Gemnotes 16-05-10

Preface to the first

GEMNOTES Vol.1, No2, May 2010

!Important Pearl Laboratory Alert!

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GEMNOTES, Vol. 1, No. 2

Preface to the Second Edition of GEMNOTES

The year 2010 has started quite turbulent with lots of difficult issues. Currently much is being done at the lab for diamond and pearl research, but also on all the other hot issues such as ruby, sapphire and various treatments and synthetics. The diamond research includes irradiation and HPHT issues, the pearl research unsolved issues such as Keshi etc. While much time has been invested in these difficult and important issues new instruments were acquired and developed at the laboratory. So the laboratory keeps on moving and developing strongly. The new Gemmoscience group is also progressing, and the members of the group are in constant exchange of information and samples for analysis. There are several publications about to be published on various interesting topics with several of the members of Gemmoscience involved. This issue of GEMNOTES is mainly concentrated on a new type of cultured pearl that has recently appeared in the market and that is extremely difficult to be unambiguously identified Table of Contents GEMLAB Laboratory News May 2010....................................................................... Page 3 Important Note Concerning Pearl Reports............................................ Page 3 New Instruments at the Lab............................................................... Page 3 The GEMMOSCIENCE Group.................................................................................. Page 4 GEMNOTES Important Pearl Laboratory Alert........................................................... Page 5 - 11 GEMNOTES Short Papers...................................................................................... Page 12 Irradiated Diamond with Umbrella Effect.............................................. Page 13 - 14

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GEMLAB Laboratory News May 2010

Important Note Concerning Pearl Reports

The current situation in the pearl market (see page 5 – 11) has led us to decide that for the time being, at least until mid-June, we at the GEMLAB laboratory will stop issuing reports for Pinctada pearls, except for evident cases such as pearls in ancient jewelry pieces of known provenance. New Instruments at the Laboratory The first 5 months of 2010 we have continued improving the analytical capacities of the laboratory. While the analytical capacities of the photoluminescence system were strongly enhanced by the addition of focalizing optics and better quality filters and the UV-Vis-NIR spectrometer was equipped completely by Spectralon, several new instruments were acquired and developed. The new instruments acquired and developed in 2010 include:

High sensitivity and high resolution Photoluminescence spectrometer system using a 405 nm laser and a new thermoelectrically cooled double channel front illuminated CCD spectrometer

New Varian FTIR spectrometer for improved FTIR capacities

New controlling unit for the radiography system We custom build the Gemlab UV-Vis-NIR spectrometer system for interested laboratories and gemmologists, with various configurations (wavelength range, resolution, sensitivity), capable of low temperature spectroscopy, and to capture polarized spectra plus reflectance spectra (accessories upon request). The system permits to take low temperature spectra of diamonds as small as 1 mm. Standard configuration: range 240 to 1050 nm, resolution approx. 0.75 nm, 15 cm integration sphere.

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The GEMMOSCIENCE Group The website of the GEMMOSCIENCE Group is now online and can be found under www.gemmoscience.org. Some parts are still under construction but should be finished by latest end of May 2010. And here we present: the GEMMOSCIENCE logo!

The GEMMOSCIENCE Group consists of the following persons/laboratories: Franck Notari, GemTechLab Laboratory (Geneva, Switzerland), FOUNDING MEMBER Thomas Hainschwang, GEMLAB Laboratory (Balzers, Liechtenstein), FOUNDING MEMBER Prof. Dr. Emmanuel Fritsch, Institut des Matériaux Jean Rouxel (IMN-CNRS) (France), Dr. Benjamin Rondeau, Laboratoire de Planétologie et Géodynamique, University of Nantes (France) Dr. Laurent Massi, AIGS (Asian Institute of Gemological Sciences) Labor (Bangkok, Thailand) Dr. Bertrand Devouard, Department of Geosciences, Blaise Pascal University, Clermont-Ferrand (France)

Multidisciplinary Scientific Group for Gemmological Research

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GEMNOTES

Urgent GEMLAB Laboratory Alert

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A Difficult New Type of Cultured Pearl Entering the Market By Thomas Hainschwang Natural pearls have had a steep rise in popularity and consequently quantity in the past years. Uncommon quantities of allegedly natural Pinctada pearls are currently available, of which a good percentage are Keshis (beadless cultured saltwater pearls). The identification characteristics of Keshi pearls were published by several authors in the past and are pretty much defined as a central cavity or as a fine line or several lines which are typically comma shaped (Figure 1).

