Step 8: Clean and polish
If you're lucky like me, you have access to an ultrasonic cleaner. If that's the case, put soap and water in that, throw your piece in, and let it vibrate for five minutes. Rinse and repeat for all pieces. Then replace your soap and water with a coarse polish, vibrate and repeat. And one more time with a fine polisher (I used an oil-based diamond slurry). That should get your glass looking lovely!
For flat sides, you can also try grinding with wet fine-grit sandpaper.
Our pieces, as you'll note from the pictures, have a distinct non-glass quality to them. Specifically, they're opaque.
We're not entirely sure what happened to cause this, but since our processing was rather messy, there are a number of possible points where this could have occurred:
-Melting could have introduced debris into the material. Our crucibles weren't perfectly clean, so little bits of dust and graphite got mixed in.
-Kiln casting occurred at a temperature higher than strictly necessary for slumping. We were trying to save time, but we might have introduced defects into our product.
-Devitrification could have occurred in our glass- crystals could have formed. Clear materials, such as glass and clear plastic, have amorphous microscopic structures, which means that they have no crystal structure. Sometimes, when glass is cast, it forms a milky, opaque surface, where the glass has crystallized around foreign particles.
The diamond slurry polishing should have removed any surface devitrification, but since the glass was mixed with foreign debris throughout in the melting step, this isn't enough evidence to cross off devitrification as a possible source of opacity. So I took samples of each type of cast glass to the SEM to look for crystal structure.
Two of the pictures above are through the SEM. They show the red glass at 60X and 500X magnifications. No clear crystal structure emerges, because the surface is too textured. The glass looks porous- there are hollows for many tiny bubbles within the glass.
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