agl junenewsletter2

8/14/2019 AGL JuneNewsletter2

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The Biggest Bang for your Buck.

2008

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D e f i n i n g Q u a l i t y f o r O v e r 3 0 Ye a r s

T h e K n o w l e d g e - Q u e s t R e p o r t o f C o l o r e d G e m s

Volume 1 / June 2008

NEW YORK, NY / 29 May 2008

Recently the American Gemological Laboratories (AGL) was sent a

number of faceted tanzanites that were discovered to have their color

augmented with a topical coating (figure 1). Although a number of

standard observations may reveal the presence of the coating,

advanced analytical testing provides proof.

Tanzanite has remained a very popular colored stone for retailers and

consumers. However, production for finely colored samples is not very

high, especially in smaller sizes. Our client first became suspicious of

these stones when he performed light repolishing and the color signifi

cantly decreased. indicated Christopher P. Smith, Vice President and

Chief Gemologist of AGL.

Although the face-up color of this coated tanzanite does not immedi-

ately make one suspicious, stated C.R. Cap Beesley, President of

AGL, careful examination of the stones with magnification revealed

tell-tale signs of a color coating treatment.

When viewed in the microscope over a diffused light source, particu-

larly in immersion, several of the samples revealed areas where the

Figure 1:These tanzanites were part of a group of stones

recently submitted to the American Gemological

Laboratory (AGL). It was discovered that their color

had been augmented by adding a very thin cobalt-

colored coating.

Stone sizes ranged from 0.29 to 4.22 ct.

Photograph by Fred Kahn & Sun Joo Chung

American Gemological Laboratories

Identifies -New Coating Treatment on Tanzanite

A e r i c a n G e m o l o g i c a l L a b o r a t o r i e s G e m R e p o r t

(Continued next page)


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American Gemological Laboratories Indentifies...

New Coating

Treatment

on Tanzanite

coating was incomplete. These areas occurred occa-

sionally on the flats of certain pavilion facets, but were

even more noticeable along facet junctions and at the

culet where the stone had become abraded

(figure.2a & b). In addition, with light reflecting off the

coated surfaces, a subtle iridescence was noted(figure.3a & b).

Utilizing advanced analytical instrumentation, AGL was

able to determine that the color of the coating was due

to cobalt. Cobalt is an element that is commonly used

to add a blue color to a variety of materials. according

to Beesley. Energy-dispersive X-ray fluorescence spec-

troscopy clearly revealed the presence of cobalt and

provides definitive proof of the treatment.

In the past, a Chelsea filter has proven useful to identify

cobalt coatings on other gem materials, such as sap-

phire. However, it does not provide a useful means ofidentification in this instance due to the fact that vana-

dium is the natural cause of color in tanzanite and it

also gives a red/pink Chelsea filter reaction.

Although all samples were positively identified with a

combination of careful observation, magnification,

immersion and a chemical analysis, one larger tanzanit

represented more of a challenge. All of the samples

were coated on the pavilion. However one sample

proved to be coated on only one side of the pavilion.

Smith stated (figure.4).This simply reinforces the need

to fully examine any gemstone over its entire surface.

Furthermore, a majority of the stones sent to AGL were

in calibrated sizes. The availability of smaller goods

with strong color is limited. indicated Beesley. So it is

not too surprising that such stones were selected for

this treatment. However, as they are small it is less like

ly that they will be sent to a lab for testing and so the

topic of proper identification and disclosure becomes an

issue.

Although topical coatings are one of the oldest known

treatment methods, recent developments in coating

technology have provided a resurgence in its applica-tion. We have seen a sharp increase in the types and

number of gemstones that are coated in the past sever-

al years. stated Smith. The quality of the coatings has

improved tremendously and it is now possible to mimic

virtually any color of gemstone. he concluded

Figure 2a & 2b:Topical coatings are

frequently identified when

the coatings are inhomo-

geneous, revealing spots

where the color is dimin-

ished, as well as along

areas where the coating

has been scratched or

abraded off. This was most

readily observed when the

stones were immersed

in a liquid, such as alcohol,

over a diffused light

source.

Figure 3a & 3b:Although subtle,

another indication of thecoating could be seen in

reflected light.

Under this condition,

the coating produced a

subtle iridescence.

The left image also

highlights tiny particles

of the coating seen

on the surface

of the pavilion.

Photomicrographs by

Christopher P. Smith

Figure 3a

Figure 2bFigure 2a

Figure 3b

(Continued from cover)


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About American Gemological Laboratories

Founded in 1977 by C. R. Cap Beesley, American

Gemological Laboratories (AGL), a subsidiary of the

publicly traded Collectors Universe (NASDAQ: CLCT),

pioneered the development of the worlds first compre-

hensive Colored Stone Grading System (www.aglgem-

lab.com).

AGL has also provided detailed country of origin andenhancement reports for some of the most prestigious

retailers and auction houses in the world for the past

three decades. In 2007, AGL was the designated official

North American laboratory of the International Colored

Gemstone Association (ICA). In addition, the laboratory

is the official colored gemstone laboratory of the 2007

Fine Jewelry CEO Summit and the JCK Las Vegas

Shows, as well as the 2007 Platinum Sponsor of the

ICA World Congress in Dubai.

About Collectors Universe

Collectors Universe, Inc. is a leading provider of value

added services to the high-value collectibles, diamond

and colored gemstone markets, with the Companys

common stock traded on the NASDAQ Global Market

under the symbol CLCT. For the most recent fiscal year,

CLCT authenticated and graded over 3 million items

valued at over $2 billion.

Contacts:

Cap Beesley Christopher P. Smith

[email protected] [email protected]

Figure 4Energy-dispersive X-ray

fluorescence spectroscopy

(ED-XRF) clearly identifies

the presence of cobalt in

the coating.

One larger stone however

presented a more challeng-

ing identification, as only

one side of the pavilion had

been coated.The red trace

was taken on the side of

the pavilion with no cobalt

identified, whereas the ligh

blue spectrum was taken

on the opposite side and

revealed clear evidence of

cobalt (Co).

The other elements of

calcium (Ca), vanadium (V),

zinc (Zn) and gallium (Ga)

are related to the host

tanzanite. This reinforces

the importance of testing

tanzanites in several

directions.

A m e r i c a n G e m o l o g i c a l L a b o r a t o r i e s G e m R e p o r

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