Summer 2009

Cultured Pearls from Fiji

At the BaselWorld Watch and Jewellery Show in April 2008, Gerhard Hahn Pearl AG (Düsseldorf, Germany) displayed some variously colored cultured pearls (figure 1) from a relatively new source, the South Pacific island nation of Fiji. So far, Fijian production has been limited, coming from two pearl farms located ~60 km apart on the island of Vanua Levu, in Savusavu Bay and Buca Bay. The cultured pearls are harvested from Pinctada margaritifera oysters, which are grown from spat collected in waters of the Savusavu area. The oysters are implanted with round bead nuclei (minimum 7.5 mm in diameter) and harvested 12–18 months later. They average 10.8 mm in diameter at first harvest (i.e., before reinsertion of beads for a second harvest). They mostly range from light bluish green to the popular “chocolate” brown, and Gerhard Hahn Pearl AG indicated that their colors do not result from treatment; only standard post-harvest processing such as cleaning is performed.

Up to 65% of the production show lighter colors than those that are typical of P. margaritifera cultured pearls. Since some resemble bleached P. margaritifera products (see, e.g., Summer 2008 Lab Notes, pp. 159–160), Gerhard Hahn Pearl AG donated 20 samples to GIA for documentation purposes, and they were studied at the New York Laboratory by Akira Hyatt and Dr. Wuyi Wang.

Based on GIA’s examination over the years of many thousands of P. margaritifera cultured pearls, the broad range of bodycolors in this relatively small sample set was remarkable. The hues ranged from blue and green (cool hues) to orange and yellow (warm hues), with many samples showing strong saturation. P. margaritifera cultured pearls typically occur in the cooler hues, with darker tones showing higher saturation and lighter tones showing lower saturation. In contrast, those from the Pinctada maxima oyster typically show warm hues, with higher saturation in the lighter tones and lower saturation in the darker tones. The Fijian cultured pearls were split  between warm and cool hues, and many of the cool hues exhibited a lighter tone, often with relatively high saturation. Some also exhibited colors generally seen in P. maxima cultured pearls (i.e., yellows, but with darker tone and stronger saturation), while others resembled treated “chocolate” pearls (orangy/pinkish browns) from P. margaritifera. (Note that in lower saturations, warm hues appear brown or brownish, while cool hues appear gray or grayish.) The diverse color range of the cultured pearls is also seen in the host P. margaritifera shells (e.g., figure 2).

UV-Vis-NIR reflectance spectra are given in figure 3 for four categories of the Fijian cultured pearls: brown (five samples), yellow (seven), green (five), and blue (three). The brown samples showed decreases in reflectance due to absorptions at 290, 495, and 700 nm—believed to be related to organic pigments—that were superimposed on a nearly flat background. These spectral features are similar to those of naturally colored brown Tahitian cultured pearls. The absorptions at 290, 495, and 700 nm were also distinct for the yellow samples, but the overall spectra were sloped toward lower wavelengths. The absorptions at 495 and 700 nm were very weak in the green samples, but the 295 nm band was consistently strong. In addition, the slope of the spectra in the 400–700 nm region for the green samples was opposite that of the yellow samples. In the blue cultured pearls, the three bands related to organic pigments were clearly observed, and in general the reflectance increased with decreasing wavelength. The spectroscopic data indicate that all of the tested cultured pearls were of natural color. X-radiography showed that they were bead cultured, as represented by Gerhard Hahn Pearl AG.

The Fijian farms together produce ~40,000 cultured pearls (or 125 kg) yearly and have ~100,000 oysters under cultivation. The farms are operated by the J. Hunter Pearls Fiji Pearling Conservancy under the country’s Environmental Code of Practice, to ensure that any negative environmental impact is minimized.

Marisa Zachovay (marisa@hotpebbles.com)
Pebbles LLC, Delray Beach, Florida