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Rock Tumbler Grit

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Tumbling Grit:

Tumbling grit is sand-sized particles of silicon carbide. That is where the name "grit" comes from. It is an abrasive material that is placed in the tumbler barrel with your rocks. Silicon carbide is much harder than the rocks that you will tumble. When it is caught between tumbling rock particles it creates tiny scratches on them. This continuous scratching wears down the rocks and rounds them. Sharp edges on the rocks are worn down more rapidly than flat surfaces because the grit is rubbing against them on two or more sides. The result of this grinding is smaller, rounded rocks.

There are different types and sizes of tumbling grit. If you bought a rock-tumbler kit, then you will be using what’s provided for your first batch of rocks. After that you will need to purchase the needed grits. The different abrasive grits are described below.

Coarse 60/90, Medium 120/220 or Fine 500?

safety glasses
Protect your eyes!
Safety glasses are highly recommended when working with grit, polish, tumbler slurry or opening tumbler barrels.

Tumbler grit is referred to using the same words and numbers that are used for sand paper. Words such as coarse, medium and fine refer to the size of the particles glued to the sand paper or the size of the grit particles that you will use as a tumbling abrasive.

The numbers, such as 60, 90, 120, 220 and 500 refer to a particle size. They are the opening size, or "mesh" or a standard screen (small numbers refer to larger screen openings or larger particle sizes and large numbers refer to tiny screen openings). Remember to think of sandpaper - small numbers refer to paper with large abrasive particles.

Step 1 - Shape the Rock With Coarse Grit:

The first step of the tumbling process is usually done with 60/90 grit silicon carbide. These are particles that will pass through a 60 mesh screen but be caught on a 90 mesh screen. They are about 1/4 millimeter in diameter - some larger, some smaller. Coarse grit is used because the goal of the first step is to shape the rock. The amount of grit used depends upon the size of your tumbler barrel. We provide some general recommendations below but you might try more or less grit as you experiment with tumbling different types of rocks.

tumber grit chart
This chart shows suggested grit and polish amounts used for different sizes of tumbler barrels. For example: in a six-pound tumbler barrel add ten tablespoons of coarse (60/90) grit for Step 1 of the tumbling process. These amounts are suggestions only. After you get experience with your tumbler and different materials you might experiment with more or less grit and obtain better results. (NOTE: These recommendations are for rotary tumblers. Vibratory tumblers require different amounts of grit and different sizes.)

Steps 2 and 3 - Remove Scratches:

The second step is usually done with medium (120/220) grit which is particles of about 1/8 millimeter diameter. The smaller grit particles cut more slowly than coarse grit. This step does very little shaping or rounding of the rocks. It is done mainly to remove any scratches in the rocks left by the 60/90 grit.

The third step is often done with 500 grit silicon carbide but some people use 500 grit aluminum oxide or a similar-size compound. This step removes scratches left by the medium (120/220) grit, smooths the surface of the rocks and prepares them for the polishing step.

Steps 4 and 5 - Polish and Clean:

The fourth step, or "polishing" step uses a polishing compound such as aluminum oxide which buffs the surface of the rocks to a bright luster. The fifth step is a burnishing step with soap to clean up the rocks and make them sparkle.

Now you are ready for Rock Tumbling Instructions
Rock tumbler grit
Tumbler grit is most commonly a silicon carbide that has been crushed and screened to a specific size. Most silicon carbide grits weigh about one ounce per slightly-rounded tablespoon. Shown above is about four ounces of coarse tumbling grit - enough to process about two pounds of rock in a three-pound tumbler barrel.

Rock tumbler grit
Visual comparison of different grit sizes. The coarse 60/90 grit has a "sandy" texture of about 1/4 millimeter. The medium 120/200 grit is about 1/8 millimeter in size and has a texture like "fine sand". The 500 grit has a particle size so small that you might consider it a "powder".

Rock tumbler grit
Rock tumbler grit is usually sold by the pound and most often is sealed in convenient one to five pound bags. The cost is a few dollars per pound if you are buying in small quantities.

 Rocks and Minerals Commonly Tumbled
Lapis Lazuli
Petrified Wood
Rose Quartz
Smoky Quartz
Tiger's Eye

Rock Tumbler Home Selecting A Tumbler Instructions - Part 1 Instructions - Part 2
Rotary Tumblers Vibratory Tumblers Tumbling Supplies Kid's Tumblers
Rough Grit Polish Media
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