Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:


Fraud with cultured pearls can be detected

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:

More articles from Ecology, The Environment and Conservation:

nachricht Invasive Insects Cost the World Billions Per Year
04.10.2016 | University of Adelaide

nachricht Malaysia's unique freshwater mussels in danger
27.09.2016 | The University of Nottingham Malaysia Campus

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: New 3-D wiring technique brings scalable quantum computers closer to reality

Researchers from the Institute for Quantum Computing (IQC) at the University of Waterloo led the development of a new extensible wiring technique capable of controlling superconducting quantum bits, representing a significant step towards to the realization of a scalable quantum computer.

"The quantum socket is a wiring method that uses three-dimensional wires based on spring-loaded pins to address individual qubits," said Jeremy Béjanin, a PhD...

Im Focus: Scientists develop a semiconductor nanocomposite material that moves in response to light

In a paper in Scientific Reports, a research team at Worcester Polytechnic Institute describes a novel light-activated phenomenon that could become the basis for applications as diverse as microscopic robotic grippers and more efficient solar cells.

A research team at Worcester Polytechnic Institute (WPI) has developed a revolutionary, light-activated semiconductor nanocomposite material that can be used...

Im Focus: Diamonds aren't forever: Sandia, Harvard team create first quantum computer bridge

By forcefully embedding two silicon atoms in a diamond matrix, Sandia researchers have demonstrated for the first time on a single chip all the components needed to create a quantum bridge to link quantum computers together.

"People have already built small quantum computers," says Sandia researcher Ryan Camacho. "Maybe the first useful one won't be a single giant quantum computer...

Im Focus: New Products - Highlights of COMPAMED 2016

COMPAMED has become the leading international marketplace for suppliers of medical manufacturing. The trade fair, which takes place every November and is co-located to MEDICA in Dusseldorf, has been steadily growing over the past years and shows that medical technology remains a rapidly growing market.

In 2016, the joint pavilion by the IVAM Microtechnology Network, the Product Market “High-tech for Medical Devices”, will be located in Hall 8a again and will...

Im Focus: Ultra-thin ferroelectric material for next-generation electronics

'Ferroelectric' materials can switch between different states of electrical polarization in response to an external electric field. This flexibility means they show promise for many applications, for example in electronic devices and computer memory. Current ferroelectric materials are highly valued for their thermal and chemical stability and rapid electro-mechanical responses, but creating a material that is scalable down to the tiny sizes needed for technologies like silicon-based semiconductors (Si-based CMOS) has proven challenging.

Now, Hiroshi Funakubo and co-workers at the Tokyo Institute of Technology, in collaboration with researchers across Japan, have conducted experiments to...

All Focus news of the innovation-report >>>



Event News

#IC2S2: When Social Science meets Computer Science - GESIS will host the IC2S2 conference 2017

14.10.2016 | Event News

Agricultural Trade Developments and Potentials in Central Asia and the South Caucasus

14.10.2016 | Event News

World Health Summit – Day Three: A Call to Action

12.10.2016 | Event News

Latest News

Resolving the mystery of preeclampsia

21.10.2016 | Health and Medicine

Stanford researchers create new special-purpose computer that may someday save us billions

21.10.2016 | Information Technology

From ancient fossils to future cars

21.10.2016 | Materials Sciences

More VideoLinks >>>