Gem News International Gems & Gemology, Summer 2017, Vol. 53, No. 2

Dyed Yellow Beaded Freshwater Cultured Pearls Imitating South Sea Cultured Pearls

Uneven color and blemishes on low-quality cultured pearl necklace.
Figure 1. Uneven color and blemishes on the surface of a low-quality dyed cultured freshwater pearl necklace obtained from Grace Pearls. Photo by Lore Kiefert.

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.

X-ray images of dyed freshwater cultured pearls.
Figure 2. X-ray image of yellow dyed freshwater cultured pearls. The beads range from approximately 10 to15 mm in diameter, while nacre thickness varies from <0.2 to >5 mm. Some of the beads show an additional drill hole. Image by Pierre Hardy.

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.

Left: Blemishes and dark color concentrations. Right: Bead within pearls.
Figure 3. Left: Blemishes and dark color concentrations in cavities on the surface of dyed cultured freshwater pearls in a client-submitted necklace. Photo by Lore Kiefert. Right: An X-ray image of two pearls from the client necklace showing a clear bead. The left pearl displays an additional drill hole in the bead. Image by Pierre Hardy.
Plot of theoretical distribution of MnO vs. SrO in freshwater and saltwater pearls.
Figure 4. A plot showing the theoretical distribution of MnO vs. SrO in freshwater and saltwater pearls (after W. Gutmannsbauer and H.A. Hänni, “Structural and chemical investigations on shells and pearls of nacre forming salt- and fresh-water bivalve molluscs,” Journal of Gemmology, Vol. 24, No. 4, 1994, pp. 241–252). The red dots represent values for our reference collection necklace, the yellow dots the values for the client-submitted necklace.

Lore Kiefert is chief gemologist, and Pierre Hardy is senior gemologist, at the Gübelin Gem Laboratory in Lucerne, Switzerland.