Rock tumbling and stone polishing is a popular hobby. The most important ingredient to achieving a great finish is time. Polishing is typically a 4-step process involving progressively finer and finer abrasives. Each step is done with a clean barrel, fresh water and a virgin abrasive. The Creetown Gem Rock Museum (in
the UK) has a good outline for polishing stones.
The first three steps require a coarse grit (80 mesh) followed by a medium abrasive (220 mesh) and finally a fine grit (400 mesh). Aluminum Oxide or Silicon Carbide are the preferred media due to their durability and hardness.
The fourth step demands a very fine, hard media that will maintain it's 'cutting' ability for the entire cycle time. Cerium or tin oxide are the abrasives of choice as they will maintain their sharp edges as they break down over time. Sawdust can be added to this step to ease the impact and eliminate chipping of the stones.
Hobby size barrel tumblers will generally have capacities of just a few pounds of stones. Tumbling times for each step is about 1 week. Larger, industrial-grade tumblers such as the MT Series Barrel Tumblers will allow for more weight to be tumbled at one time. This often leads to reduced cycle times and higher production rates. Regardless of the equipment, patience is the key to beautifully polished rocks and stones.
How to Choose Rocks for Tumbling
Not every stone is worthy of the tumbler’s embrace. First, for rock tumbling, select the type of stone that can stand the voyage. Stones that have a Mohs hardness of at least 5 or 6 are hardy enough to withstand some of the rough treatment the tumbling will subject it to. Ones with fractures, pits, or cracks are best avoided, since many times, flaws disintegrate in the tumbling process, leaving unsatisfactory results. Aim for smooth, rounded stones or ones with interesting shapes and patterns that promise a striking finish once polished. Lastly, make sure your chosen rocks are roughly the same size to ensure even wear. It’s a mix of art and science, where your eye for beauty guides the choice, but practicality sets the limits.
The Stages of the Rock Tumbling Process
Rock tumbling is a patient art, taking stones from rough to radiant over several stages. Here’s how it unfolds:
Coarse Grinding: The rocks begin their journey with coarse grit (80 mesh), which scours away the rough edges. This stage is all about shaping and smoothing. It’s rough, loud, and dusty, but crucial for creating a solid foundation.
Medium Grinding: After washing off the coarse grit, the rocks tumble again with a medium abrasive (220 mesh). This step refines their shape, smoothing out the scars left by the coarse stage.
Fine Grinding: The rocks are ready for fine grit (400 mesh), a gentler abrasive that starts bringing out a soft sheen on the stones. This is where the magic begins, with the rocks starting to look polished.
Polishing: Here, the rocks tumble with a very fine, hard media such as cerium or tin oxide. These abrasives maintain their cutting ability throughout the cycle, ensuring a mirror-like finish. Sawdust can also be added to ease the impact and prevent chipping of the stones.
Burnishing (Optional): Some prefer a final stage, where rocks tumble with soap and water to remove any lingering grit residue, adding that last touch of luster. It’s like the final breath before the reveal.
Media Used in Rock Tumbling
Rock tumbling isn’t just about grit. The media you choose plays a significant role in the process.
Plastic Pellets: These little helpers cushion fragile stones, prevent bruising, and help keep smaller rocks from chipping. They also aid in evenly distributing grit during the process.
Ceramic Media: Dense and long-lasting, ceramic media enhances rock tumbling efficiency by providing weight to the load and assisting in polishing. Great for shaping and smoothing stones without excessive loss.
Walnut Shell Media: Often used during the final polish, walnut shells gently buff the stones to a high sheen. An organic choice, it’s softer on the stones yet still effective in enhancing that final finish.
Corn Cob Media: Similar to walnut shells, corn cob media is ideal for a delicate polish, giving rocks that extra sparkle. It’s all about the gentle touch.
Each type of media serves its purpose at different stages, allowing the stones to reach their full glory without a scratch left behind.
Factors to Consider While Rock Tumbling
Rock Type: Do not mix rocks of different hardness levels, as softer stones may wear down faster.
Grit Amount: Adjust the grit to the right amount; an overload can slow down the tumbling, while a deficit might leave the stones unpolished.
Tumbling Duration: Adjust each stage’s length based on the condition of the rocks—some may need extra time, while others may not.
Water Quality: Keep water clean to maintain tumbling effectiveness and prevent dull finishes.
Barrel Load: Avoid overloading or underloading; the stones need enough room to move freely for proper rock tumbling.
Conclusion
Rock tumbling is a blend of art, patience, and precision. Choosing the right rocks, media, and techniques ensures a smooth journey from rough stone to polished gem. The process may seem complex, but the gleaming results make it all worthwhile.
Ready to bring out the natural beauty in your rocks? Explore Kramer Industries’ premium rock tumbling supplies to get started. Contact us today to discover the right tools and media for your tumbling projects!