One of the many questions we get asked about rock tumbling is what size rocks should be used.

While some people are after dainty jewellery, others are after larger pieces to be used as ornaments or decorations.

Unfortunately, rock tumbling isn’t quite as simple as just throwing in whatever rocks you have available and hoping for the best.

There’s a couple of rules which must be followed to get the best from your rock tumbler, including the size of rocks.

The most important thing is to load the barrel with a mixture of rock size and ensure that the largest rock is no more than half the diameter of the barrel.

But that’s not all. Follow these easy guidelines and you’ll be good to go.

The Size of The Tumbler

Rock tumblers vary greatly in size and capacity, so the size of rocks you use will too.

For a 3lb capacity barrel (a good size barrel for beginners), we recommend a mixture of rocks between 0.25” and 1.25”.

Larger tumblers should also be part filled with smaller pieces of rocks, but the maximum size of rock can be slightly larger, up to 2” in diameter.

If you’re unsure, it’s generally best to just stick with the rule above, that the largest rock is no larger than half the diameter of the barrel.

Smaller Particles

It’s important that as well as loading the barrels with rocks you want to be smoothed and polished, you also load it with smaller particles.

These grit particles will remove loose material as they fill the gaps between the larger rocks.

This increases the particle-to-particle contact which will make your tumbler more efficient and mean you are unlikely to have to repeat stages.

Filling your rock tumbler with only large rocks will be less efficient and little grinding will occur.

Ceramic Pellets

Ceramic pellets can also be used as a filler. If your rocks are all the same size, ceramic pellets should be loaded into the barrel to fill in the gaps, to make the tumbler more efficient and increase the amount of grinding.

Ceramic pellets will also distribute the grit around the tumbler, they can be washed between steps and are best used throughout the tumbling process.

Monster Tumbles

Monster tumbles are very large tumbled stones and, although hugely rewarding, the process is certainly a long one!

Larger rocks take a long time to round and smooth, but if you’re patient enough it’ll be well worth the wait.

These rocks should be no larger than half the diameter of your barrel, and you should be careful not to overfill the barrel – one or two stones at a time.

If you plan on creating some monster stones, you should be a little pickier about the original rocks you go for. Rocks with large indentations are a no-no, as they will take a very long time to wear smooth.

Ensure the rock you go for is a colour and shape you like (especially if you are going to be using a vibratory tumbler which will keep the rock’s original shape), as monster tumbles require a lot of time and effort – so you want to create something you’re proud of!