The nacre quality is an important factor in the general appearance of the pearls. A thick coating is important for its durability. Whilst a thick coating does not guarantee a high lustre, generally thick coated pearls are more lustrous. In a thinly coated pearl the nucleus may be slightly visible (a flickering from dark to light when rotated) and in the case of a poor nacre, the pearl has a white dull, chalky appearance.
Just as few diamonds are flawless, few pearls are perfectly smooth. The presence of blemishes, whether slight, mild or severe, is called “spotting”. These are natural characteristics and do not forcibly diminish the overall beauty of the pearl. As good quality pearls spend at least two years in an oyster (one year for Akoya), it is rare to find a pearl completely devoid of any surface imperfections. Good lustre may highlight pearl blemishes. The quality of nacre, and in turn the lustre, is affected by a variety of factors such as: cultivation techniques, cultivation location, health of the mother oyster, the time of the year when the pearl is harvested, pollution, abnormally wide temperature variations, and the type of oyster used.
Types of blemishes
• Bump and welt: Raised areas, which are found alone or in groups
• Spot: An area that is darker or lighter than the surrounding nacre
• Discolouration: Spotty areas often caused from concentrations of conchiolin, the protein that holds the nacre crystals together • Chip: An fissure or a depression on a pearl's surface
• Pit and pinpoint: Tiny holes, depressions on the surface which are barely noticeable, found alone or in groups
• Gap: An area where the nacre has not covered the nucleus
• Dull: Area of very low lustre due to variations in nacre quality (chalky appearance) or contact with chemicals, cosmetics, or skin secretions
• Crack: Breaks in the nacre and/or bead nucleus. A small crack in the bead may look like a little hair trapped under the nacre. Cracks, even when not visible, can threaten the durability of a pearl. Thick nacre does not crack easily. Thin nacre does.
• Scratch: A straight or crooked line of a thin depression on a pearl's surface.
• Abrasion: Scratches on the pearl's surface resulting from damage
• Wrinkle: An irregular ridge or fold on the pearl's surface
For evaluation purposes, the following classification can be applied
• Clean: without blemishes or very small "spotting" that is not visible to the trained eye
• Slightly spotted: a few small surface irregularities visible to the trained eye, but generally clean look
• Moderately spotted: surface irregularities but one side of the pearl still clean
• Spotted: noticeable surface irregularities all over the pearl
• Heavily spotted: strong surface irregularities that affect the look of the pearl and threatens its durability
Blemishes are judged without magnification.
Buying on a budget, a consumer should be steered toward pearls with slight or mild spotting but having enough lustre to mask it.