When pearl grading, the appearance of the surface of a pearl is one of the most important characteristics in determining its overall desirability and value. Ideally, the pearl's surface should be smooth, clean and shiny. It should have few, if any, bumps, abrasions, cracks or other surface flaws.
The pearl's surface lustre is critical. Lustre measures the brilliance and reflectivity of a pearl. The more brilliant and mirror-like the surface of the pearl is, the higher its quality. A dull or chalky surface indicates an inferior pearl.
Almost no pearl will have a perfect surface, however. Some flaws or irregularities are almost certain to be found on any pearl. The way to judge the degree to which these imperfections may affect the value or quality of the pearl is to examine how visible or obvious they are and also whether or not they will affect the durability of the pearl.
Chips, gaps or cracks in the pearl's surface are the most serious flaws, because they can cause the pearl to break or peel, thus destroying both its beauty and its value. Flaws such as these can greatly impact the value of even the most otherwise high-quality pearls. This is very important to watch for when grading pearls.
Less-serious problems are minor scratches or abrasions, which may affect small areas of the pearl's lustre or colour; small spots or variations in the pearl's colouring and tiny bubbles or wrinkles in the pearl's surface. Irregularities such as these generally do not indicate a weakness in the pearl's structure (such as a crack would) and they are often so small as to be virtually unnoticeable.