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Grams per carat - opals question


#1

Hi All, I’m writing in from my wife’s account (with her blessing)
hoping some of you out there can give me some assistance.

I’m interested in helping out my wife by selling off some of her
overstock of opals. None of them have been weighed per carat, but I
have an electronic scale that will do that part nicely.

My question is twofold:

  1. What is the standard conversion between grams to carats for
    opals?

and

  1. How do I factor in the ironstone backing on the doublets?

Many thanks,
Tom


#2

Opals are not usually sold per carat. They are usually sold per
piece. I have seen some white opal sold per carat but if what you
have is boulder opal, that material is always sold by the piece.

Daniel R. Spirer, GG
Spirer Somes Jewelers
1794 Massachusetts Ave
Cambridge, MA 02140
617-491-6000
@spirersomes
www.spirersomes.com


#3

Hi Tom!

1.  What is the standard conversion between grams to carats for
opals? 

There are five carats to the gram, regardless of the gemstone. To
get a reasonably accurate weight, you need a scale that will weigh in
1/100 of a gram. a 1/10 gram scale can only be converted to the
nearest 1/2 carat. For opals, this may be accurate enough
(“ballpark”) but for finer/smaller stones, you’d need greater
accuracy.

   2.  How do I factor in the ironstone backing on the doublets? 

If its an ironstone backing, its most likely a boulder opal or seam
opal. A doublet is constructed, and usually has a black backing
piece, such as onyx or basinite. If it is indeed a boulder opal, I
don’t think you need to factor in the matrix, or backing material.
Sell it as a boulder opal, by weight, and the buyer should
understand. Doublets and triplets are typically sold by calibrated
size, rather than carat weight.

Hope this helps!

Dave

Dave Sebaste
Sebaste Studio and
Carolina Artisans’ Gallery
Charlotte, NC (USA)
dave@sebaste.com


#4

Hi Tom,

There are five carats in a gram.

Doublets and triplets, (aways), and boulder opal (almost always -
only once have I ever seen it offered otherwise) are sold by the each
rather than by weight, precisely because it isn’t all gem material.

Cheers
Hans Durstling
Moncton, Canada


#5

If I my I’d like to add a qualifier to your opal comment. Fine opal
is typically sold by the carat. Opal in matrix most often is sold by
the piece. If the seller quotes carat price for matrix material look out.


#6

Tom, there is 0.2 grams per carat or 5 carats per gram.

On your second question, you don’t sell doublets or triplets by the
weight, just by the piece. There are too many variables in the
construction of doublets and triplets, including the weight of the
backings. Same goes for boulder opal. These stones sell by their
"wow" factor. A really nice stone will sell for much more than a
not so nice stone. A big really nice stone will sell for a bunch
more than a small really nice stone, up to a point. In other words,
it will sell for what the buyer is willing to pay and what you are
willing to accept.

Don at Campbell Gemstones.


#7

I agree that it doesn’t make sense to sell opal by weight. Would
you pay more for a 75 carat white opal with a little pin fire than
for a 25 carat black harlequin with lots of red? There are many
factors that affect the beauty and value of an opal that have
absolutely nothing to do weight.

  If it's an ironstone backing, it's most likely a boulder opal or
seam opal. A doublet is constructed, and usually has a black
backing piece, such as onyx or basinite. 

Not necessarily. It is quite common for opal doublets to be backed
with ironstone or “boulder.” And too many dealers get away with
calling these constructs “boulder opal doublets” which implies a
greater value than just “doublets.” I tried to make this point with
a dealer once at a gem show – that a doublet was a doublet, no
matter what it was backed with; he didn’t like that…at all! You
can usually tell an ironstone-backed opal from a natural boulder opal
pretty easily: The opal layer is usually perfectly even and there’s
a very thin black line (the adhesive) between the opal and the
ironstone.

Beth


#8
    I agree that it doesn't make sense to sell opal by weight. 
Would you pay more for a 75 carat white opal with a little pin fire
than for a 25 carat black harlequin with lots of red? There are many
factors that affect the beauty and value of an opal that have
absolutely nothing to do weight. 

Beth, White opal with a little pin fire sells for about $2-5 / ct.
Black harlequin w/lots of red sells for about $2000-5000 /ct. Thats
why opals are sold by the carat. There is quite a range opal prices
based on quality (soundness), brightness, color pattern, type (
crystal, semi-crystal, opaque), background color. See Paul Downing’s
book “Opal Identification and Value” for a good overview.

