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Appraising corundum


#1

my question to jewelry appraisers: how do you establish value for
corundum given that you are unable to determine whether or not its
color is the result of “bulk diffusion” aka beryllium diffusion?

best wishes,
bill


#2

Hello Bill,

Diffusion is easy to detect if the stone is loose, and can be
detected if the mounting is open in the back. There are also very
specific inclusions that are created after the diffusion process.
Gemology training is an absolute must to identify this and several
other treatments to gems.

If an appraiser is unsure if a gem is treated or unsure of which
treatment is present that appraiser should not perform the appraisal
and refer the client to someone who can.

Regards,
Jeff W. Nechka (G.G.)


#3

Contrary to some of the popular opinion, there are, in fact, some
very strong indicators available in many stones. A strong magnet, a
good scope, and an understanding of crystal chemistry is a great
help. As in many diagnostic situations, indicators are not proof,
though. But for most stones, the tell-tale signs are present,
especially the yellows and oranges, which are the most common.

Wayne


#4
But for most stones, the tell-tale signs are present, especially
the yellows and oranges, which are the most common. 

I am afraid but it is not that simple.

Yellow sapphires can acquire their color as a result of irradiation.
Natural yellow do have specific inclusions, but one must be familiar
with what they are. There are no tell-tale signs of heating in
irradiated yellow stones. Reaction to ultra-violet can be an
indication.

Some orange sapphires from Madagascar subjected to heat treatment at
much lower temperatures than from other locations and again heating
signs are not present.

In a funny way, the price is the best indication. A few hundred
dollars per carat, we can safely assume treatment. If more money are
involved, engaging a gem lab is a must.

Leonid Surpin
www.studioarete.com


#5

Leonid,

The original posting regarded berylium diffusion treated stones, not
just heated stones and there are fairly identifiable characteristics
of berylium diffusion treated stones. They were not talking about
irradiated stones or lightly heated stones.

Daniel R. Spirer, G.G.
www.spirerjewelers.com


#6
Diffusion is easy to detect if the stone is loose, and can be
detected if the mounting is open in the back. There are also very
specific inclusions that are created after the diffusion process. 

i believe that color concentrations observable when a stone is
immersed and color “bleeding” in fractures are diagnostic of
diffusion that is restricted to the surface of the stone, as with
titanium, but not to diffusion that penetrates throughout the stone
as is often the case with beryllium.

Contrary to some of the popular opinion, there are, in fact, some
very strong indicators available in many stones. 

it’s the stones that lack very strong indicators that concern me–it
seems logical to me that if some stones lack indicators detectable
with “small-lab” equipment (scope, liquids, etc.), then, in
principle, it’s not possible for small-lab gemologist/appraisers to
consistently separate “normal” thermal-enhancement from beryllium
diffusion treatment.

my understanding is that virtually all colors are being produced by
beryllium diffusion so how can an appraiser assign a value to ANY
corundum of ANY color when the stone may, in fact, be
"…artificially colored with beryllium"?

what i would really like is someone to say: "we have an inexpensive
protocol or instrument that separates all diffusion treated corundum
from thermally-enhanced corundum and this protocol/instrument is
available to those of us who don’t have the finances and expertise
of GIA or AGTA.

until such a protocol or instrument is in common usage, i have to
ask: how do you, as an appraiser, establish value for corundum,
given that you are unable to conclusively separate thermally-enhanced
corundum from beryllium diffused corundum?

thanks,
bill


#7
it's the stones that lack very strong indicators that concern
me--it seems logical to me that if some stones lack indicators
detectable with "small-lab" equipment (scope, liquids, etc.), then,
in principle, it's not possible for small-lab gemologist/appraisers
to consistently separate "normal" thermal-enhancement from
beryllium diffusion treatment. 

