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Why did this opal fall apart?


#1

Recently finished a necklace with large rose cut Australian white opal, set in an 14k rose gold bezel. After the customer wore the necklace a few times – no collisions, no dancing, no falls, no direct hits to the stone-- large chunks fell out. See picture. Am trying to diagnose what caused this opal to lose chunks like this! Needless to say, this is heart braking and gut wrenching, as I am the designer and procured the stone which was then custom cut and set for the necklace. And I will need to make the necklace whole again with a new stone. Appreciate expert insights, thanks!


#2

opal is brittle, probably stress from setting the stone in a bezel in 14kt (which can be a hard alloy)

Mark Zirinsky
denver
gemcarver@pemed.com


#3

Get me off line at lshorowitz@yahoo.com We are miners-cutters of peruvian opals, gem silica, chrysocolla , etc Sounds like you have a water problem in opal possibly . Thank you
Lee Horowitz, M.Ed, CAGS, GemologistPeru Blue Opal Ltdwww.perublueopal.com


#4

I looked your pendant and thought it was an “accident waiting to happen”! Stress on a full-bezel setting is/was tremendous for this very soft stone!
I would have used four, double-claws to set that stone. Just my humble opinion

Gerry! from my mobile-phone!


#5

Was the bezel turned with pressure from a standard bezel tool? Perhaps the
pressure on the stone was excessive and only later affected it. Most of my
opal cutting education was from Paul Downing who recommended merely holding
the stone in place with prongs instead of rolling the bezel. He even
recommended putting a small drop of epoxy under the prong so that there was
not direct metal pressure on the stone. Such settings have taken a lot of
abuse while still protecting the stone.
Just my thoughts.
Fred Sias


#6

Though I agree about the possibility of excess pressure, I’m going with water problem… Some material (especially if you buy it “wet” will dry out and craze), you have multiple breaks indicating the stone was losing its moisture content and going into the crazing stage,
Are there any fracture/cleavage lines showing in the remainder of the stone?
My thoughts,
Jim


#7

I am so sorry that this happened to your lovely piece.
A good stable opal should’t have done this even while setting . We set
opals all the time often in reasonably heavy bezels and have never had this
happen. When ever I see an inexplicable stone break after it leaves the
shop it’s usually because the client is lying about dropping it or throwing
in a jewelry box up against harder stones like diamonds or corundum or
tossing it unprotected into a pocket or purse.
Have fun and make lots of jewelry.
-Jo Haemer
www.timothywgreen.com


#8

Fred- Gluing prongs to a stone is never an acceptable practice in the
trade. We never roll bezels we always use a setting punch and chasing
hammer. We often set opals in bezels that are 1or 1- 1/2 mm thick. Tim just
finished setting three triangle shape faceted Ethiopian Opals in platinum
with full bezels. No chips on the sharp pointy ends of the triangles
either. Frankly that setting job scared the shit out of me. I was afraid to
look.
Stone setting is really all about the seat, not the metal on top.
Have fun and make lots of jewelry.
-Jo Haemer
www.timothywgreen.com


#9

Have you ever looked closely at a a hand-chipped stone arrowhead? Those are
pressure flakes - originating at a point of excess pressure and flaking
conchoidially outward from there. With that in mind now look at the shape
of the flakes that came off the opal. Get the picture? What you have is an
engineering issue: excess pressure on the stone.This may have two causes.

One lies with the bezel. Bear in mind that opal is already a fragile sort
of stone. Thus you want to put the holding pressure on it gently, evenly
distributed all around, and in closing the bezel, “patting” the metal
against the stone like butter. This is easy with malleable metals like 22 K
or fine silver. But 14 K is resilient and springy and you have to force it.
This means the inside inside the bezel instead of being buttered up against
the stone all over, the metal may be in contact at only one or two or three
or some other number of individual points on the stone and with that you
have so many individual pressure concentrations that press against the opal
like pebbles under your bare foot.

The other cause may like with the shape of the cut opal. With opal, sharp
corners and flanks that are cut too thin are trouble waiting to happen -
again because they concentrate pressure into small areas.

Both these factors may work together. Hard metal plus thin stone? Give that
job to somebody else.