Figure 1: Several Keshi pearls sawn in half (top) and some radiographs with more or less evident features identifying the pearl as Keshi. The two pearls on the right represent the difficult pearls for which no reports are issued at the lab due to their lack of structure. They represent potential Keshi pearls. Photos and radiographs by Thomas Hainschwang. The problem that is occurring since some time is that more and more Pinctada pearls are submitted for identification that do quasi not exhibit any structure in radiography; it is being speculated (and has been confirmed by some dealers) that Keshi pearls from Pinctada sp. are being bought in quantities and pre X-rayed to potentially pass them off as natural pearls. This is one of the major challenges of the pearl laboratories these days. Currently another type of pearl has appeared in parcels of structureless Pinctada pearls, which showed perfectly naturally looking radiographs. Their identity remained mysterious, since they appeared to be evidently natural. Recently the GEMLAB Laboratory has received a parcel of golden, blue gray and white south sea pearls for analysis, which contained only pearls with very evident concentric structures and which appeared in some cases very rich in organic material (conchiolin) (Figure 2). The strong structure and the cracks made us think immediately about the radiographs of natural Pinna pearls, but since these were evidently Pinctadas and not Pinnas it appeared as if these were simply structure-rich natural nacreous pearls.

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Figure 2: Two pearls representative for the analyzed lot (left) and radiographs of the same parcel (right). The radiographs exhibit features which are thought - until today – characteristic for natural pearls. Photos and radiographs by Thomas Hainschwang. The conclusions drawn from these pearls - after discussion the radiographs with another pearl expert - were therefore that they were unusual natural pearls. Some weeks later one of the pearls came back for analysis since some details were not clear. The new testing of this particular pearl lead to a strong doubt on the identity of these structured pearls, particularly because of its unusual shape which resembled to a completely hollow Keshi pearl with on side irregularly flattened. The radiography of the pearl appeared to be ok, but a strong doubt remained, because the core portion of the radiograph looked a lot like the radiographs of Pinna pearls which are generally non-nacreous brown to black pearls. The Pinnas often show very strong concentric structures and commonly fractures within this structure because they tend to dry out (Figure 3).

Figure 3: A pearl of Pinna bicolor and the matching radiographs whhich exhibit rich structure and minor fissures. Photo and radiographs by Thomas Hainschwang. The isolated pearl that we received recently just after the preliminary analysis of the parcel was an 8 ct golden-coloured Pinctada maxima pearl which showed an equally extraordinary radiograph (Figure 4). The radiograph clearly appeared natural, but uncommon for a regular Pinctada golden pearl; also the shape of the pearl was somewhat strange, having the flattened bottom mentioned above.

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Figure 4: The golden pearl of Pinctada maxima and the matching radiographs which exhibit rich structure and many fissures, very reminessent of the features of Pinna pearls. Photo and radiographs by Thomas Hainschwang. After very detailed observation of various radiographs a suspicion arose that the pearl may be beaded – by a natural pearl. The central portion was so similar to Pinna radiographs that we asked permission to the client to saw the pearl in half to verify if this suspicion was correct or not and he very kindly allowed us to perform this uncommon method of identification. The pearl was carefully sawn in half, cooling it in order to avoid overheating, and the result of this very destructive test was as suspected, but nevertheless very disturbing: the pearl contained a brown pearl in the core, thus was cultured by the use of a natural brown pearl (Figure 5 and 6)!

Figure 5: The pinctada maxima pearl shown in figure 4 after having been sawn in half, and the very disturbing surprise associated with it – the dark brown structured portion of the pearl was identified as a natural Pinna pearl. Photo by Thomas Hainschwang.

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Figure 6: A close-up of the sectors where the natural pearl and the external golden layer of nacre of the cultured pearl meet. Photo by Thomas Hainschwang. The pearl used for culturing this Pinctada maxima pearl appeared to evidently a specimen belonging to the species Pinna, which typically shows a structure consisting of prismatic hexagonally shaped crystals of calcite (Figure 7), in contrast to the aragonite of which all nacreous pearls are composed. Figure 7: A close-up of the natural Pinna pearl “bead” shows the characteristic calcite prisms of which such pearls consist. Photo by Thomas Hainschwang. The sure identity of the bead-pearl was achieved by FTIR spectroscopy; the spectra of the nacreous part and the non-nacreous dark brown “bead” pearl were recorded and effectively aragonite was found for the nacreous part, while the “bead” pearl was identified as being calcitic (Figure 8). This result confirms the identity of this pearl belonging to the species Pinna, since only Pinna and Scallop pearls are calcitic.

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Figure 8: The specular reflectance FTIR spectra of the golden nacreous surface (red trace) matches the aragonite reference while the spectrum of the brown non-nacreous pearl used to culture this pearl (blue trace) matches the calcite refernce. Although only one pearl has been confirmed 100% to be a Pinna-beaded cultured pearl, several of the pearls in the parcel showed radiographs of the same type, which is not conclusive for their identification, but very suspicious. The sample radiograph shown below (Figure 9) has been recorded for a larger pearl of the same visual appearance that was part of the same parcel of pearls analyzed at the lab; the radiograph is of the same type, therefore it is likely that the pearl is also Pinna-beaded. The structure of this pearl is rather convincing and it appears that the Pinna that has very likely been used for this pearl was large and only short culturing time was involved, thus a rather thin layer of nacre can be seen. The point with pinna pearls is that they can be rather large; Pinna bicolor for example can form quite symmetrical pearls with diameters of >>15 mm. This means that large “Pinna-beaded” pearls must be expected to appear in the market.

