Marcel, I love the work you do with opals. Here is another technique in case people are burning out their opals. Marcel's technique is probably faster. I just don't have the patience to work opals so gently and have burned out a few. I do the following technique and usually prep several at a time for later use.
When I incorporate opals into my work, I start with a tubing encasement first. I use small tubing, about 10mm. I cut a piece of tubing about 8 inches long, I heat one side closed, making sure to pull off any glass that may have scummed due to the cutting process. Then I basically have a small test tube shape. I drop the opal, or pour some crushed opal into it and make sure it goeas all the way to the bottom. Then I slowly heat the bottom of the test tube until it melts around the opal or crushed opal. If you want, after you get some of the bottom tubing melted, you can apply negative pressure to the inside of the test tube by sucking out some air etc, and the melted glass will collapse around the opal.
This method ensures the flame never accidently touches the opal or crushed opal frit. Once you get it encased, you can remove your gather from the end of the tubing. If you want, you can pull some of the glass off if you feel your encasement is too thick. You can add this encased opal to pendants, marbles, sculptural work etc and not have to work it so timid.
A couple points I want to add: When you are melting the glass around the opal, go slow so as not to trap any air on or near the opal. If you do the technique where you suck some of the air out, I would suggest you try it a few times with a piece of medium or large non opal frit so you know how much glass you have to melt first, how much heat you need etc. especially if you are not real familiar with working tubing.
Otter
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