Buckle in, this is a long one with a lot of prior research and a lot of potential questions 
So as the title suggests, I’m approaching a project as a newbie to not only rings but jewellery and any sort of metalwork beyond some basic lathe machining/welding/grinding altogether. The ‘design brief’ was “I want an opal engagement ring” a few years ago in passing, when it was far too early in the relationship for me to have paid attention 
Fast forward those years and I’ve been doing the slow burn research to make sure I’ve covered all bases, including a trip to Lightning Ridge to have a crack at finding an opal, and learning as much as possible from the source. During this trip I was made painfully aware that the softness of opal (5.5-6 on mohs) doesn’t make for a great everyday ring, but that’s not enough to deter me. I also learnt a lot about doublets and triplets on this trip, and it got me thinking about innovation/solution #1.
Problem #1 - Opal is soft.
Solution #1 - Cover Opal with something for protection.
I’m looking at this from a slightly different perspective to most doublets/triplets, in that the piece I have is a beautiful cabochon solid, and would absolutely not require any enhancement visually. I am aware that a typical doublet is about backing, not a cap, but as this gem needs no backing I am thinking of a non-traditional opal-and-cap doublet (call it a triplet with no backing if you’d like). Quartz is a common cap and would be OK if my more ambitious idea can’t come together, as it is a slight upgrade at 7 on mohs and would also be able to be replaced every X years without any sacrifice of the opal. The ambitious idea is Moissanite (9.5 on mohs). I have been reaching out to manufacturers that specialise in Moissanite and it’s looking like getting anything like a cabochon is going to be a challenge in itself. When one opal specialist I spoke to started talking through the doublet creation process, we stumbled across technical problem #2.
Problem #2 - Opal has a ‘coefficient of thermal expansion’, CTE ~= 6.44-7.38, and Moissanite is down at 4.0. For the opal specialist, this was enough of a difference to flag concern of delamination over time, and he explained that the difference in CTE from some glass (~9) to opal is one reason cheaper doublets and triplets fail.
Solution #2 - The adhesive used between the opal and cap should be flexible enough to compensate for the difference in CTE.
This problem/solution led me to speaking to adhesives specialists and manufacturers, in the hope that the specs I’ve now got would be able to be matched to a glue. Optically clear, flexible enough to survive many cycles of roughly 5*10^-6mm stretching, and unlikely to succumb to UV or other common adhesive failures. I have so far not had any luck, but I am nowhere near the end of the leads I have.
That’s the current mission for the gem, now for the actual ring! I know it will be a white gold alloy, I know the styles she likes and the design of the ring in CAD is something that IS in my wheelhouse (finally). My research has been clear that I should bezel set the opal for further protection and even pressure. I have dug into forum posts here and concluded that while it may be unnecessary, I like the idea of gluing the base of the opal to reduce risk of pressure points on the underside and to simplify the bezel setting. From a design perspective I am yet to settle on whether there will be other stones included; Separate from the opal I purchased while in Lightning ridge I did find some almost unusably small opal while fossicking that I like the idea of setting rough alongside the main piece.
In conclusion! I guess my post is asking for any insight people with more experience than me may have into any of the small but significant details I will come across in this process. For specific questions:
- Has anyone laminated/glued two substrates in their jewellery that have similar differences in thermal properties, and how has that gone?
- Any adhesive suggestions or leads on who to speak to?
- Any suggestions of jewellers in NSW, Aus who would be worth talking to/working with?
- Insight into the decision to include or not include extra stones/gems would be great!
- Any tips from a design perspective to make the lost wax/resin casting process as smooth as possible
- I’m interested in just about any input, even if for nothing other than a learning exercise! see below for caveat
And finally, input/considerations I’m not looking for 
- Suggestions of alternative stones. This is a “how do I make it work” project, not a “how can I work around it”.
- Suggestions of separate everyday ring and opal ring for special occasions. I want this ring to be a testament to the lengths I would go to for this woman to have the absolute best outcome possible. If any challenges become insurmountable, I can re-evaluate.
- I’ve heard plenty of cases of people looking after their opals and not needing any or much work to keep them looking nice, but I’m working on a best case scenario of something truly unique that ideally can be treated like any other everyday ring. If it all becomes impossible, I do know that I have many fall back options.
- I’m aware that delamination is a concern with any substrates and I’m not expecting to reduce the risk to zero, only to do everything I can to hedge my bets.
To those who made it to the end and intend on sharing some of their wisdom, thank you in advance!
