Nacre  Na"cre, n. of Oriental origin. A pearly substance which lines the interior of many shells, and is most perfect in the mother-of-pearl. [Written also nacker and naker.]           Source:      Webster\'s Revised Unabridged Dictionary (1913) 

Nacre is an organic mixture of calcium carbonate (CaCO3) in the form of platey crystals of aragonite and conchiolin (a scleroprotein).
Nacre is secreted by the ectodermic cells of the mantle tissue of certain species of mollusk. In these mollusks, nacre is continually deposited onto the inner surface of the animal\'s shell (the iridescent nacreous layer, commonly known as mother of pearl), both as a means to smooth the shell itself and as a defense against parasitic organisms and damaging detritus.
       When a mollusk is invaded by a parasite or is irritated by a foreign object that the animal cannot eject, a process known as encystation entombs the offending entity in successive, concentric layers of nacre. This process eventually forms what we call pearls and continues for as long as the mollusk lives. By Webster Dictionary  

      Nacre is what makes a pearl lustrous. When judging a pearl’s value thicker nacre is always better. Most of the time thicker nacre makes for a pearl with a greater luster.

. The first sign of thin nacre is a chalky appearance, or a flat non-lustrous look, dull. So a pearl with good thick nacre will be more lustrous.

       Thicker nacre generally creates a more lustrous pearl. Pearls with thicker nacre can last for decades. Thin nacre pearls will not last as long, therefore lowering the value.

       All pearls with thick nacre will not necessarily have a lustrous appearance. The quality of luster is dependent upon the translucence and the actual arrangement of the layers of nacre.

       When the nacre is very thick as in our higher grades of pearls, such as AA+ or AAA, the light is reflected off of the layers of nacre. It is this reflected light that gives the pearl it’s glow. The light reflected off the nacre, gives overtones and orient. These are accent colors that are in addition to the basic color of the pearl. Color, orient, overtones and quality, size and shape, all two things are taken into consideration when making a strand of matching pearls. 

       We recommend our clients buy pearl jewelry that is smaller but better quality. Especially if you are looking for an investment or an heirloom piece that will be passed down. The higher grades of pearls will increase in value. The lower grades with thin nacre will decrease in value with age ; because, the thin nacre will show wear. So, purchase pearls that are of a higher quality and smaller in size, AA+ or AAA.