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In the first part I talked about how I managed to fuse up a slab from black and whites offcuts of glass.
In this post I will continue with details about cutting the slab into cabochons, grinding the edges and then the final fire polishing of the cabochons.
Sorry, no photo of the slab before cutting. You will have to use your imagination using the cut pieces as your guide.
The slab was about 200mm x 100mm in size. It was cut up on my modified diamond tile saw. You will find other posts about how I modified this to cut small pieces safely.
The pieces varied in size but were around the 20mm x 30mm in size. After cutting, each piece was ground to remove the saw marks and to make all four sides parallel. A couple of pieces were left as is regards their sides, just so I had a couple of variations.
You can see the result of this preparation in the photo. I included a few other cabochons the also need fie polishing.
Everything was cleaned and then fired on a shelf prepared with Bullseye standard kiln wash. This was not a full fuse. Just enough to contour the edges and give the pieces a nice polish. The firing schedule is below.
Although the cabochons all rounded and polished well, the devitrification and staining remained on most cabochons. That glue, I am sure.
You can see in the close-up photo this happened only on the white, so the white is also partly to blame.
Anyway, to fix this I then placed everything in a tumbler and tumbled for near 7 hours. My intention was 6 but other things got in the way and it was 7 hours before I stopped the tumbler. The tumbler has been talked about in other posts.
The load included all the zebra cabochons, a selection of other small and medium sized cabs, water to just under the top of the load and 2 tablespoons of 80 grit silicone carbide.
The cabochons were then cleaned thoroughly and fire polished again, same schedule.
The result can be seen in the last photo.
Overall, I am happy with the whole process, though there are a number of things I would do differently.
Lessons
- See Part 1 for lessons about making the slab
- If staining or devitrification is visible would tumble first, before the first fire polish.
- Maybe not do. It was very time consuming.
Firing Schedule
Fire Polish – Bullseye COE 90 tumbled cabochons
Please be aware that all kilns fire differently and this schedule may not produce the same results in your kiln.
| Segment | Rate (C/hr) | Target (C) | Hold (mns) |
| 1. Strain Release | 222 | 537 | 10 |
| 2. Process | 333 | 732 | 20 |
| Crash Cool | Open Door | 560 | 0 |
| 3. Anneal | Full | 516 | 30 |
| 4. Cool | 83 | 371 | 1 |