbler and add polishing compound. Seal the tumbler, turn it on and allow it to run for seven days.

Take the newly polished stones out of the tumbler. Rinse them thoroughly.

Things Needed

  • Rock tumbler
  • Stones or rocks
  • Coarse tumbler grit
  • 220 tumbler grit
  • 500 tumbler grit
  • Polishing compound

Tip

If the stones do not come out gleaming, try running them through the tumbler for two or three days with a burnishing agent, such as bar soap. Avoid liquid soap, since it can harm both the equipment and the stones.

Warning

Don’t pour leftover slurry or grit down any household drains because it will clog as it hardens. Instead, pour the slurry into a milk carton and throw it away.

About the Author

Melissa Harr is a writer and knitting pattern designer with a range of publication credits. Her latest work includes blogging for Smudge Yarns, judging fiction for Ink & Insights 2015 and creating patterns for I Like Knitting magazine. Harr holds a Bachelor of Arts in English from the University of Illinois at Chicago and a CELTA.