Nacre is the substance from which pearls are made. Since nacre determines luster, 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.
Nacre Quality Classifications
Nacre quality is usually broken up in three categories:
Note: If dealing with quality pearls, they should fall into the "acceptable" category
Nacre Value
Pearls that are chalky, dull or that blink aren't as attractive as those that are gleaming and solid, they also won't be as durable. Freshwater pearls are almost completely nacre. They and their saltwater counterparts with thick nacre will look beautiful and last for many years.
Pearls with thick nacre have more of a chance of having a high-quality luster. The arrangement and translucence of each nacre plate determines the luster. Some thick-nacre pearls lose points when it comes to value because they don't have great luster.