Opal Tips and Tricks
These "Tips and Tricks" have been developed over 15 years and should help you achieve a high success rate with your encasements.
We strongly suggest that all opal prep be done before one plans to use the stones in a more involved project. This will allow you to separate any stones that seem troublesome from the start. It also will allow you to troubleshoot your tech as there are many less variables to consider in the prep process then in a full piece.
We strongly suggest that you use quality clear boro glass, we prefer Simax but that's just us.
Always keep the heat down. Use as little heat as possible and take your time. More complicated stones can take 30 min to encase. Too much heat will boil your opal.
Both when working your opal and with your completed project you always want to have 2 to 3 times as much glass around the opal as the opal is thick. Large stones, like coins, require muth more glass, perhaps a minimum of a cm of glass around all parts of the opal. Just keep in mind that the opal is trying to break the glass and you need enough glass around it to hold it together.
If you skin an opal (stripping away most of the glass) you have to keep it out of the direct flame as best you can. The glass protects the opal and the opal will quickly boil in the direct flame with very little glass around it.
A skinned opal will most likely not survive the annealing process so be sure to add more glass to a skinned opal before finishing your project.
Before putting the encased opal in the oven, warm the encased opal to a constant temp throughout.
Opals don't like going through multiple annealing cycles (perhaps more then 5 or 6)
Opals don't like to stay above boro melting temperature for very long. Try to keep the opal from going above and below melting temp a bunch of times.
Try incorporating the opal into your project towards the end to increase your success rate.
Rough opals should have a 60-70% success rate, Tumbled opal: 8O+%, Cabochons 6mm or smaller: 90%+. Spheres are probably the most successful because they are 100% polished and have no hard edges.
Opal encasement process: This is for opals without voids or toothed edges.
Take a clean heavy wall tube, commensurate with the size of the opal, and.seal one end. Be sure the tube is free of glass bits created by snapping the tube to the correct length.
Slide the opal down the tube
Using a very small center fire. Heat the very bottom of the tube until the opal just barely tacks to the bottom — the smaller the tack the better. This prevents the opal from rattling around during warm up.
Once tacked, warm the tube up using a flame annealing tech. You will see the un-encased opal glow slightly.
Once the opal and glass are about the same temp, begin collapsing the tube around the opal starting at the bottom, where the opal was tacked.
Once encased, punty off and warm the entire gather to the same temp, and place in a kiln at garage temp
To anneal, ramp the kiln to 1075-1100 and then cycle down, or crash the kiln if analog.
This last step is critical — do not open the kiln until the next day when the kiln is cold to the touch. The encased opal should be cold all the way through and may require extra cool down time for large pieces.