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Author Topic: Opal Doublets, Natural Doublets, Opal Inlay what’s it all about  (Read 213 times)

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Opal Mike

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Hi all again,

As we bunker down in the middle of this awful carona virus, I thought I might take this opportunity to slightly further the interesting thread around doublets. My workshop

I think you guys nailed the definition of a doublet in the earlier thread, but there was a little blurring around ‘blackening agents’ and inlay.

Doublets as already established are a composite of two layers, the opal layer and a backing. The most common backing (commercially cut) is ironstone (boulder opal host rock). The opal is glued to the ironstone usually with two pack glues with a blackening agent added (the Asians use nigresene powder). Other smaller niche cutters, which I now call myself after years of being one of the true bad guys (full blown mass production), use Lightning Ridge black potch, is or black obsidian (as I do).  These last 2 don’t require the use of any blackening agent, although the Lightning Ridge cutters still seem to insist on using a blackening agent.....for the life of me I don’t know why...totally unnecessary and detracts from the bond integrity.

Before I go into inlay, I want to talk a bit more about doublets.

If you have read through the previous doublet thread and pics posted there, you will see I make a fair bit of noise about the thickness or thinness of the opal layer and I talk about opal content.

Technically any thickness of opal can be called a doublet so long as the opal layer on top is the polished part and the face of the stone...(no glass cap).  If you troll sites like the opal auctions site, you will find hundreds of thousands of commercial doublets ...pretty cheap. These are all cut in China, backed with ironstone with a very thin veneer of opal. They are flat on top and all contain a blackening agent.

These doublets are prone to chipping and breaking when setting into bezels, which is why 90% of doublet jewellery you see on Etsy or eBay sees the stones glued in...not properly set. Even the sellers selling Lightning Ridge Black solids set stones this way...not always to be fair, but it is pretty common and easy to pick if you look closely.

Then there are doublets cut with thicker opal layers, using better backings as referenced above. Generally, they are far superior, depending on the process and the cutter.

I use obsidian as I have stated and shown in the other thread. I have tried everything over the years including manufacturing several hundred thousand ironstone backed doublets. Nowadays I only cut my own opal, and I use obsidian exclusively...this is why.

I have referenced several reasons in the other thread...won’t repeat what I said so go read that if you are interested. Apart from that though I will go further here.

Obsidian as we know is a naturally occurring volcanic black glass. I use black obsidian. I like it because I can get a variety of translucency as discussed in the previous thread, from fully opaque sliced at 2mm to a lighter more translucent look that allows much more light through the finished stone, and still looks dark. Obsidian gives the finished stone a completely natural look and brings the opal to life adding depth and light to the stone. The finished look in jewellery is stunning..I will post a couple of pics later to show you.

That brings me to the term inlay, infill, and blackening of opal and jewellery settings, and for what it’s worth my opinions on all.

Firstly let’s talk about inlay. Opal inlay continues to be popular despite most of it now being made from synthetic blue green opal. There are still some people that make opal inlay jewellery with a variety of success and quality. Without disparaging the work of the very few fine artisans that make stunning pieces which I will get to in a minute, the vast majority of inlay jewellery is a disaster just waiting to happen. It is just not a good idea to lap opal down to inlay thickness which is generally thinner than 1mm and glue it straight into metal inlay settings with a blackening agent behind the opal and sitting in the setting. Nearly all inlay has squared sides and sharp corners...again a disaster waiting to happen, especially in rings that have a habit of getting hit into hard objects occasionally.

There are some exceptions. Some of the old school highly skilled inlay artisans will curve the inlay slice (use round wheels on fixed arbors) to match the curve of the opal with the curve of the ring setting. These guys know who they are and my hat has remained off to you guys...and one very clever gal whom I won’t embarrass on here. These guys are true artisans, and make very fine quality pieces, and they get a lot of money for their pieces (because they use much thicker opal and spend much more time making the inlay more secure ...plus their obvious dedication to quality).

When you see the term inlay, it generally means the opal has no backing apart from a blackening agent, or black epoxy between the stone and the setting (absolute disaster in my book). Some opal people will use the term ‘inlaid opal’ in jewellery. This often can mean that they have used a doublet, and have glued it into a bezel setting. I don’t really understand why they call it that, perhaps they perceive the term inlaid is held in higher regard to the word doublet.

