Glass and Opals
Glass is an ancient and fascinating material. Artificial production began at least 6000 years ago, but humans have used a naturally occurring form, obsidian, to make cutting tools for untold millennia. Made mostly of silica, the addition of other materials (namely metal oxides) can dramatically alter characteristics like color, heat resistance, or even tensile strength. I work with Borosilicate glass, otherwise known as Pyrex. The addition of boron trioxide makes it relatively resistant to thermal shock, ideal for baking pans or lab equipment.
Something about glass that particularly interests me is its compatibility with other materials. For example, synthetic opals can be encased in glass to create beautiful textures and sparkle.
One technique for encasing opals, which I demonstrated in an On The Torch video by Revere Glass, uses a combination of opal shards and crushed glass, known as frit.
To begin, I mixed crushed opals and clear frit. I recommend a ratio of about 1:4 starting out; if you want the sparkle to be denser, add more opal. I poured the mixture into a clear blank (a section of clear tubing attached to a narrower blowtube) and then slowly brought the glass up to working temperature in the flame, rotating evenly. As the glass heats up, the opal and frit mixture will begin to tag to the inside wall of the blank. The sparkle will only appear where this mixture sticks to the glass, so it is important to distribute evenly across the inner wall.
Opal has a curious property of floating in glass, necessitating a second layer of clear frit to ensure the shards are fully encased. Each layer has to be melted in slowly and carefully; the inclusion of small bubbles or non-melted frit can cause stress fractures.
To fully melt the frit, I gently inflated the blank via the blowtube and then rolled it on a flat piece of graphite known as a marver. Marvering helps keep the blank a cylinder for even heating. Stretching and reshaping the blank in this way helps ensure even heat and fuses the frit with the inner wall.
Once the opals are fully encased in clear glass, the blank can be used for any number of projects. However, I like the way opals look when backed with a darker color. It helps them stand out and sparkle even more. In the photo above I backed opals with a color containing various metals including silver, which gives it a ghostly blue sheen. For this demo I used black frit for a clean look that emphasizes the opal inclusions.
Multiple layers of black frit are needed for even coverage, and I followed the same steps to ensure even melting. Afterwards, I removed excess non-sparkly material and gave the blank its final shape.
The blank is still at working temperature in this shot, but you can see the opal shard reflecting green and blue even through the glow of the glass
