MARINE RESOURCES AND AQUACULTURE

Source: http://ec.europa.eu/

Over 75 years ago, Japanese innovator Kokichi Mikimoto shovelled 720 000 pearls into a burning furnace. His actions reverberated around the world and across time itself. By showing his willingness to destroy so many pearls, he made a commitment to sell only the very best and to destroy the rest. To this day, Japanese pearls demand and receive a premium. As a result, many try to pass off their pearls as Japanese, even though they may come from elsewhere. Now two scientists from Germany have developed a method to determine the birthplace of pearls.

Pearls have long held the imagination of people around the world. © Shutterstock

Pearls: their beautiful translucent nature has captivated the hearts and minds of people for centuries. Up until the beginning of the 20th century, pearls had to be hunted by expert divers. These divers would free dive up to 40 meters below the water's surface and gather pearl oysters from the ocean floor. It wasn’t until two Japanese entrepreneurs were able to apply the pearl culturing technique an Australian scientist that pearls were able to be farmed.

Since then, Japan has been the heart of pearl farming, producing some of the world's finest round cultured pearls. More recently however, China has managed to outstrip Japan in terms of pearl production, but not in terms of price. Japanese pearls still cost up to ten times more than their competitors' across the sea of Okhotsk. As a result, some sellers have been trying to masquerade Chinese sweet-water cultured pearls as Japanese.

This poses a big problem for both consumers and scientists, because even experts find it difficult to distinguish between the two with the naked eye. That’s why two scientists from the Johannes Gutenberg University of Mainz Germany have devoted the past two years to coming up with a solution to this problem. What they were able to develop was a trace-element analysis technique which is able to determine a pearl's place of origin.

The two scientists in question, Ursula Wehrmeister, a gemmologist, and Dorrit Jacob, a geochemist, initially suspected that the Chinese manufacturing process consisted of high-production volumes accompanied by high levels of stress for the animals used in the cultivation process. According to Ursula Wehrmeister, Chinese farmers implant up to 60 cores into one oyster — a form of biological mass production. The stress caused by such mass production would result in a number of unusable or misshapen pearls, which would not be able to be processed by jewellers.

The problem of vaterite would also become more common. 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.

The scientists were therefore able to use a process known as laser ablation ICP mass spectrometry, to determine whether pearls contain vaterite, as well as determine whether certain sapphires have been subsequently treated. Specifically, a UV laser is used to cut a microscopically small sample, roughly an eighth the diameter of a human hair. This micro-sample is then rinsed into the analysis device with the aid of an inert gas and the content of trace elements. Based on the outcome of this process, the birthplace of a pearl is able to be determined.

This technique according to Dorrit Jacob, is also applicable to gems other than pearls. 'The large number of especially orange- and blue-coloured 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 coloured more brightly with beryllium,' he said.

With such a wide potential for this technique's application, consumers can begin to rest assured that they are getting what they pay for.