Rotary Rock Tumbling: Loading the Barrel

Part 3 of 6 – loading the barrel for best results

In the last section we talked about how to properly sort your materials by hardness and cleavage type, and now in this section we offer pro-tips and advice on how to fill your tumbler with successful results in mind. This includes not only the proper amount and sizes of rocks to add vs. barrel capacity, but also good advice on the various types of cushion media that our members rely on and recommend.

What follows next in no specific order is a bullet list of pro-tips, tricks and advice on the subject of proper loading of your tumbler barrel, contributed by the Rock Tumbling Hobby Forum community.

  • Try to load the barrel with a mixture of rock sizes from larger to smaller if you can. To achieve this, if every rock you are starting with is close to the same large size, you should consider purposely adding smaller pieces of rock scraps or ceramic media to the barrel to fill in the gaps between rocks and increase the effectiveness of the grit rubbing against the surface areas of the larger stones.
  • Do not be afraid of having too many smaller stones and or ceramic filler media filling in all the gaps between your chosen rocks. Aim for using a range of filler sizes anywhere down to even a 1/4 inch in size to ensure maximum cushioning and contact which carries abrasive grit to all surfaces of your tumbling rocks.
  • Having a mixture of rock sizes and fill in the barrel also helps encourage what we call a good ‘waterfall’ tumbling action inside of the barrel as it turns. This helps ensure a uniform grind across all of the rocks.
  • It is very important that regardless of the weight size of the barrel, or what your tumbler instructions say, fill your barrel by volume to 3/4 full, no more no less. Any more than this and the tumbler is too full and the rocks will not have enough room to move and tumble correctly. Any less than this and the action inside the barrel will resemble a rise and fall and will not achieve enough rock-against-grit rolling action.
  • Although it can be expensive, purchasing at least one extra barrel and devoting it to the polishing step of the tumbling cycle is a pro-tip that you will begin to understand over time. Doing this provides maximum effectiveness in preventing grit cross contamination which can cause less than perfect results.
  • Depending on the hardness of the rocks or fossils you are tumbling, be creative with your filler media and add stage specific tumble media like plastic pellets to help cushion the rocks. This is especially important as the rock sizes decline opening up more space in the barrel and allowing rocks to hit hard, potentially causing late stage damage.
  • Be creative and try various options for media. Pea gravel from your local home store or website can be used as a media with harder stones, and is an inexpensive option compared to the cost of ceramic media. To go along with this, glass marble vase fillers work well with soft stones as they are the same hardness as natural obsidian.
  • Plastic beads, non-abrasive ceramics, sugar, agar, sylium husk, clay, newspaper, sawdust, and corncob are all notable for potential use as cushioning media. Any of these products mentioned, even when used in combination do provide cushioning between the rocks but ceramic will actually assist in the polishing process, making it a favorite media for vibration tumbling as well.
  • Special types of materials such as crystals (quartz/amethyst), obsidian, and fossils may need even more cushioning in the barrel to help prevent cracking or excessive volume loss. This is why it’s so important to know the characteristics of your material before you load the barrel.
  • Filler media such as plastic pellets or ceramic pieces should be bought by the pound in bulk, and avoid purchasing small prepackaged media that appear to have been designed with your exact situation in mind. These fancy looking products are designed for nothing more than to separate you from your money. Check Amazon or Ebay and get the best deal you can on a 5 lb bulk bag of pellets or NON-ABRASIVE ceramic media chips.
  • If you decide to use ceramic media, it’s very important to purchase “non-abrasive” ceramic because abrasive ceramic has SiC (silicon carbide) grit embedded in it which turns each little ceramic piece into a grinding stone, and that’s not what we want.

Now that you have loaded your rock tumbling barrel with carefully selected rocks and media, it’s time to add water and grit, so check in on Part 4 of this series first: Rotary Rock Tumbling – Adding Water and Grit because there is more to it than it seems.

If you would like to offer feedback about your own experiences, pro-tips, tricks and advice, please post in this thread in the Rock Tumbling section of the RTH Forum, and they might eventually make it into the appropriate category in this article series.