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 Post subject: Crystal Opals to back or not to back
PostPosted: Sat Jan 06, 2018 11:34 am 
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Hi, a little canvassing of opinion here.

Where you have obviously thin bits of opal you think are still very attractive, you can make a doublet out of them. Fine.

Where you have a crystal opal that is thicker, say 2-3 mm, that could stand on it's own, are you tempted to make a doublet with a black base to bring out the colour, leave it 'as is', or is there a third option of just colouring the back of the stone dark?

Doublets must be declared as such, which is as it should be.

What is the accepted norm in the industry of colouring the back of a stone? Again, it would be declared as such, but what does it do to the value of the stone?

A solid crystal opal, vibrant colours with a dark ink / pigment on the back or the same opal without the ink / pigment; how would you value such stones? A naturally dark crystal of the same vibrancy would likely be more expensive but if a transparent crystal could be offered with a black back, would that detract from the value of offering it with no black back.

I suppose what I'm asking is will you depreciate the value of the crystal opal if you make the back black rather than add a traditional doublet back?

Or would you leave the option of the coloured back to the stone setter?!

cheers,


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 Post subject: Re: Crystal Opals to back or not to back
PostPosted: Sat Jan 06, 2018 7:06 pm 
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Hi,

I saw your post on another Forum and have been giving it some thought. The name for the type of opal you're describing used to be "semi-crystal" not "crystal." Real crystal opal doesn't need backing to bring out its intense skin-to-skin play of color, though it may perform slightly better on a black background.

I know that opal terminology varies tremendously depending on who's using it. The new opal nomenclature adopted by the Australian Gemstone Industry Council lumps all transparent opal together as "crystal," which in itself is a misnomer because opal is amorphous, not crystalline. But traditional usage rules.

My personal opinion is that the first preference is to set such marginal opals in settings with darkened metal beneath them. But there's nothing wrong with cutting them as doublets if it's disclosed to customers when they're set in closed-back settings. Opals with low-intensity play of color probably don't have much more value than doublets made with the same opal, which should have more sales appeal.

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 Post subject: Re: Crystal Opals to back or not to back
PostPosted: Wed Jan 10, 2018 3:01 pm 
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Hi,

Your question I think could be rephrased as "what, in a general sort of way...." or "what, on average" ... is the value impact of doubleting a crystal opal with a permanent black base.

Thing is, opals tend to be so individualistic that an "average" or a "general sort of way" is a hard thing to ask for: each stone is different. There are however two general types of doubleting: one for blackening only, the other, as a salvage measure.

If I'm cutting a transparent or semi transparent opal of average normal thickness, in other words thick enough to stand on its own as a solid stone, I know that as a matter of course it will generally be anyway set in a blackened setting. Also I know my own blackening abilities better than I do the other guy's. So rather than leave it to the unknown next guy I do the blackening myself, usually by epoxying on a thin layer of basanite (ultra fine grained black basalt). The basanite is seldom more than 10% of the thickness of the stone, often much less, and is there only for colour. In a case like this there's no impact on what price I might ask for it except that the stone can no longer be sold by the carat. Of course the blackening gets disclosed and explained.

In the other case a layer of opal which would be too thin to yield a stone on its own can be sandwiched similarly to a backing material whether black or other colour to yield a composite stone thick enough to cut and strong enough to set. Here the backing works as a salvage, making useable something which otherwise would not be. As far as I am aware the general consensus is that a doublet of this type is worth +/- 10 percent of what a solid stone of equivalent size and colour would sell for.

Cheers,
Hans Durstling
Moncton Canada

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 Post subject: Re: Crystal Opals to back or not to back
PostPosted: Sun Jan 14, 2018 1:32 pm 
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Hi Rich and Hans,
Many thanks for your replies.

Rich, I wasn't too sure what you meant by 'Marginal Opals'. Not a term I've come across before.

Semi crystal and crystal as definitions are a little subjective I suppose.The stone below is fully transparent ...you're able to read text written behind it. The colour is present without a black background and yes it looks a little more eye-popping with a black base ...If it were shaped, it'd produce a stone about 3mm deep without any backing.

I've uploaded a couple of photos of the 'crystal opal' in question, both on black and plain wooden backgrounds (artificial lighting).

Hans, I hear what you say about the unknowns of 'the other guy's blackening abilities! I know what I can produce and I feel it would look nicer with a black back. Is there a call for such stones without black backs?
Regards,
Peter
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 Post subject: Re: Crystal Opals to back or not to back
PostPosted: Sun Jan 14, 2018 10:16 pm 
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Pusscat, "marginal" is not a technical term. I meant marginal as in less than intensely-colored crystal, i.e., many low play of color semi-crystal stones. You have to decide whether a backed stone, which always will sell at a small percentage of a solid stone price, will bring more than the same stone left unbacked.

In some cases the extra "pop" created by backing might make a low-intensity stone more saleable. It's a judgment you have to make. Each opal and each customer is unique; there's no rule book that covers all situations. I think darkening the metal beneath the stone is usually a better solution than backing; and as was suggested elsewhere, sometimes leaving the bottom of the stone lightly sanded instead of polished will enhance the face-up appearance.

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