Ad Hoc Tumbling Group

Ad Hoc Tumbling Group Message

No Meeting in April

The allure of a perfectly polished, vibrantly colored rock is undeniable. But achieving that mesmerizing sheen through the art of rock tumbling isn't just about the grinding and polishing stages in your tumbler. The secret, often overlooked, lies in the very beginning: smart rock collecting.

Think of it like this: A sculptor wouldn't choose a cracked and flawed block of marble to create a masterpiece. Similarly, selecting the right stones from the start dramatically increases your chances of tumbling a batch of truly stunning gems. You can apply this to all the lapidary arts.

So, what makes a "right" rock for tumbling? It all boils down to minimizing imperfections. Here's why:

Rocks with deep pits and cracks present a challenge. These imperfections will require significant grinding to remove, drastically reducing the size and shape of your stone. You might end up with a tiny pebble instead of the statement piece you envisioned.

Those same cracks and pits are notoriously difficult to polish to a smooth, even sheen. They can trap grit and polish, leading to uneven surfaces and a frustratingly dull finish. Despite all your efforts, you'll be left with a rock that still feels rough.

Rocks with internal fractures are much more likely to break during the tumbling process. The constant abrasion and impact can exploit these weak points, leading to a batch of fragmented failures instead of gleaming successes.

How to Choose the Right Rocks in the Field - When you're out exploring for potential tumbling candidates, keep these tips in mind:

Visual Inspection is Key: Carefully examine each rock for cracks, pits, and other surface imperfections. Look closely, even use a magnifying glass if you have one. Avoid rocks with large or numerous flaws.

Density Matters: Rocks that feel heavy for their size are generally denser and less porous, making them better candidates for tumbling.

Consider the Hardness: Different minerals have different hardness levels, which affect how they tumble. It's generally best to tumble rocks of similar hardness together to ensure even abrasion. If you're unsure, a quick scratch test (using a steel nail, for example) can help you gauge relative hardness.

Think About Shape: While you can certainly reshape rocks in the tumbler, starting with a relatively smooth, rounded shape will save you time and abrasive grit.

In essence, the key is to be selective. Don't grab every rock that catches your eye. Take the time to examine potential candidates and choose those that are already relatively smooth and free of major imperfections. By making smart choices in the field, you'll be setting yourself up for rock-tumbling success and a batch of beautiful, polished stones that you can be proud of. So, get out there, explore, and remember: a little bit of selective collecting goes a long way!

As the 2025 Tumbling Contest winds down, we look forward to seeing the beautiful gems our contestants submit. Stop by the Tumbling display at the Mother's Day Show to see the winners. Remember, contestants, the deadline for returning your entries is May 1st.

The Ad-hoc Tumbling Group meets via Zoom on the 3rd Tuesdays of January, March, May, July, September, and November. We discuss tips and tricks for rock tumbling. As always if you have any questions or suggestions for the tumbling group, you can email them to

Tim Hellinger
Co-Chair (co-chair open volunteers)