I might add that opal is about my favorite stone; I’ve cut a lot and set a
lot, so these observations come at first hand. There’s no other stone quite
as mysterious and magical and I believe it is for that reason that opal has
acquired such a baggage of myth and mystification - in a sort of unintended
compliment to the mysterious nature of the stone. For that reason it seems
to also draw the “mystificateurs” who pronounce, usually ex cathedra, stuff
like, oh you should never keep it in water, oh you should always keep in
water, never let it dry out, always let it dry out for at least six months,
always put it in glycerine, never put it in glycerine, etc. etc. It’s
hocus-pocus. Yours being an Australian opal water is about as likely to
affect it as are the gravity waves from Jupiter.

Cheers
Hans Durstling
Moncton Canada


#10

Hi Hans,

I thought the same thing, that they appear to be pressure fractures similar to flaking. But I don’t think they result from inward pressure from the bezel. Instead, those conchoidal fractures look like they radiate from the back of the cab, as if the base of the setting had some high points.

I haven’t worked with opal much, but I know it’s relatively fragile. If there were minor bumps on the base, could the downward pressure of the bezel be sufficient to induce flaking from the back?

-Alec

Just wanted to add one more thought as I look at the photo again, zoomed in… The origin of the fractures are inside the inner arc of the base. So maybe a more likely culprit than an imperfection on the base is something striking the back of the opal.

-A


#11

just looking at this now so if others have commented and said the same thing please forgive me

It has been my experience that with brittle stones (like opal) if the fit for the bezel is to tight before you solder it together, the solder bead will hold the stone up from the plate in areas causing a great deal of focused pressure on the bottom of the stone. When you push the bezel over that pressure increases significantly and will flake the stone off of the edge just like the pressure used to flake flint and obsidian to make a arrow head.

If you get away with setting a stone like this without it chipping even a small change in temperature (like coming in from a cold day into a warm house will cause enough thermal expansion to cause the stone to chip and flake.

we can not expect stone to have the same rate of thermal expansion and contraction that the alloys we use. And this is only one of many triggers that can cause this stone to fail under this pressure.

My solution to this is to

  1. make sure the metal is well annealed. After all pre-finishing just before polishing anneal the whole project carefully before polishing and setting the stone.
  2. inspect the bottom of the stone. if it has a sharp change and angle at the bottom take a fine diamond pad and give it a bit of a chamfer to soften that sharp edge. This will decrease the inward and downward pressure on that edge and help the stone seat better by keeping it away from any excess solder beading. When having custom cabs made or making them myself i make sure this is done.
  3. Make sure the stone slides through the bezel without binding on any part of it. after the bezel is welded down to the plate it will no longer flex and change shape. It will be locked into shape and might no longer be the same shape as the stone. If you have to force the stone into the bezel and have a difficult time getting it out again before turning the walls over the stone the bezel is not fitted correctly.
  4. the lower the k of gold the less dead blow the material is. If you are setting a fractious stone you are sometimes better off using richer material so you need less force to turn the bezel. Ever if a client has been quoted 14k there are times where you will save money and pain but using 18k for the bezel. There is spring back in most metals. This means when you push it over it has a tendency to spring back a bit. each time you hit it to push it over it gets closer but it also impacts the stone and work hardens the metal. Then more you need to push on that bezel the more you increase the chances of chipping and cleaving.

As a student this exact thing happened to me while making a set of moonstone cufflinks. It was heartbreaking to have them come back 2 weeks later with big chips off of the bottom and sides of the stones.

Les


#12

I suspect that it could be a combination of things. There may have been imperfections in the seat, although I suspect that effect would have been more immediate. It could be simply that the inherent tension of the setting process came into play as the stone was warned and cooled-- by the body and by the atmosphere. Jewelry is an art form that constantly moves through a variety of environments.
I also wonder if the facetting of a material like opal could have an effect. I am not a lapidary but I was working with tempered glass lenses this past summer, carving holes and removing material. They were fine until a critical mass was reached and the tension resolved. Crack, crack,crack…

Please excuse any typos-- curse my clumsy digits…


#13

When you say it’s a rose cut, I’m assuming that it’s faceted on the top with a flat back, sort of a thin, faceted cab. That’s what the photo looks like to me anyway. The issue that creates with opal (or any stone for that matter) is that the facet junctions create high spots that when bezel set will create pressure points that result in uneven pressure applied all around the stone. I’m also assuming that if it’s cut similar to a rose cut diamond, it has a very thin, sharp girdle. This adds to the fragility around the edge of the stone. Now take that very fragile-edged stone and set it in a full bezel in a relatively flexible piece, give it a tiny twist or flex and you’ll get exactly what the photos shows. Two fractured areas, pretty much opposite each other. It would take very little pressure to break that stone, even as little as setting it down on a hard counter top in a slightly less than gentle manner. A rapid temperature change might even be enough to cause flexing sufficient to break it.