We occasionally will make a piece of jewellery that is in essence a form of inlay, or at least designed to have that streamlined look. What I do, is back the opal onto obsidian as per a normal doublet, and I take the backing down pretty thin, generally about 1 to 1.5mm depending on the thickness of the opal layer. I like the completed thickness to be around 2 mm minimum...which is twice as thick as the average inlay at least.

We ( I really mean Jenni ...she is the clever jeweller not me...and I cut them as per instructions), seat down the settings to as close to flush as possible. We can’t fully replicate the inlay look as Jenni has always insisted on setting even small rings like this into proper bezels, meaning that the stone/s are properly set and will not chip or break.

We manage to set some reasonably sharp shaped stones such as squares or cornered stones using this technique. The stones are proper doublets, and are carefully cut to ever so slightly soften the edges and the corners. They look sharp, but they feel nice and soft in the fingers if you pinch them. With a bezel around them they are good to go, and will last the distance.

Some of you are probably wondering why I would bother to go this effort.

I am sad to say that there are a lot of miners and very poor cutters in Australia passing themselves off to you guys and the world consumer, as self professed opal experts and professional cutters.

We have spent most of our lives building our knowledge and experience the hard way. We lived for 20 years In Coober Pedy, and we have quietly been mainstream wholesale supplies for many years. Jenni did her jewellery apprenticeship over 4 years and required us to travel 7 times a year by car with our young family driving through the desert to Adelaide a trip of over 850km each way. We had to rent a flat, and stay for a week each time, so Jenni could complete the academic side and pass her technical tests to become a fully qualified jeweller. She is a gifted jeweller and won the South Australian apprentice of the year award in her final completing year.

It drives us nuts when we see dodgy, poorly cut stones, and even worse jewellery, especially coming from self pronounced opal experts from Australia.

I can tell you guys (Americans), I have spent a lot of time in the US, and have given a lot of my time guest lecturing to final year university students studying jewellery, to help them gain confidence and understanding about using opal.

I have been in more jewellery workshops in the US than I can count, and am always thrilled and encouraged by the American artisans, especially the lapidary guys out there. From my experience the American cutters are far more knowledgable and much better skilled than just about all of the opal people here in Australia!

I am really passionate about opal, opal jewellery and in particular the merits of well made opal doublets.

For my money, they are sensational value, and are an absolute premium product if cut right....

I guarantee all my doublets for life against lifting (delaminatiin). They are water resistant rated to 1000hours of continuous immersion ( meaning the glue doesn’t even start to break down until that point. I can soak them in metho for cleaning...doesn’t touch them, and they are completely safe in the ultra sonic.

Thanks for reading, and I hope that I might continue to help everyone improve their opal outcomes and further their addiction!

I will include a couple of pics of Jenni’s recent doublet jewellery...and one green orange solid ring.

Mike
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Opal Mike

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Re: Opal Doublets, Natural Doublets, Opal Inlay what’s it all about
« Reply #1 on: March 26, 2020, 12:04:24 AM »

This one shows what I mean about slightly softening the corners and bezel setting. The stone shape still looks sharp, but it won’t chip or break when leaning on it to set the stone.  We never ...repeat never glue stones into settings. If you guys want to make jewellery and work with opal...learn how to make bezels and practice setting stones..

That way your opal jewellery becomes heir loom quality...instead of temporary costume jewellery just waiting to be chipped or cracked or broken completely (stone).

I will go away now and leave you guys in peace.

Mike
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latte

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Re: Opal Doublets, Natural Doublets, Opal Inlay what’s it all about
« Reply #2 on: March 26, 2020, 04:56:29 AM »

Thank you for your incredible post that shows us what to shoot for.
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Felicia

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Re: Opal Doublets, Natural Doublets, Opal Inlay what’s it all about
« Reply #3 on: March 26, 2020, 02:18:12 PM »

Good posts. Learning this stuff is great. Thanks
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vitzitziltecpatl

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Re: Opal Doublets, Natural Doublets, Opal Inlay what’s it all about
« Reply #4 on: March 27, 2020, 06:15:58 AM »

Soooo much good info in these threads.

Re blackening agents, you posted that "...cutters still seem to insist on using a blackening agent.....for the life of me I don’t know why...totally unnecessary and detracts from the bond integrity."

