Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Fraud with cultured pearls can be detected

15.07.2008
Scientists at the Johannes Gutenberg University Mainz advise buyers of cultured pearls to be more vigilant. "In Germany too, we are increasingly seeing Chinese sweet-water cultured pearls being marketed as Japanese, although they actually originate from China," say Dr Dorrit Jacob and Ursula Wehrmeister of the Institute of Geosciences.

Even gemmologists, i.e. experts in precious stones and pearls, cannot distinguish between pearls from Japan and China with the naked eye. However, Japanese pearls can fetch a price ten times that of Chinese pearls. Over the past two years, the two scientists from Mainz University have developed a method that makes it possible to clearly identify the origin of pearls.

At the beginning of the 20th century, the Japanese managed to produce the first round cultured pearls. Pearl culture entails inserting small round pellets, usually made of oyster shell nacre, into the oysters. The important factor during this operation is that a small section of the mother-of-pearl forming tissue must also be implanted. The oyster then gradually coats the foreign body - the core - that has been introduced with many layers of nacre. In this way, a new pearl is produced over a period of two to three years. Cultured pearls can be produced in all regions of the world where natural pearls form. Most pearls on the market today are cultured pearls, as real pearls are rare - and expensive.

In China, sweet-water pearl farming now produces pearls for the mass market rapidly and with relative ease. "The oysters are easy to care for and the pearls grow very quickly and can be cultivated from a core or even from very small tissue samples," explains Ursula Wehrmeister. The gemmologist notes that Chinese farmers implant up to 60 cores into one oyster - a form of biological mass production. At the same time, Chinese pearl culture does produce some oddities: Large discs or hemispheres are implanted to obtain custom-made pearls for rings and ear-rings - even Mickey Mouse has served as a model. "Traditional Japanese sweet-water pearl farmers, on the other hand, implant only one or two cores, but are rewarded for their troubles with a very good quality", states Wehrmeister.

High production volumes, and possibly also the manner in which the oysters are cultivated, means that most of the Chinese yield consists of rejects that cannot be used. "We suspect that the animals are subjected to enormous stress," claims Wehrmeister, thus explaining one possible cause of this poor quality. The pearls they produce are not round, but misshapen and cannot be processed by the jewellery industry. The problem of vaterite is also becoming more common.

Mother-of-pearl, and thus also pearls, are biominerals consisting of calcium carbonate with a small proportion of organic substances, rather like a brick wall made from bricks and mortar. In particularly attractive, lustrous pearls, the inorganic calcium carbonate fraction is mainly made up of aragonite. The scientists from Mainz found that Chinese pearls contain more vaterite, not only within the pearls, but also on the outside, where the substance forms a matt surface with white spots, rendering the pearls unsuitable for sale.

High-quality Chinese pearls, however, cannot be distinguished from Japanese pearls with the naked eye, even by experts. "We can use trace element analysis to establish the origin of the pearls beyond doubt," explains Dorrit Jacob, a geochemist. A UV laser is used to cut an almost invisibly small sample in a size ranging of 5 - 100 micrometres from the study material (by way of comparison, a human hair has a diameter of about 40 micrometres). This mini-sample is rinsed into the analysis device with the aid of an inert gas and the content of trace elements, particularly barium and strontium, can then be established.

The ratio between barium and strontium in comparison with total strontium content indicates the origin of the material. "We have been developing this practically non-destructive test method since 2006 in order to distinguish between Japanese and Chinese pearls," says Jacob. "We are also able to use this method, known as laser ablation ICP mass spectrometry, to determine whether pearls contain vaterite and whether certain sapphires have been subsequently treated." The large number of especially orange- and blue-colored sapphires currently on the market cannot all be natural. This means that sapphires with a less marked coloration, which would normally not be marketable, have been colored more brightly with beryllium.

The next step for the two scientists will be to analyze coral in more detail and to create a basis for learning more about the structure and origin of this resource created by undersea creatures and the jewellery that can be made from it.

PD Dr. habil. Dorrit E. Jacob | alfa
Further information:
http://www.uni-mainz.de
http://www.biomin.uni-mainz.de/englisch/e_index.html

More articles from Ecology, The Environment and Conservation:

nachricht Safeguarding sustainability through forest certification mapping
27.06.2017 | International Institute for Applied Systems Analysis (IIASA)

nachricht Dune ecosystem modelling
26.06.2017 | Albert-Ludwigs-Universität Freiburg im Breisgau

All articles from Ecology, The Environment and Conservation >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Can we see monkeys from space? Emerging technologies to map biodiversity

An international team of scientists has proposed a new multi-disciplinary approach in which an array of new technologies will allow us to map biodiversity and the risks that wildlife is facing at the scale of whole landscapes. The findings are published in Nature Ecology and Evolution. This international research is led by the Kunming Institute of Zoology from China, University of East Anglia, University of Leicester and the Leibniz Institute for Zoo and Wildlife Research.

Using a combination of satellite and ground data, the team proposes that it is now possible to map biodiversity with an accuracy that has not been previously...

Im Focus: Climate satellite: Tracking methane with robust laser technology

Heatwaves in the Arctic, longer periods of vegetation in Europe, severe floods in West Africa – starting in 2021, scientists want to explore the emissions of the greenhouse gas methane with the German-French satellite MERLIN. This is made possible by a new robust laser system of the Fraunhofer Institute for Laser Technology ILT in Aachen, which achieves unprecedented measurement accuracy.

Methane is primarily the result of the decomposition of organic matter. The gas has a 25 times greater warming potential than carbon dioxide, but is not as...

Im Focus: How protons move through a fuel cell

Hydrogen is regarded as the energy source of the future: It is produced with solar power and can be used to generate heat and electricity in fuel cells. Empa researchers have now succeeded in decoding the movement of hydrogen ions in crystals – a key step towards more efficient energy conversion in the hydrogen industry of tomorrow.

As charge carriers, electrons and ions play the leading role in electrochemical energy storage devices and converters such as batteries and fuel cells. Proton...

Im Focus: A unique data centre for cosmological simulations

Scientists from the Excellence Cluster Universe at the Ludwig-Maximilians-Universität Munich have establised "Cosmowebportal", a unique data centre for cosmological simulations located at the Leibniz Supercomputing Centre (LRZ) of the Bavarian Academy of Sciences. The complete results of a series of large hydrodynamical cosmological simulations are available, with data volumes typically exceeding several hundred terabytes. Scientists worldwide can interactively explore these complex simulations via a web interface and directly access the results.

With current telescopes, scientists can observe our Universe’s galaxies and galaxy clusters and their distribution along an invisible cosmic web. From the...

Im Focus: Scientists develop molecular thermometer for contactless measurement using infrared light

Temperature measurements possible even on the smallest scale / Molecular ruby for use in material sciences, biology, and medicine

Chemists at Johannes Gutenberg University Mainz (JGU) in cooperation with researchers of the German Federal Institute for Materials Research and Testing (BAM)...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Plants are networkers

19.06.2017 | Event News

Digital Survival Training for Executives

13.06.2017 | Event News

Global Learning Council Summit 2017

13.06.2017 | Event News

 
Latest News

Supersensitive through quantum entanglement

28.06.2017 | Physics and Astronomy

X-ray photoelectron spectroscopy under real ambient pressure conditions

28.06.2017 | Physics and Astronomy

Mice provide insight into genetics of autism spectrum disorders

28.06.2017 | Health and Medicine

VideoLinks
B2B-VideoLinks
More VideoLinks >>>