The solution is to have your cutter leave it a little thicker on the girdle, rounded a little on the back. Basically, you want a more rounded cab shape. A thicker, rounded girdle is far more resistant to cleaving when pressure is applied unevenly to the stone.

I think I would recommend having a cutter with more intimate knowledge of both opal and bezel setting do the cutting for you. Someone that knows their stuff should have been watching out for you a little better on that one.

Dave Phelps


#14

Thanks, everyone…this is infinitely helpful and now I know what to do with the next opal!


#15

During my apprenticeship I dealt with a lot of Australian Opal. I was taught that all settings need to be a good fit maybe a cigarette paper thickness gap all around. Never to have it too tight. Don’t use glue.
Most white opals look better on a black background (brings out the colours better) so we used to have fully enclose back with a thin piece of black cardboard under stone. The cardboard also gave a little padding for stone. The back needs to be completely level with the stone. Don’t have the bezel too thick. Opals can take a fair amount of pressure but not too much. But if they have any flaws then they take very little pressure.
You may need to check if the customer perhaps has an ultrasonic as opals cannot handle one.
However when doing my apprenticeship there weren’t any faceted opals. My guess would be that a faceted opal may not be able to have a bezel setting as it may have more pressure on the points than it can handle.
Just a thought, if the customer wants bezel set you could possibly scallop the bezel to only be set on the flats of the facet and not the points but you may need to try it on a cheap stone first to see how it looks. Good luck!
From a fellow jeweller down under.
Monique
Australia


#16

I also feel that you should have burred an edge inside for the Opal to sit into, this would have relieved the pressure slightly


#17

…a softer metal 22ct bezel with attention to the under bezel {your seat} also czek the leading edge of the underside , if it is sharp slightly {diamond file or emery} to round it off slightly, as the pressure is brought to bear evenly over the stone. I have found that, often opals are sharp at the base edge, due to the polishing process. This is why it has cracked in this way , the stone has a memory & will chip some time after setting , as sympathetic vibration awakens the memory of uneven pressure. Sorry that you have had this problem , there are plenty of helpful thoughts here & that’s a good thing ! as you are now for-armed ,> Interesting to note, the old saying “Opals are bad luck” this was started by Jewelers {I believe} because of the Opal’s very brittle nature ! , Bestos Marcos.


#18

Yes, the bezel may be the culprit…need to think about ‘holding the opal’ rather than ‘capturing the opal’ . I have had exactly the same looking issue with an opal ring…the lady had been slapping her hand upon a table top when zap, a chip under a prong…opal, turquoise, amber and other soft stones are subject to damage from rough treatment or hard mounting…a little layer of cork in the bezel or glue under the prongs sometimes helps to release pressure on the stone…let the glue dry before mounting the stone as the fresh glue adhering to the opal may ‘trap’ the stone and create other issues… have a fine and creative day


#19

|
| | andy_c
January 20 |

|
| I suspect that it could be a combination of things. There may have been imperfections in the seat, although I suspect that effect would have been more immediate. It could be simply that the inherent tension of the setting process came into play as the stone was warned and cooled-- by the body and by the atmosphere. Jewelry is an art form that constantly moves through a variety of environments.
I also wonder if the facetting of a material like opal could have an effect. I am not a lapidary but I was working with tempered glass lenses this past summer, carving holes and removing material. They were fine until a critical mass was reached and the tension resolved. Crack, crack,crack… Please excuse any typos-- curse my clumsy digits… |

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#20

As a gem cutter I do not particularly like to facet any opal but when I have to I make sure the girdle is thick enough to take the pressure of the setting process.

With your design I would strongly recommend you to check that the girdle is not only thick enough but also has a bit of an angle just above it. I am not sure how to explain it properly but looking at the stone side on your base is flat, the girdle is at a 90 degree angle & then you would have another smaller “half girdle” at 45 degrees between the girdle and your first level of facets. That way you have a smoother, more even surface to set your opal in the bezel. That will also remove the potential “pointy” bits from the faceting where it could cause issue when setting. For added safety you can also have another 45 degree half girdle for the base, makes it a little less likely to chip if there is a little solder left at the base of the setting…