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Dr. Hanco Zwaan


Figure 1: Rough diamond with a common crystal shape (octahedron), 25.19 carats, from Siberia, Russia.
Figure 2: Rough diamond with an uncommon shape, over 20 carats. These crystals not only are a challenge to diamond cutters, they also contain valuable



Figure 3: Green to bluish green diamonds are most often artificially colored by irradiation in a laboratory. Unambiguous criteria have yet to be found to distinguish natural green to bluish green diamonds with confidence.
  Gemstones come under the loupe at the 5th European Gemmological Symposium in the Netherlands

by Guest Blogger Dr. Hanco Zwaan
July 9, 2013


The European Gemological Symposium is a biennial symposium that is held in Europe, every time in a different country. This year it took place for the fifth time the Netherlands, on June 15 and 16. Organized by the Netherlands Gemmological Laboratory and the Dutch Gemmological Guild, and attracted more than 100 participants, not only from the Netherlands, but also from Belgium, Germany, France, Italy, England, Thailand and Canada.

On the first day of the symposium the participants visited Gassan Diamonds in Amsterdam, where they received an explanation of the history of diamond cutting in Amsterdam and to see the way in which business is done today, which is mainly selling, cutting only marginally still takes place. The company showed them polished diamonds, such as the Gassan 121 cut (a round brilliant with 121 instead of 57 facets), and especially for the symposium group a collection of rough diamonds. There were a number of large crystals to admire from Yakutia, Siberia, both ordinary and very unusual shapes (Figure 1 and 2).

The following day, at Naturalis, the Natural History Museum in Leiden where the Netherlands Gemmological Laboratory is housed, eight lectures were dlivered by a number of internationally renowned experts.

Professor Emmanuel Fritsch from the University of Nantes, France, precisely dealt with the huge variety of shapes that diamonds display, and explained that understanding these forms is of great importance when interpreting growth structures in polished stones. This is of particular significance when distinguishing between natural and laboratory-grown diamonds.

More about diamonds, especially color analysis, was covered by Thomas Hainschwang from GGTL Laboratories, Liechtenstein. Green to bluish-green diamonds owe their color to either local natural radiation present in the Earth, or to artificial irradiation in the laboratory (figure 3). In many cases there is not enough scientific evidence that a green diamond actually has a natural color. It is obviously very attractive financially, to receive a report, stating that the color of a green diamond is natural, indeed, a statement on a grading report that "color cannot be determined with certainty," could result in the diamond being 200 times less valuable. By patiently studying, and collecting data of untreated historical green diamonds in museum collections, it is hoped that an unambiguous method and clear criteria can be found to make distinction of natural green diamonds possible in the future.

Stefanos Karampelas, a researcher at the Gübelin Gem Lab, Switzerland, gave an overview of the methods used in pearl testing. It is clear that the game is not just about the distinction between imitation, cultured and natural pearls anymore, but it is also necessary to answer questions like "where did the pearls come from: from fresh or salt water," and "from which oyster, "Pinctada fucata, Pinctada Maxima or Pinctada Margaritifera?" Determining the authenticity of the color is of great importance as well, and there is also demand for the evaluation of the quality of the pearls, involving shape, color, luster, surface quality, and the quality and thickness of the nacre.

Ulrich Henn from the German Gemmological Association, paid attention to the multitude of color treatments that occur in quartz. He focused especially on translucent and opaque, fine-grained varieties. Knowing and understanding all the treatments becomes a necessity, for example, when one has to distinguish valuable chrysoprase from artificially irradiated, green colored chalcedony.

Ken Scarratt, from GIA Thailand, gave a clear presentation on the importance of systematically creating reference collections and gathering data, especially when it comes to determining the origin of a gemstone. He gave many examples of overlapping properties of gemstones (inclusions, chemistry) from very different areas, especially from relatively new sites. Mistakes will easily be made when a non-methodological approach is taken, based on observations and experience only.

Tobias Häger from the University of Mainz, Germany, gave an overview of the properties of natural spinel from Vietnam, and synthetic spinel, and made a comparison with various analytical methods.

Benjamin Rondeau from the University of Nantes, France, gave a fascinating overview of the characteristics and geological genesis of opal, both from Ethiopia, and from Australia. Ethiopia is a great new source of very fine precious opal. However, it must be taken into account that some unstable opals may potentially still enter the market.

The symposium ended with a contribution of Maggie Campbell Pedersen from the United Kingdom, about amber, a fossil resin, and all possible treatments that are applied; about the difference between amber, copal, recent resin and downright fakes. In the market many products are called "amber" without adding any information or disclosure of treatments, which is very misleading and confusing to the consumer. In order not to lose consumer confidence, this situation will soon have to change drastically.

All in all, the symposium was very informative, and both the participants as well as the presenters were excited about the high level of information. , I take part in discussions on nomenclature issues and ways to improve consumer confidence in various forums, including CIBJO, the World Jewellery Confederation; the Gem Industry and Laboratory Conference (GILC), and CEN and ISO. In my opinion, the presentations held at the European Gemmological Symposium again underline that these issues cannot be ignored or neglected, and that up-to-date, factual information and insight into the current status of the market is vital to get the most needed and accurate information to the final consumers.

For more detailed summaries of the various contributions at the symposium see www.naturalis.nl/nel, under 5th European Gemmological Symposium, programme and abstracts (http://www.repository.naturalis.nl/record/448764).

About the author
Hanco Zwaan is a researcher and curator at Naturalis, the National Museum of Natural History, Leiden, the Netherlands, and also head of the Netherlands Gemmological Laboratory. Dr. Zwaan has a PhD from Free University of Amsterdam on Geology, specializing on the formation of emeralds.
Apart from being an expert on emeralds, he also published articles on a variety of other gemmological and mineralogical topics. He co-authored the Edward Gbelin "Copper-bearing (Paraba-type) Tourmaline from Mozambique" which took first place in the Most Valuable Article of the Year Award in 2008. He took third place in 2012, with the article "Emeralds from the Fazenda Bonfim Region, RGN, Brazil," which was published in Gems & Gemology.

Hanco Zwaan is currently President of the Gemological Commission of CIBJO, the World Jewellery Confederation, dealing with nomenclature issues and laboratory best practices; and Executive Committee member of the International Gemmological Conference (IGC), and member of the Dutch NEN norm commission, dealing with the European ISO/CEN standard on consumer confidence and nomenclature in the diamond industry.

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