Abstract Gems & Gemology, Spring 2013, Vol. 49, No. 1

Perles de Culture de la Mer de Cortez: Les Belles Inconnues [Unknown Beauties: Cultured Pearls from the Cortez Sea]

The first part of the article gives a historical survey of pearls from the Sea of Cortez (Gulf of California), followed by an account of the actual situation. Black pearls and nacre have been known since pre-Columbian times and were much coveted in Europe after the Spanish conquest. In the 16th century, the coastal city of La Paz became the main commercial center for nacre and pearls. The most famous pearl from this source is “La Peregrina,” a 203.8-grain gem last owned by Elizabeth Taylor, and John Steinbeck’s story “The Pearl” also takes place there.

While nacre production was predominant in the first half of the 19th century, black pearls were very much in fashion in the middle of the century. From 1893 to 1914, José Gourieux was the first to cultivate Pteria mazatlanica black-lipped oysters from La Paz for their nacre. He produced about five million oysters per year, of which 10% contained natural pearls. Although these were only a by-product, they led to a sharp decline in pearl diving. In 1914, the plant farm was destroyed during the Mexican revolution. The appearance of artificial substitutes for nacre, overfishing of the oyster banks, and a mysterious infection of the oyster larvae in 1939 finally led to the prohibition of all pearl diving a year later.

After attempts to renew pearl cultivation in the 1960s and 1970s, which failed largely because of political influences and the commercial success of black Tahitian pearls, three students of the Monterrey Institute of Technology and Superior Studies set up a small farm on the campus at Bacochicampo Bay in Guaymas. Their intent was not the industrial production of pearls but the development of environmentally sound and “oyster-friendly” methods of cultivation, which is why the oysters are implanted only once and harvests are small. The 2011 harvest consisted of 1,783 pearls, or 1.7 kg, as compared to 50 tons of Akoya pearls, 11 tons of South Sea pearls, 12 tons of Tahiti pearls, and 1,800 tons of Chinese freshwater pearls.

The other pearl-producing oyster of those waters, the rainbow-lipped Pteria sternia, yields black pearls with many different overtones. The young oysters are all harvested in the sea. Before the implantation of nuclei, the oysters are X-rayed. Some 3% contain natural pearls, and these oysters are not implanted. The pearls are sold as “natural,” though purists would dispute this description. The oysters with nuclei are cultivated for 18–24 months. The diameter of the cultured pearls ranges from 8–12 mm (3.2–4.8 inches), the thickness of the nacre from 0.8 mm–2 mm (0.3–0.8 inches). The pearls are black and very iridescent and show various strong overtones, including red (“cranberry”). Their luster is somewhat more silky than that of the Tahitian pearls. Unlike most other cultured pearls, they are not treated in any manner, except for rinsing with water. They show a pink to red UV fluorescence, which is characteristic of pearls from the Sea of Cortez.

The future is uncertain, however. The volume of larvae has dropped significantly because of global warming effects, damage to the oyster cages from fishing boats, and the fragility and sensitivity of Pteria sternia.

Abstracted by Rolf Tatje