Polishing Petrified Wood in a Rock Tumbler
Polishing Petrified Wood in a Rock Tumbler
Petrified wood is fossil wood in which the original organic material has been replaced by minerals, often silica, over a very long period of time. As a result, a piece may still clearly show growth rings, grain or fibre structure, while polishing behaves like stone.
Petrified wood is fossil wood in which the original organic material has been replaced by minerals, often silica, over a very long period of time. As a result, a piece may still clearly show growth rings, grain or fibre structure, while polishing behaves like stone.
What is Petrified Wood?
Much petrified wood consists largely of chalcedony or quartz. The original cell structure of the wood can be preserved during the mineralisation process, which means that after polishing you may sometimes see exceptionally sharp wood patterns. Colour can range from cream and brown to red, black, grey and yellow.
Hardness
The hardness is around often approximately 6.5 to 7. That tells you a lot about which stones you can safely combine.
Suitable for the rock tumbler?
Good silica-petrified wood is usually excellent for a rock tumbler. However, quality varies greatly. Compact, fully mineralised material can shine beautifully, while porous or partially weathered pieces may retain pits and dull areas.
Can petrified wood go in a rock tumbler?
Good silica-petrified wood is usually excellent for a rock tumbler. However, quality varies greatly. Compact, fully mineralised material can shine beautifully, while porous or partially weathered pieces may retain pits and dull areas.
Petrified wood can often be tumbled with agate, jasper and chalcedony if the material is compact and hard. If you are unsure about a porous piece, it is better to tumble it separately.
- Keep beautiful natural shapes intact as much as possible.
- Brush grooves and small cavities clean between stages.
- Use ceramic media with irregular pieces.
- Combine only stones of similar hardness.
- Check dry for fine scratches before polishing.
Polishing Petrified Wood: step by step
Never rely on time alone; inspect the surface after each stage. A stone that still has sharp edges, deep pits or clear scratches is usually not ready for the next grit. You can also find the general process in our step-by-step guide to polishing stones.
Inspect the wood structure
Choose pieces where the interesting grain is not only in a thin outer layer.
Remove rough and weathered areas
Let step 1 run long enough to remove the soft crust and sharp edges.
Assess porous areas
Open fibres or holes can trap coarse grit. Clean them extra carefully.
Polish for contrast
A well-polished surface can make growth rings and grain much more visible.
Important: clean the barrel, lid, rim, stones and media thoroughly before moving on to a finer grit stage. A few leftover coarse particles can cause new scratches in a later stage.
Which grit should you use?
For many tumbler stones, a progression from coarse silicon carbide to increasingly finer grits works well, followed by a pre-polish and polish stage. The required tumbling time depends on the stone, the starting shape and how much material you want to remove. See the current range of grit and polishing media.
Coarse grit shapes the stone
The first stage is intended to round off sharp edges, remove weathered outer layers and grind away small imperfections.
Fine grit prepares for shine
The final grinding stages remove the scratches from the previous grit. Polishing compound only works properly once the surface is completely smooth.
Which stones can you combine it with?
Petrified wood can often be tumbled with agate, jasper and chalcedony if the material is compact and hard. If you are unsure about a porous piece, it is better to tumble it separately.
Hardness is not the only criterion. Brittleness, cleavage, porosity and existing fractures are just as important. Two stones can be about equally hard and still behave very differently in the same barrel. When in doubt, a separate batch is safer.
Common problems
| Problem | Likely cause and solution |
|---|---|
| Wood grain stays dull in places | Some areas are more porous or have been mineralised differently and therefore take on less shine. |
| Grit gets stuck in holes | Use a small brush and plenty of clean water before moving to the next stage. |
| Beautiful pattern wears away | Grinding with coarse grit for too long can reduce characteristic edges or structures. Stop once the shape is right. |
How do you recognise good starting material?
The quality of the rough stone determines a large part of the final result. Prefer compact pieces without deep open cracks, loose crust or strongly grainy areas. Porous stones can hold grit, and crumbly pieces can produce sharp fragments that scratch other stones.
Suitable
Solid, compact, no loose crust, no deep open fractures and a size that fits the barrel well.
Less suitable
Very thin protrusions, porous areas, soft weathered skin and cracks that are almost open already.
Polish stones yourself?
With a good rock tumbler, sufficient filling and the right grit, you have the most control over the result. Take enough time, especially in the coarse stage: what is not solved there will usually show up again later.
Frequently asked questions about Petrified Wood
Is petrified wood really wood?
It is fossil wood whose original material has largely been replaced by minerals.
Can petrified wood go in a rock tumbler?
Yes. Well-mineralised, compact petrified wood is often very suitable.
Can it be tumbled with jasper?
Usually yes, as long as both materials are compact and have roughly the same hardness.
Why do some parts not become shiny?
This is often due to differences in porosity or mineralisation within the same piece.