Well I just took a course at the AGTA Gem Labs in New York with
Richard Hughes on identifying corundum treatments (a class I highly
recommend to everyone) and they primarily use a microscope to
determine what’s being done to stones today. Not entirely, but it
seems to be an effective means of separation in most of the cases.
But your question about what appraisers should do is dependent on a
number of factors. Are you dealing with what may be a $10,000 stone,
or some 2 mm piece of material that it may not really matter as the
cutting costs make up more of the price? If you’re dealing with the
expensive stones and you can’t be absolutely certain then it pays to
send the stones to properly equipped gem labs. Your desire for an
easy solution is probably not going to happen for quite awhile. The
labs may end up being the ultimate arbiters in this and all stones
of value may have to be certed.

Daniel R. Spirer, G.G.
Daniel R. Spirer Jewelers, LLC
1780 Massachusetts Ave.
Cambrige, MA 02140
www.spirerjewelers.com


#8

Hi Bill,

Beryllium treated corundum is easily detected so called ‘deep
diffusion’ is actually not that deep and is easily identified with
color concentrations and specific inclusions. The stones lacking
obvious treatment are usually melee but at $1/stone…you seem to be
making a mountain out of a mole hill. Unfortunately there are too
many jewellers who think they are gemologists (due to ego,
supposedly experience, ignorance etc)…they should really take the
full gemology course before they talk and create panic in the
industry and decrease consumer confidence.

Regards,

Jeff W. Nechka (G.G., G.I.A)
Premier Gems LTD.


#9
The original posting regarded berylium diffusion treated stones,
not just heated stones and there are fairly identifiable
characteristics of berylium diffusion treated stones. 

I stand by my original post. Berylium diffusion treatment applied
differently, at different temperatures, depending on origin of the
rough.

So called “identifiable characteristics” are either not always
there, or not that obvious.

Leonid Surpin
www.studioarete.com


#10
Beryllium treated corundum is easily detected so called 'deep
diffusion' is actually not that deep and is easily identified with
color concentrations and specific inclusions. 

This is a misconception. Beryllium diffusion can go all the way
through the gemstone.

Leonid Surpin
www.studioarete.com


#11
Beryllium treated corundum is easily detected so called 'deep
diffusion' is actually not that deep and is easily identified with
color concentrations and specific inclusions. 

it’s my understanding that beryllium diffusion often penetrates the
entire stone.

i believe the people who brought this to the attention of the trade
are the big names at the labs–most of them have probably taken the
full gemology course.

Well I just took a course at the AGTA Gem Labs in New York with
Richard Hughes on identifying corundum treatments (a class I
highly recommend to everyone) and they primarily use a microscope
to determine what's being done to stones today. Not entirely, but
it seems to be an effective means of separation in most of the
cases. 

richard hughes has probably forgotten more about corundum than i’ll
ever know; if he’s teaching people to make the separation based on
visual examination, the problem can be dealt with. thanks, daniel,
that’s the answer i was looking for.

best wishes,
bill


#12

I went back and reviewed my notes from the AGTA course I took with
Richard Hughes and I’d like to correct some of my own statements.
Lattice-diffusion treatments in corundum are relatively easy to
detect with a microscope under the proper conditions. Beryllium
lattice-diffusion treatments are often detectable with a microscope
under the proper conditions but not always. To actually detect the
beryllium itself (not the heat treatment part, but the actual
presence of beryllium) often requires more sophisticated lab
equipment. So while it is possible to detect beryllium treatment with
a microscope, in many cases it is necessary for a gem lab to work up
the stone. My apologies to anyone I may have impacted with my
misstatement.

Of course, everyone needs to remember that with the speed in which
new treatments are being developed, everything we know to date could
be moot by the time a new batch of corundum appears in the
marketplace.

Daniel R. Spirer, G.G.
Daniel R. Spirer Jewelers, LLC
1780 Massachusetts Ave.
Cambridge, MA 02140
www.spirerjewelers.com


#13

Dan,

FWIW, every single piece of yellow or orangy beryllium treated
corundum I’ve seen responds to a strong rare earth magnet. No non-BE
treated or untreated one has, so far. And we’re dozens into it. May
be anecdotal, but…

Wayne Emery