In the spring of 2017, the Gübelin Gem Lab received a yellow pearl necklace for testing. The size and color of the specimens implied that they were South Sea cultured pearls. The high insurance value appeared to confirm this; however, there were some suspicious color patches that suggested the material had been dyed.
Only a few months earlier, author LK visited the Hong Kong office of Grace Pearls, a large producer with a pearl farm and factory in China, to see their latest batch of freshwater cultured pearls. Grace Pearls developed a proprietary method to grow large freshwater pearls with bead, marketed as “Edison” pearls. These occur in all the known colors of traditional freshwater pearls, typically white, orange, pink, and purple. To complement their color range, they also offer yellow and black treated pearls ranging from approximately 12 to 18 mm.
The goods we saw at Grace Pearls had a wide range of qualities and prices. The lowest price for a strand of Edison pearls was approximately US$100, while the highest-quality yellow dyed pearls go for as much as US$2,000. Prices for top-quality white and pink natural-color pearls may reach up to US$40,000 per strand.
The Gübelin Gem Lab acquired from Grace Pearls a necklace of yellow dyed freshwater bead-cultured pearls to complement our extensive reference collection. The largest of these pearls measured nearly 17 mm. For study purposes, we deliberately chose a low-quality necklace showing color concentrations, slightly irregular colors from pearl to pearl, and slight blemishes on the surface (figure 1).
The grafting process, which Grace Pearls considers a proprietary method, appears to be similar to that of “Kasumigaura pearls” from Japan and “Ming pearls” from China, where the bead is drilled first and a tissue is partly inserted into the drill hole in order to introduce both tissue and bead at the same time during the implantation procedure (H.A. Hänni, “Ming pearls: A new type of cultured pearl from China,” Journal of the Gemmological Association of Hong Kong, Vol. 32, 2011, pp. 23–24). X-ray images clearly show drill holes in the beads of several of these cultured pearls, mostly in the smaller beads (figure 2), while larger beads, like the one in the center of figure 1, have only one drill hole. This may be due to a possible re-implantation into the pearl sac once the first pearl has been harvested. X-ray fluorescence (XRF) analysis gave Mn and Sr values consistent with those of freshwater pearls.
Upon testing, the necklace submitted by the client showed identical properties: dark yellow color concentrations around drill holes and in cavities, uneven surfaces with various shades of yellow (figure 3, left; see also C. Zhou et al., “Update on the identification of dye treatment in yellow or ‘golden’ cultured pearls,” Winter 2012 G&G, pp. 284–291), X-rays showing an additional drill hole through the bead in some of the pearls (figure 3, right), and the chemical composition of freshwater pearls (figure 4). This demonstrates the importance of staying informed on new developments in the market.