More about Nacre – Nacre is the thin top layer of the pearl surface.  It is responsible for pearl color and lustre, it’s also one of the prime value determinators.   In general the thicker the nacre the better.  Nacre is deposited in layers over time so a thin nacre pearl is much faster and cheaper to grow however thin nacre will also make the pearl’s color look uneven and prone to peeling and cracking.   Nacre also effects lustre, one of the key factors in a high quality pearl.  Thicker nacre tends to offer better luster and depth to the pearl’s color.  One way to check nacre thickness is to take a jewelers loop and look at the holes drilled into the pearl string (for bracelets and necklaces).   Look for several layers of nacre and a minimum of discoloration around the edge of the hole.  Many experts suggest a thickness of at least .4mm.  When in doubt get a second opinion from a qualified jeweler or gemologist.