Ever wondered how to selectively polish parts of a stone while leaving other areas untouched? This video breaks down an ingenious method using hot glue and a tumbler to create unique stone specimens.
Polishing only a part of a stone in a tumbler (or how to make specimens with a tumbler). See comments for details.
byu/WonderfulRockPeace1 inRockTumbling
This is a great technique if you want to highlight specific features of a stone while maintaining a natural or rough texture on other parts.
The key to this process? Hot glue! By applying hot glue to the areas of the stone you don’t want to polish, you can control which sections are exposed to the tumbler’s grinding and polishing action. Here’s a quick breakdown of how it works:
- Apply Hot Glue: Add hot glue to the areas you don’t want polished. Keep in mind that smooth or shallow surfaces don’t hold glue well, so avoid those spots if possible.
- Tumble with Other Rocks: Only about a quarter of your load should contain rocks with hot glue, as too much glue could affect the tumbling process.
- Wash Between Stages: Carefully wash the stones between tumbling stages to remove slurry and grit. Be gentle—washing too aggressively can loosen the hot glue.
- Reapply Glue if Needed: Sometimes the glue will peel off during tumbling. Simply reapply if needed.
- Use Sugar for Cleaning: Adding sugar to the final polish stage helps wash away any grit or slurry trapped on the stones’ rough surfaces.
The video also covers what materials and tools work best. Hot glue is recommended because it’s rubbery and durable, whereas other coatings like crazy glue don’t hold up well. Additionally, rotary tumblers are more likely to cause the glue to detach due to their intense action, so using a vibratory tumbler, like the UV18, might be a better option for this technique.
This method is great for selectively polishing stones and bringing out the best of both polished and natural textures. Once the tumbling is done, simply peel off the hot glue (soaking the stone in hot water helps if it’s tough to remove). The end result? A one-of-a-kind stone specimen with stunning contrasts between polished and unpolished areas.
If you’re interested in experimenting with stone tumbling and creating unique rock specimens, this video is full of tips and tricks to get started!
Detailed Notes and Instructions:
(Taken directly from the original Reddit post)
Briefly:
- Add Hot glue to the parts you don’t want to polish. The surface cannot be too smooth or shallow.
- Add with other rocks. No more than 1/4 of your load should have hot glue.
- Wash the stones carefully between stages. Sometimes the hot glue will come off and needs to be reapplied.
- The use of sugar, especially in the polish stage, helps to wash away any slurry/grit on the stones.
More detailed:
- Other types of coatings (eg. crazy glue) have not worked for me. Hot glue is a little rubbery and doesn’t wear away quickly. Smooth and shallow surfaces do not hold the glue well and it will peel off/become detached. Rotary tumblers are especially prone to causing the hot glue to come off.
- Since the hot glue surface is rubbery/spongy, it does not provide a good surface for grinding and actually adds quite a bit of cushioning to the tumble. There will also be potential contamination from grit (both embedded in the hot glue and it gets between the hot glue and the rock). Grit contamination is somewhat minimized in a vibe, as I believe the grit gets in easily but gets stuck on the rock. Since vibes are run moist (but not submerged in liquid) there is not a lot of grit/slurry coming out. Regardless, a majority of the stones in a tumble shouldn’t have hot glue. Ceramic media is fine to use.
- The rocks need to be washed carefully (I use a garden hose). Washing too aggressively and trying to remove all of the slurry/grit will loosen the hot glue and could lead to it coming off. Not enough, and you have the potential for too much grit contamination. The hot glue can be removed between stages and reapplied so that there is little carryover but it hasn’t made a big difference for me and adds a lot of extra work. Sometimes, the hot glue will come off by itself during a tumble.
- Once the tumble is finished, the hot glue can be removed simply by peeling it off. If it is difficult to remove, scoring with a blade and then ripping/peeling along the score mark works. Also, soaking in hot water to make the glue more pliable helps. Sugar really makes cleaning the polish off of the stones easy as there will be a lot trapped on the rough surface of the stone.
Notes:
I have not done this in a rotary-only tumble and have only completed batches in a UV18. For this batch, I did 1 week with 36 Silicon Carbide grit in a Thumlers Model B. Then 2 days with 220 Aluminum Oxide grit in a UV18 and then 1 day in Aluminum Oxide polish. For stones with a clean cut (minimal to no saw marks), the rotary step can be skipped. For stones that have lots of saw marks, they will have to spend time in the coarse stage in a rotary. The edges will start to round off in a rotary. A little hard to tell, but this can be seen in comparing polished rock 4 to rocks 5-7.
