National Geographic Instructions


National Geographic Tumbler Instructions

These directions will help you operate your National Geographic tumbler to learn about the geology wonders of rock. You will discover the material science of rocks and run your machine properly to produce wonderful small gems from rocks to use as jewelry or other decorative items. You can discover the materials that make up the planet and from them create beautiful smaller tumbled rocks.

This small rotary rock tumbler operates differently because of its size. There is a precise and small amount of media that is required. Also the stones have to be of a smaller size due to barrel capacity.

Success Key is Primarily Rock Choice

In similarity to other rotary models you will generally be following  the most common instructions for general rock tumbling in Rotary Tumblers. Many variations can be found in regard to tumbling instructions that make adjustments for different tumbling equipment and different types of rocks. The most important tips are standard. Your tumbler manufacturer may have specific instructions for your tumbler. Presented here are general guidelines and the most common consensus on tumbling methods. You might find the rock hardness information helpful on the Mohs Scale reference.

We Offer a Pre-measured Grit Solution

Be sure to see our grit kit designed specifically for National Geographic tumblers

You will see in some of our kits that offer extra items, some additional steps and guides to the tumbling process.

Good Rock Selection

The tumbling process starts with good rock selection. Pick rocks that are of the same hardness and similar size ratio (the biggest should be no more than twice the smallest) to coordinate their development in the tumbling process. Gather enough rocks to fill your barrel between 2/3 and 3/4 full. Avoid using unusually odd and non-rounded shaped rocks with the more common rounded shapes as these will be more difficult to sculpt.

Four Step Process

Rotary tumblers use a four step goal oriented tumbling process:

  1. Coarse Grind
  2. Medium Grind
  3. Pre-polish
  4. Polish

Between each of the four steps remove, thoroughly rinse your rocks, clean out the barrel and remove any grit or rock debris. This is really important as the coarser grits from one step will act adversely in proceeding steps,scratching rocks as you are refining them with finer media. As always, it is advised not to throw used grit down a drain as plumbing will be damaged. Use a bucket and a screen to collect used grit and slurry.

Step One (Coarse Grind)

The goal of this step is for all surfaces of your rocks to be well-rounded.Place rocks in the tumbler and add the 60/90 silicon carbide grit. You are looking to round your rocks in this step over 7 to 10 days. The Grit to rock ratio here is 2 tablespoons of grit per pound per pound of rock. Add water until it is just below your top layer of rocks. Seal the barrel and invert it to check for leaks. Once the tumbling starts watch for a few minutes to be sure there are no leaks. Proceed with tumbling, and at the early days if this step, check daily on the progress by opening and inspecting the barrel. If the barrel appears to physically swell, open it to vent the buildup of gas which may naturally occur, be prepared with safety glasses and precautions for that. You can also add a teaspoon of baking soda to prevent gases.  Examine  your rocks and slurry (the grit and water now mixed with some rock trailings). If it seems thick enough to impede the smooth tumbling of your rocks, thin it with a small amount of water.  Some of the rocks may be now too small or too odd to continue working with them, so you will remove these rocks. As for the rest, once you see rounding has occurred for most or all of your rocks this move on to step 2.

Step Two (Final Grind)

In this step your purpose is to conclude the shaping process to your satisfaction. You will be removing and declensions and pitting that may have been present after step one.This step usually takes 7 to 10 days also. You have already removed rocks that are not responding sufficiently or have evolved to an unattractive shape. Put your cleaned rocks in the barrel again, add a 120/220 silicon carbide grit in the same proportions as in Step One – 2 tablespoons per pound of load. Add water up to the bottom of the top layer of rocks and, if you had any problem with gas buildup last time, add a pinch of baking soda. Seal and tumble as before. Your slurry should be a little thinner than in the last step varying with the softness or fragility of  materials your are processing. Your goal again in this step is to see that all the scratches from the first step are ground away,  and the rocks have a smooth, matte finish. Using a magnifying glass may help check for smoothness.

Step Three (Pre-polish)


In this step the goal is to make the rocks extremely smooth. As always start as with Steps One and Two, put cleaned rocks in the cleaned and fresh barrel to make a full load. Use a pre-polish of either silicon carbide 500 or aluminum oxide 500 for this step, about  1 tablespoon per pound of load, and then add water up to the bottom of the top layer of rock. Tumble time here is up to 7 days, with more checking slurry consistency and general progress every day or two. You may be pulling some of the rocks out earlier than others as they will become smooth sooner and even show some luster.  For softer rocks, you may need to do a second pre-polish step or just keep them in a little longer. At the end of this step it is most crucial to really clean the rocks and barrel which will be more difficult as you are using a finer grit. This is so important because any grit can ruin the progress of your rocks in the final polish step.

Step Four (Polish)

By this time your rocks are looking pretty good and ready for that lasting final shine. You have been extra diligent on cleaning the rocks and barrel. Place your rocks in the tumbler and add Aluminum Oxide Polish, about 1 tablespoon per pound of rock.  Step four takes up to seven days but be sure to check the rocks as you are proceeding because some will be finished earlier. The best check for completed rocks is that they look as now as they would if wet. Once that is the case you are done with this step. One final detail, its best to clean up now by cleaning your equipment thoroughly before everything dries and encrusts. So you'll be ready for your next project with rock tumbling.

In addition to the instructions above, it may be beneficial and interesting to see our section on the Science of Rock Tumbling. This is a behind the scenes look at the technical and scientific foundations of the rock tumbling process.