Dr. Jean-Paul Lintilhac, installer and developer of two black pearl farms in Tahiti, is one example. In his book, Black Pearls of Tahiti, he states that jewelers in Tahiti are worried about the thinness of the nacre of some of the pearls offered to them for sale. He goes on to say that certain pearl farmers are in such a hurry to recover their investment that they harvest their pearls prematurely and as a result the nacre is very thin. Then he writes:

"Formerly a big pearl meant a good thickness of nacre, but with the supergrafts used today, size is no guarantee. If you are buying a big expensive pearl, you have the right to ask for an x-ray of it which will enable you to see and measure the thickness of the layers of nacre surrounding the nucleus. One millimeter of nacre is a minimum for a good pearl. "

Tahiti Pearls, a major black pearl company, also tells consumers in their book The Magic of the Black Pearl, that nacre thickness is a criteria used to judge black pearls. They indicate a 1 mm to 1.5 mm nacre thickness as an appropriate range for black pearls.

Hisada and Komatsu of the Mikimoto Co. put nacre thickness at the top of their list of pearl quality factors. They state:
"Nacre thickness is a basic factor in judging the elegance of the pearl. Its beauty and durability depend on the thickness of the nacre, its quality and quantity." The Mikimoto company, in their leaflet "The Art of Selecting Cultured Pearls," tells consumers: "For beautiful pearls the most important factors are luster and nacre thickness. Chapter Four gives guidelines on determining if the nacre thickness of Akoya pearls is acceptable. Unfortunately these techniques do not work as well on black pearls. It's often impossible to see into their drill holes because the pearls may be glued to a jewelry piece such as a ring or pendant mounting. Also the nacre of black pearls may mask the layers of a shell bead nucleus that might be visible in a thin-nacre Akoya pearl. Dealers use luster as a guide to nacre thickness because a good deep luster signals good nacre thickness.

Usually the best way of determining the nacre thickness of a black pearl is with an x-ray. And, if you are spending thousands of dollars on a pearl piece, it's well worth your money to have a gem lab x-ray the piece to check for nacre thickness and to determine if the color is natural. But what should you do if you are paying, say $500 for a black pearl pendant? An x-ray in a case like this is probably not worth the money. The best thing you can do is to choose pearls with as high of a luster as possible and buy your pearls from jewelers who consider nacre thickness important.