Figure 5: A larger pearl from the same parcel exhibiting a similar type of radiograph but apparently only one layer of nacre. Although unconfirmed this pearl appears to be of the same Pinna-beaded type of cultured pearl. Radiograph by Thomas Hainschwang

Non nacreous brown „bead“ pearl – Calcite Nacreous „golden“ surface of the pearl – Aragonite

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The occurrence of cultured pearls beaded by the use of natural Pinna pearls is an extremely disturbing incidence which will make the determination of natural pearls once again more problematic. The most disturbing point of this type of culturing is that it represents one of the rare cases were a human intervention in a gemmological issue can only be defined as an attempt to commit fraud. There is absolutely no excuse to legitimate this type of culturing, since the natural pearl “bead” has no advantage whatsoever over the use of a regular bead, in contrary: it is more expensive, more irregularly shaped, more difficult to find and it will neither make better nor more beautiful pearls; the only thing it does is making the identification of such cultured pearls much more difficult. Therefore the only reason for this type of culturing is the attempt of unjustified enrichment by some unscrupulous individuals. On the potential volume of pearls produced by this new method only estimates can be made; pinna pearls are not very rare and they are hard to sell since they are generally not very attractive. It is not difficult though to find several kilos of these pearls if one knows the sources; therefore it is possible that these are not just some pearls floating in the market but that there may be a major attempt of fraud going on. Concerning the identification of such pearls: the ID can be very challenging and sometimes impossible; in many cases a pearl will likely be undeterminable as much as can be said for the moment. We are currently working on techniques to allow unambiguous identification of this material. The current situation in the market has led us to decide that for the time being, at least until mid-June, we at the GEMLAB laboratory will stop issuing reports for Pinctada pearls except for evident cases such as pearls in ancient jewelry pieces of known provenance.

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GEMNOTES

Short Papers

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Rare “Umbrella Effect” on a Pear-Shaped Irradiated Green Diamond By Emmanuel Fritscha) and Thomas Hainschwangb) a) Institut des Matériaux Jean Rouxel (I.M.N.), Nantes, France ([email protected]) b) Gemlab laboratory, Balzers, Liechtenstein. ([email protected])

A 2.79 ct pear shape green diamond was submitted to Gemlab, Balzers, Lichtenstein, for origin of color identification. Upon examination in the microscope, marked green color zoning following the faceted shape was noticed near the culet and “keel line” of the stone (fig 1).

Figure 1: Dark green color zoning following the faceted shape of this 2.79 ct pear shape diamond. Photomicrograph by Emmanuel Fritsch

Immersion in diiodomethane helped to observe that the color zoning followed some of the facet-edges surrounding the culet, but disappeared near the girdle. No color zoning was noticed near the girdle or under the table, looking from all possible directions. Increasing magnification demonstrates that the zoning was actually a sharp layer of green coloration following the facets, with a depth of penetration of approximately 0,1 mm (fig 2).

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Figure 2: Using immersion in diiodomethane reveals that the pattern seen above results from a sharp layer of green color approximately 0.1 mm deep under the facets surrounding the culet and keel area. Photomicrograph by Thomas Hainschwang The zoning observing in this gem is of the same nature as the “umbrella effect”, well known to result from irradiation using cyclotron radiation. This was performed from the 1940s until possibly the 1970s, but later replaced by more convenient irradiation techniques (see for ex. Gems & Gemology in review, Treated Diamonds, J.E. Shigley Ed., 2008, and references therein) . The presence of color zoning only on the culet side of the stone, and not near the table, indicates that this gem was “bottom treated”. The name “umbrella effect” results from the general appearance of this zoning for a round stone. The present sample offers the same effect for a pear shape, therefore it does not resemble an umbrella anymore, but we use that same expression for convenience. To our knowledge, photographic documentation of the effect for this shape is quite rare. The combination of this now rarely seen effect with this shape makes this stone almost a collectors item, despite the fact that it is unequivocally treated.

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Table of contents GEMLAB Laboratory News May 2010....................................................................... Page 3 Important Note Concerning Pearl Reports............................................ Page 3 New Instruments at the Lab............................................................... Page 3 The GEMMOSCIENCE Group.................................................................................. Page 4 GEMNOTES Important Laboratory Alert................................................................... Page 5 - 11 GEMNOTES Short papers...................................................................................... Page 12 Irradiated Diamond with Umbrella Effect.............................................. Page 13 - 14

GEMNOTES Vol.1, No2, May 2010

Technology

Gemnotes 16-05-10