Rock Tumbling: What is it?

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Rock tumbling is a popular hobby in Western countries and is also used to produce polished stones for resale. Rough rocks are placed in a tumbler with grit and lubricant, and gradually polished with increasingly finer grain. Moss agate and carnelian are popular stones for tumbling. Preforming can be used to shape rocks before tumbling. A basic rock tumbler kit is needed to get started.

Rock tumbling is a technique by which rough rocks are polished and smoothed. Rock tumbling is a popular hob in the United States and other Western countries, and is also practiced on a large scale to produce large quantities of polished stones for resale.
The process involves taking rough rocks, often of no real monetary value, and placing them in a special tumbling device. The rocks need to be roughly the same hardness so they don’t destroy each other. Some sort of grit and a lubricant are then added as well and the tumbling process can begin. Rockfall usually takes a little over a month and is divided into four or more different phases.

At each stage of tumbling, the rocks are subjected to an increasingly finer type of grain. In the initial stage, rock rolling would use a very rough grit, to remove the rougher edges from the stones. Next, the rocks will be washed and a finer grit added, to begin polishing them. Next, a very fine grit will be added, to remove the last of the edges from the stones. Finally, after washing, the rocks are filled with a polishing agent, such as cerium oxide, and some sort of cushioning agent, usually plastic pellets.

One of the challenges of the process is getting the rocks shaped the way you want. This can mean rolling them much longer than you’d expect, to try and wear them down. It can also mean carving them by hand, in a process known as preforming. In preforming, the stones are cut to roughly the shape you want the finished stone to have. If preforming is used, the rougher stage of the grain can be bypassed altogether, making tumbling a three-step process.

There are any number of stones that can be used, but generally people look for stones that are fairly inexpensive, have striking colors, and have visible occlusions to turn into interesting streaks in the polished stones. Moss agate is one of the most popular stones for rock tumbling because it has a deep green color with blue and white streaks making it very visually appealing. Carnelian is also very popular, with rich browns and reds complementing the greens and blues of the moss agate.

All kinds of strange and exotic stones can also be used in rock tumble, with an emphasis on those that had the strangest shapes within them. Turritella limestone, for example, is popular with hobbyists, as small pieces of shell create amazing and intricate patterns within the polished stone.

To get started in this hobby, you’ll want to find a basic rock glass, of which there are many different designs available at affordable prices. You’ll then receive a few different replaceable barrels for the tumbler, one for each grit level you’ll use, three different grit grits, and a liquid polisher. Within a month or so you should have your first batch of finely polished stones, and you may have found a surprisingly compelling new hob.

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