A goldsmith/jeweler friend of mine who cuts always used "lamp black" to color epoxy. He would also use finely ground boulder matrix if using ironstone for the back of a doublet. Those particulate type additives would obviously reduce bonding capacity. I've wondered how much the liquid coloring agents reduce the bond strength.

The tip about moving the stone/backing back and forth to remove bubbles and make the join line thinner is great. Doesn't take very much epoxy to hold them together if you use good products, right?

Thanks again for these posts and photos.

Opal Mike

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Re: Opal Doublets, Natural Doublets, Opal Inlay what’s it all about
« Reply #5 on: March 27, 2020, 04:53:37 PM »

This is an interesting dilemma Vince, the ground ironstone (boulder), used as backing. This is used a lot to fill the back of curved pieces of thin opal, in particular ‘skin shells’, opalised pieces of shell. Without using this method these pieces get wasted, unless they are large enough or thick enough to be lapped flat (curved bottom), which leads to a lot of loss in size best case scenario, or total loss of the piece....hence the dilemma.

Most Aussie and Asian cutters historically use the crushed boulder method, mixing with glue and nigresene or similar blackening powder. Black epoxy or resin is also used.

So why don’t I use it?

From a wholesale perspective, I can’t afford my customers to have bad experiences with stones; stones cracking, breaking, chipping etc during setting, and worse some time later after the piece is either sitting in a customers jewellery cabinet or being returned by a disgruntled customer.

I experimented with the crushed boulder method early on cutting several hundred skin shells. I kept them in the safe for 2 years and found that pretty close to half had cracked.

I decided to just keep the rest and not sell them.

Last year I visited a friend of mine, Stuart Jackson, whom I worked with at the Coober Pedy TAFE Campus assisting with the development of the national Opal Industries Course.

We discussed this very topic at length and Stuart gave some interesting insights.

Over many years , Stuart has tapped more broadly into the commercial cutters around Australia than I have. He confirmed that my 50% crack rate is bang on what other cutters have reported to him over many years, in relation to crushed ironstone and blackened glue.

This extends to using resins etc to fill the curved backs.

I have a theory on this that extends to using flattened, blackened ironstone on conventional doublets, and is another reason I like obsidian.

Firstly skin shells; they are thin, and vary in thickness, meaning weaker and stronger points. Being curved makes it that much harder to achieve an even backing support, if that makes sense.

Then there is the difference in hardness and surface tensions between the ironstone, glue and opal.

I think I mentioned before that my crack rate is under 1% using obsidian and ultra violet glue. This isn’t achievable using ironstone, which will see a crack rate of up to 5% on traditional doublets.

I have already talked about why I like obsidian, and Lightnig Ridge black potch for that matter for backing. I will add to that in another way. Obsidian is very similar to opal. Similar in hardness as well. I like that when it comes to bonding the two. I believe that the similar hardness allows them to bond in harmony, as opposed to the filled crushed boulder method which sees different contraction rates and pressures that can lead to big cracks, a give away that there are opposing stresses.

In terms of glueing stones together, I think I have the runs on the board.

My bread and butter which I haven’t talked about was my triplet production workshop. My workshops have produced almost 6 million triplets over 30 years, and none of them have ever lifted.

I designed my UV gluing system years ago, and have used every other glue out there on opal and other stone. I glue all my doublets using this method, with the light source setting the glue off through the top of the opal...even pretty thick opal.

Other cutters use two pack glues which are fine in small numbers, but don’t offer the water resistance or solvent resistance. The bond strength is pretty good using UHU, probably as good as the UV. Just how much the bond strength is diminished using blackening powders is uncertain, but it must be a factor.

So back to the dilemma, to fill or not to fill. That is up to you. Just be prepared that the stone may crack...it also may not! If you are cutting these pieces for yourself, does it matter?. The alternative is that you either get a much small piece to work with after flattening the curve and shrinking the face, or you can’t use the piece at all.

For me it all depends on whether you plan to sell it or keep it for your collection.

Part of me likes the idea of not wasting nice colour...giving it a chance, but coming from the commercial food chain, I could not afford this option.

I have included a few pics of my light boxes for the UV glue. Nothing high tech apart from them being spot on in terms of distance from light source etc. Easy to make.

