Cultured and natural pearls identification

Cultured and natural pearls identification_1

The Swiss Gemmological Institute SSEF in Basel, Switzerland said it has been receiving large quantities of saltwater pearls for certification in recent weeks. These pearls are often accompanied with reports describing them as natural pearls, but their almost perfect appearance has raised doubts among many natural pearl dealers.
Having tested these pearls with advanced technology, including X-ray radiography, X-ray luminescence, X-ray micro-tomography and radio- carbon age dating, the SSEF found that many of these pearls are beadless cultured pearls.

Selection of beadless cultured pearls from pinctada maxima © SSEF, 2010

The arrival of large quantities of these “new” saltwater pearls, which are of far better quality than the many natural pearls treasured for centuries, represents a great danger to the natural pearl marke. This is especially true because  some individuals are purposely selecting those cultured pearls with the most intriguing and potentially confusing internal structures (using radiography) from the large stocks they purchase from pearl farms, so as to later introduce them onto the natural pearl market.  The cultured pearls in question are a by-product of beaded cultured pearl production and are sometimes described as keshi cultured pearls in the trade. Although these pearls do not show one distinct feature that explicitly characterises them as cultured, it is the combination of internal and external structures, which enable an identification of this material. The pearls are often either button-, oval- to drop-shaped, or baroque.
As the trade is overflowing with these beadless cultured pearls, the SSEF has taken measures to protect the natural pearl market from this threat. The first step is the use of more rigorous and specified definitions for natural and cultured pearls:
A natural pearl is a pearl which formed, without any human intervention, in a wild oyster or mussel living in its natural habitat, while any pearl stemming from a pearl cultivation farm is a cultured pearl.

Cultured versus natural pearls
The most common internal feature (radiography) of beadless cultured pearls is a small curved dark line or a larger curved cavity  at the centre of the pearl.

Small curved dark line in a beadless cultured pearl
Large curved dark cavity in a cultured beadless pearl (three dimensional view of micro x-ray tomography sections) © MS Kremnnicki

This feature is well known and reported. Another common feature of these beadless cultured pearls, so far not reported, consists of a round dark core made of fine circular chonchiolin layers, often with one or more small nacre points in the centre.

Dark centre with circular conchioline layers in a beadless cultured pearl

It  is this last feature which may be misinterpreted as an indicator for natural growth and leads to the wrong conclusion that the pearl is natural. As these pearls are often specifically, and often intentionally, drilled to hide internal structures, only careful radio-graphy and X-ray tomography analysis may reveal the true nature of these pearls.

The radiography of a necklace of white pearls  exhibits most of the characteristic internal structures (curved dark lines and cavities) that are typical of beadless cultured pearls. However, in some pearls these structures can only be traced using micro X-ray  tomography.
The uniformity in colour and surface condition of these white pearls are strong indication that they all originate from the same cultured pearls.

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