A standardized terminology has not been developed for pearl blemishes.
The terms found below are based primarily on those listed in the GIA (Gemological Institute of America) pearl grading course. These imperfections are usually judged without magnification.
Some typical pearl blemishes- pits, bumps, welts, holes, pinpoints and dull area
Straight or crooked lines scraped on the pearl. These aren't serious unless the pearl is so badly scratched the luster and beauty is affected.
Breaks in the nacre and/ or bead nucleus. Small cracks in the bead may look like little hairs trapped under the nacre. Cracks, even when not visible, can threaten the durability of a pearl.
u Dull Spots
Areas of very low luster due to variations in nacre quality or contact with chemicals, cosmetics or skin secretions.
Circular depressions or indentations which are often found in groups.
u Pits and Pinpoints
Tiny holes on the surface which are normally hardly noticeable and, therefore, not serious. "Pinpoints" may also refer to tiny bumps since, from a distance, these look about the same as tiny pits.
u Chips, Holes and Patches of Missing Nacre
Blemishes which may occur on any type of pearl but that are particularly common on those with thin nacre.
Spotty areas often caused from concentrations of conchiolin, a protein substance that holds nacre crystals together. Discolorations are not frequently seen because pearls are typically bleached to even out their color.
Raised areas which are found alone or in groups. They may sometimes cover most of the surface area of the pearl. If bumps or welts are very large, they can put the pearl into the off-round category. Occasionally pearls have a wrinkled appearance. This is due to groupings of welts.