2020

Chasing Cultured Pearls at SSEF: Cultured Pearls using a Natural Pearl as a Bead

Figure 1: Too perfect to be true. A parcel of 19 cultured pearls with mixed structures, from ‘classic’ beaded to beadless, and even using a natural pearl as a bead, see following short note. Photo: V. Lanzafame, SSEF

As a leading pearl testing laboratory worldwide, the SSEF has analysed in the past few months a large number of pearls for our clients. Besides natural pearls of impressive size or historic provenance (e.g. the pearl pendant of Marie Antoinette and the so called Dodge pearls), we regularly identify and sort out cultured pearls which were mixed intentionally or non-intentionally into pearl parcels.

Apart from the usual suspects, i.e. beaded and beadless cultured pearls with characteristic structures, we occasionally also encountered cultured pearls with uncommon features and structures (Figure 1), such as cultured pearls using a natural pearl as a bead, worth mentioning in a short note to remind the trade about this cultured product.

Reported already years ago (Krzemnicki 2010, Hainschwang 2010), natural pearls of low quality can be used as a bead to produce a cultured pearl of larger size and better quality. So far, we have seen these cultured products mainly produced within Pinctada maxima and Pinctada margaritifera shells. In the past year, we have again seen a few such samples, ranging in size from 8 – 12 mm, mostly mixed in parcels of undrilled or drilled pearls.

Figure 2: Radiography showing a cultured pearl with a natural pearl as bead. The natural pearl is darker grey as it contains more organic matter interlayered within the tiny radially arranged calcite columns. The surrounding nacre overgrowth (bright grey) of this cultured pearl shows nearly no internal features apart from a cavity structure along the nacre/bead intersection. Radiography: J. Braun, SSEF
Figure 3: Cultured pearl with natural pearl as bead of 5.8 ct (9.5 mm diameter) and X-ray microtomography cross-section image showing the natural pearl bead (dark grey) surrounded by cultured nacre overgrowth (bright) and with an irregular empty cavity (black) adjacent to the bead. Tomography: J. Braun, SSEF

Although it is possible to already spot this through meticulous X-ray radiography analysis (Figure 2), these cultured pearls are best identified using X-ray microtomography (Figure 3), which provides a threedimensional analysis of the internal pearl structures at high resolution. The characteristic features are a clear demarcation line between the natural pearl bead and the cultured nacre overgrowth, often with a more or less conical to irregular cavity structure adjacent to the bead structure, very similar to those observed in many traditional beaded cultured pearls. Another striking feature in many of these cultured pearl products is the obvious different texture of these two parts, with the natural pearl bead mainly or completely formed by columnar calcite with many drying fissures and a nearly perfect and uniform nacre overgrowth with nearly no drying fissures.

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