Mike
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vitzitziltecpatl

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Re: Opal Doublets, Natural Doublets, Opal Inlay what’s it all about
« Reply #6 on: March 27, 2020, 07:35:22 PM »

Nice setup on the UV box. That would cure a lot of them at once for sure.

My jeweler friend liked to use the crushed ironstone or lamp black just to make the epoxy line less obvious. If he had worked the join line down the way you described to make it really thin it wouldn't have been an issue.

Different expansion/contraction rates are definitely an important thing to consider. Maybe more so than anything else, eh?
 
True black Ridge potch is a sore point for me. I'd been watching an auction for a huge piece, but forgot about it and it ended without me ever putting in a bid. That was years ago, and I haven't seen another piece like it since. We have some smaller bits here, and don't use all that much, but it would've been nice to have that one.

Jhon P

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Re: Opal Doublets, Natural Doublets, Opal Inlay what’s it all about
« Reply #7 on: March 28, 2020, 02:08:25 PM »

 Great read mike. Thanks
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irockhound

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Re: Opal Doublets, Natural Doublets, Opal Inlay what’s it all about
« Reply #8 on: March 28, 2020, 07:15:15 PM »

Mike, I have looked thru the post and couldn't see the UV glue that you use.  I am wondering if it might be a better idea for some doublets and triplets I am going to do.  I recently got a huge amount of Spencer Opal with some that will cut solid and don't need it but some good doublet thickness material and a lot of triplet thickness.  Problem I have encountered is mixed results in air bubbles even trying the heating of the 330 to try and remove pockets.  I have had successes but just not willing to go thru all the trouble of getting the material perfect and then possibly having it go south with some air bubbles showing up.  normally when they do it is from an edge so I think the bond isn't great and water causes the edge to fail, not sure.  The material I got has some that the gentleman had made and also show this problem.  I guess the other question is where do you sit on how fine do you take the material to before bonding.  Some people suggest lower grits so the "bond has something to grab onto" and I feel that it also at low grits causes a distortion and may give it a more cloudy appearance.  Others say 600 grit and no more or it will be too polished and easier for the bond to fail.
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Opal Mike

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Re: Opal Doublets, Natural Doublets, Opal Inlay what’s it all about
« Reply #9 on: March 28, 2020, 08:41:02 PM »

G’day Steve,

Yeah look, the thicker two pack glues are certainly trickier in terms of bubble removal. Warming things up does make it a bit easier but bubbles still make things ah interesting. This is the main reason why blackening agents are used by Lightning Ridge doublet cutters when they use black potch...because the bubbles can be seen through the opal.

I don’t like bubbles...period which is again why I use UV glue and obsidian. With this technique I glue cold, in my case inside a commercial fume cabinet, ( because I do so many).

You raised an interesting question about lapping the surfaces.. short answer is a little courser doesn’t hurt for epoxy based glues and thicker glues, but the opposite for UV. For maximum bonding strength get both surfaces nice and smooth...a nice fine 600 sintered lap finish is fine enough.

Another advantage with UV glue is that it will fill any pits or scratches in either surface.

If you want to give the UV a crack, you will need non filtered UV tubes. I will post the exact tubes tomorrow when I return to my workshop.

Just make a smaller sized box and line the top with some thick foil sheeting to improve the light refraction...don’t really need it but it works for me so why not.

The UV glue is UV loctite 363. You can buy it in 50ml bottles...it is expensive. I have to import it from the US and I buy it in 1 lt bottles...but I know they supply it in 50ml yellow bottles.

When you use it use surgical gloves, and work in ventilation...put a fan on and open a window if possible. If you are only doing a few here and there no problems.

I won’t go into detain now as to method...but when and if you go down the UV road just ask me again..it is pretty simple for doublets, a fair bit trickier for triplets.

Mike
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irockhound

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Re: Opal Doublets, Natural Doublets, Opal Inlay what’s it all about
« Reply #10 on: March 28, 2020, 10:27:01 PM »

Awesome, thanks for the info Mike!
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vitzitziltecpatl

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Re: Opal Doublets, Natural Doublets, Opal Inlay what’s it all about
« Reply #11 on: March 29, 2020, 07:32:40 AM »

Yeah - thanks for the product info!
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