   It is quite common for opal doublets to be backed with ironstone
or "boulder."  And too many dealers get away with calling these
constructs "boulder opal doublets" which implies a greater value
than just "doublets."  I tried to make this point with a dealer once
at a gem show -- that a doublet was a doublet, no matter what it was
backed with; 

You are absolutely right - a doublet is a doublet is a doublet no
matter what it’s backed with and is sold by the piece (based on that
"wow" factor - thanks Don)

  You can usually tell an ironstone-backed opal from a natural
boulder opal pretty easily:  The opal layer is usually perfectly
even and there's a very thin black line (the adhesive) between the
opal and the ironstone. 

Some doublet makers are cutting the bottom of the opal wavy and using
epoxy filled with ground boulder for the bottom. It actually looks
pretty convincing. Beware! it’s still just a doublet.

Mark Thomas Ruby
SunSpirit Designs
Loveland, CO
970 669-7075


#9
   If I my I'd like to add a qualifier to your opal comment.  Fine
opal is typically sold by the carat.  Opal in matrix most often is
sold by the piece.  If the seller quotes carat price for matrix
material look out. 
Dear Orchidians,	 	For those of you that don't have much 

experience
buying opal, if you go to a trade show there will be dealers selling
any kind of opal, including boulder opal, solid and doublet by the
piece and by the carat. Any dealer who sells by the piece probably
bought it by the carat.

Rough is bought by the ounce or gram, after it is cut, what you

paid for it has to be divided by whats left in carats. Gluing the
piece to a backing does not change what you paid for the rough.

	 I would think that for convenience dealers price their better

stones before a show so they don’t have to weight and reweight the
same stone for different customers. Jayson Traurig(sp) is a vendor at
GLW shows and always has bags of doublets at $10, $15, $20 ect. per
carat.

	With opal, I have seen similar looking opal in different piles,

with very different prices. There is no logic sometimes to how it is
priced. Obviously the more intense the color, the higher the price,
and some colors are prized more than others, some patterns are
prized. Buying opal is a learning experience a little different than
other stones.

	 Solid opal or doublets can craze after you purchase them. Some

dealers will trade you out for stones that craze, even if you have
them for a long time. Other dealers don’t stand behind their
material. I lost $400 on a pair of earrings when one turned cloudy,
the company I bought it from doesn’t care after the sale. I can take
the good one and use it for some thing, but I have to pull the
doublet from the 14k gold bezel mounting, and I don’t know till I try
if it will survive removal, doublets can be chipped easily.

	Being an Opalholic, I have made a lot more good purchases than 

bad
ones over the years. Seems to be the price to be involved with
gemstones that are so beautiful and so fragile.

Richard in Denver


#10

Regarding Beth’s posting bout doublets having flat backs, I have
seen very irregular shaped opal doublets where they used something
brown, like glue putty between the curved back of the opal and the
stone backing that matched the color of the stone backing material so
it looked like a natural boulder opal. Sometimes I can tell that the
opal is an opalized clam shell. In my experience no dealers I have
dealt with try to pass off doublets as solid opals. Once they tell
me the price, if it seems to good to be true,I look carefully at what
I thought was a solid, I see the glue seam. If the stone is really
beautiful and it is reasonable in cost, and I can set it and sell
it, and the customer can wear it and enjoy it with the same care that
would be given to pearls, emeralds, aquamarines, ect.( things that
need more care), I don’t care that it is a doublet. Disclosure
applies, along with giving the customer an idea of what a similar
opal would cost if it was a solid, up to ten times the cost of a
doublet. We have sold a lot of opal over the last several years, and
our customers seem to take care of their opals as we don’t have
unhappy people coming back.

Richard in Denver


#11
 2.  How do I factor in the ironstone backing on the doublets? 
    If its an ironstone backing, its most likely a boulder opal or
seam opal. A doublet is constructed, and usually has a black
backing piece, such as onyx or basinite. 

Dave and All: there are many man-made “boulder” opal doublets on the
current market with ironstone backing. They are very well made and
can fool the unwary. In any case, doublet or natural, boulder opals
are professionally sold by the piece not by weight. The same is true
of any assembled opal, doublet or triplet. Opals are sold by carat
weight only when they are “naturals,” 100% opal.

Rick Martin
MARTIN DESIGNS