Collected Information on Rock Tumbling

Hand Polishing

By Alan Silverstein,
Last update (this page): March 16, 2008

This being a website about tumble-polishing the following section doesn't really fit, but someone asked me so I wrote it up and might as well save it here... "Extra credit."

I was wondering if you could describe your (hand) polishing technique.

Nothing fancy, I own a 10" Tagit diamond dropsaw (slow but functional for cutting ends where needed), a Richardson's Rock Ranch high-speed dry sander, and a Richardson's leather buffing wheel. These are all bolted down in the garage where I occasionally find time to go play during warm-enough weather.

The rock saw is useful for initial smoothing of an end where required, but it takes patience, and it does not produce as smooth an end as a good automatic saw would. It's hard to avoid saw marks (crescent-shaped indentations). Then again you can use it to hand-pre-form the convex surface a bit if desired.

The dry sander is effective but tricky to use compared with wet diamond or silicon carbide wheels -- you must avoid overheating the rock, and also breathing the dust. (Note, all three pieces of equipment together cost about the same as one Diamond Genie...) I keep a bowl of water right below the paper sanding wheel (which is upside down, you hold the rock up to it) and dip it every few seconds. The water on the end of the rock also gives you some idea where you are hitting as you work the convex surface. I wear a dust mask or for longer sessions a respirator mask.

It's nearly impossible to get a good shine in the center of a perfectly flat end, or (with the rubber disk on a Richardson's sander) even to keep the end perfectly flat. Every stone ends up domed at least a little.

Sanding sheets are about $1/each. Unfortunately they cut great for a minute or so when fresh, then have a long mid-life where they work OK but are prone to be slow, cause heating and spalling, etc, before they wear out. Anyway I go through coarse (60), fine (220), and two levels of prepolish sheets. I keep a table lamp aimed at the work and often wear a binocular magnifier for close inspection.

I'm a perfectionist, but especially with irregular rocks like fossil wood you eventually say "good enough" and go on. I aim to remove all visible scratches, but a perfectly regular convex surface without any pits or cracks is hard to achieve.

Finally the rocks are polished with cerium oxide, wetted with a spray bottle of water, on the polisher. I keep a shower cap over the leather wheel when not in use to keep it uncontaminated. I feed the wheel fresh oxide by wetting the end of the stone with the spray bottle, pick up a little cerium powder, then "dress" it onto the wheel (previously wetted too) and get to polishing. A little cerium goes a long way.

The Richardson's buffer lets you apply a lot of force before it stalls. I do this being careful not to catch an edge and fling the rock out of my hands. Sometimes with softer stones you can actually correct many prepolish sins with several minutes of high-pressure polishing.

The cerium sticks to the rocks in crevices, etc. I get rid of it by water spray pressure, toothbrushing, soaking in soapy water, etc.