Nacre, also known as mother-of-pearl, is a crystalline substance that creates the iridescent visual effect attributed to pearls. Nacre is an organic substance secreted by molluscs over an intruding irritant or implanted nucleus. It is a strong and resilient material that is lightweight and transparent, allowing light to pass through its surface, creating a subtle glow on the pearl’s surface.
Since nacre determines lustre, nacre quality is a critical factor when determining a pearl’s value. Generally speaking, the thicker the nacre, the more valuable the pearl. Thick nacre not only looks better than thin; it also is much more durable.
Freshwater pearls are almost completely nacre. They and their saltwater counterparts with thick nacre will look beautiful and last for many years.
Freshwater Pearls are of Solid Nacre
Freshwater Pearls differ from other cultured pearls, in that the great majority of them are not bead-nucleated. Freshwater molluscs are nucleated by introducing a tiny piece of mantle from a shell, which causes the formation of a pearl sac, where the tissue deposits calcium carbonate.
The resulting pearls are of solid nacre, but without a bead nucleus to guide the growth process the pearls are rarely perfectly round.