Fused glass cabochons can get a scummy bottom from the fiber paper or shelf primer, and devitrification on the top. To clean these up, you can use wet and dry sandpaper or diamond pads, but an easy way is to tumble them with silicone carbide grit.
Thanks to Twylah for asking about this and inspiring me to make the video. Hope it answers all your questions.
The video tutorial includes the design, materials, and equipment information, as well as the cutting of glass, firing and slumping.
In the YouTube video, you will find links to related videos, a chapter list with time stamps, and links to more resources.
Don’t forget, the glass I use is Bullseye 90 COE. I use Thinfire fiber paper on the shelf, but when fire polishing on my shelf, and slumping in moulds, I spray with boron nitride mould release.
This is one of the easiest ways to clean up fused glass cabochons for fire polishing. It requires a single-barrel tumbling machine and some abrasive tumbling grit. A cheaper tumbler should be fine as you probably will only use it occasionally.
The tumbler I use is a Lortone but any single or multi barrel rock tumbler will do the job. I use 80 grit silicone carbide, but aluminum oxide will also work. Other grit sizes will also work, but I find the 80 grit works well for me.
When preparing the barrel, load it to between 1/2 and 2/3 full with a mix of cabochon sizes. I have a container of filler cabochons to use. These just make up the bulk if the job doesn’t have enough cabochons to fill the barrel.
By using a mix of sizes you ensure that the cabs get abraded over the entire surface. Small cabs get into areas the larger ones can’t.
Add about 2 tablespoons of the grit to the cabs, and then fill with enough water to fill just below the top of the cabs. Too much water will slow the abrasion. Too little will create too much harder abrasion and risk cracking the cabochons.
After about 2 hours check the cabochons to see how they are going. You will have variations as some colours, like black, do seem to abrade quicker. If they don’t have a nice matt finish, p[ut them back on for another hour or more. Just check again to see their progress. You want to process them just enough to get the finish you need.
Once finished, be sure to wash the cabochons thoroughly before the fire polish.
The silicone carbide grit can be reused so reclaim it, don’t throw it out. Remember, the water will contain fine particles of ground glass. Treat it with care. Don’t spill it around your studio without cleaning up. It will dry and leave behind fine ground glass which is a health hazard, as you should be aware.
If you have any questions please ask in the comments section on YouTube.