What is Pearl Luster?
Luster is essentially the deep reflective iridescent quality or brilliant shine of the surface of the pearl. The Pearl shines and reflects light and images. The deeper this reflective quality the better and more valuable the pearl will be. Pearls with lower luster will appear white or chalky, rather than brilliant and shiny.
In general, saltwater pearls tend to have greater luster than freshwater pearls. However the higher qualities of AAA freshwater pearls are as lustrous as the saltwater pearls. Quality is what luster is all about.
The thickness of the nacre has a great deal to do with the luster of the pearl. The length of time given a pearl to form will mostly help determine the ultimate result of the luster. Freshwater pearls take between 3 and 6 years to develop while saltwater pearls take between 8 and 26 months to develop.
Freshwater pearls are almost 100% nacre due to the nucleation process used. When nucleating freshwater pearls, a small piece of “tissue” cut in a square is used instead of the standard bead used for saltwater pearls. As a result the freshwater pearl is almost completely made up of nacre. When a freshwater pearl is described as having 4mm of nacre then the pearl is 8mm in diameter as the measurement is calculated from the center of the pearl. Some farmers have started to use beads with freshwater pearl nucleation in hopes of producing a consistently round pearl. Their experiments have been successful so far. Because of these innovative techniques, freshwater pearls have now developed into prized possessions. Some having luster comparable to saltwater pearls, and still being perfectly round.
Saltwater pearls have substantially less nacre, however they still do possess a deep luster which can be attributed partially to the length of time allowed to develop the pearl and the composition of the nacre. Saltwater pearls are always nucleated with a piece of mantle tissue as well as a round bead. They are much more consistent in producing round pearls with brilliant luster. When a saltwater Akoya oyster is nucleated with a 4mm bead, then typically it will create a nacre thickness of 1mm to 2mm producing a resulting pearl size of 6mm to 8mm.
One must be careful when examining the luster of a suspect pearl. There are some treatments that all pearls go through after being harvested, such as cleaning and polishing. However, some pearls that are not up to par can have their luster heightened by untrustworthy pearl processors. Luster can be artificially enhanced by a coating that will only be temporary. Sold to an unknowledgeable consumer, the pearl coating will eventually chip or peel, leaving the dull, low-luster pearl underneath.
Luster treatments are not always easy to spot. The best way to date is to place the pearl under a microscope, with magnification of at least 50X. The pearl with a treatment will appear smooth on the surface, where an untreated pearl will have a scaly surface due to the composition of nacre.