To assess the value of a pearl, you must first understand the difference between a "natural" and a "real" pearl. Natural pearls are organically created within oysters. Humans have no part in their development. They are extremely rare. Most real pearls we see today are cultured pearls. They come from pearl farms. Nowadays, cultured pearls are so widespread that the term "pearl" generally refers to cultured pearls. Though pearls, natural or cultured, are rare jewels created within a living creature, their value is determined in much the same way as other precious gems. The appraisal factors take into consideration size, colour, surface, shape and lustre.
Measure the pearl's size. Pearls range greatly in size. The measurements are generally rounded to the nearest half or whole millimetre. The larger the pearl, the greater its value. Most familiar-size pearls are 10 to 15mm. Some pearl farmers have begun to cultivate even smaller pearls in response to market appetite.
Identify the pearl's colour. Colours can range from snow-white, black, silver, cream, yellow and sparkling gold. Overtone colours consist of pink, blue and green. Groupings of the most stunning and rarest colours such as silver-pink, white-pink and deep gold are much sought after.
Examine the pearl's surface. The pearl with less significant flaws is always more valuable. Examine the pearl's clarity, searching for blemishes, imperfections, spots and other irregularities. A good rule of thumb is that the more spotless the surface, the more valuable the pearl. Flawless pearls are very rare and go at a high price. Remember that pearls are an organic creation and do tend to have some natural defects.
Categorise the pearl's shape. Pearl shapes can include round (the rounder the better), teardrop, semiround, circle, oval and baroque. Perfect round and teardrop shapes are extremely rare and are the most valuable.
Scrutinise and establish the pearl's lustre. This is the most significant factor in formulating an opinion of a pearl's value. A pearl's lustre bestows the pearl with an unmistakable iridescence and depth. Lustre is determined by the depth of the pearl's nacre, often called "mother-of-pearl." It is formed when a combination of calcium carbonate and organic substances are secreted by the host species. Exceptionally lustrous pearls have a deep, mirror-like surface and a bright, shiny glow. Low-lustre pearls are dull.
Place a cultured pearl and an imitation pearl side by side. It is easy to notice the difference. Cultured pearls have an internal radiance, but imitation pearls only have an exterior shine. Imitation pearls, also known as "faux," or "semicultured," are not produced in anything living. Most are made of glass, plastic or shell beads. If you do this comparison on cultured pearls and fake pearls, the difference is incredibly perceptible.
Use the old-fashioned, reliable "tooth test." If you run the pearl along the edge of your upper teeth, the authentic cultured pearl will have a coarse feel, but the imitation pearl will be smooth.
When shopping for pearls, ask about the terms used in marketing the gems. For example, Majoica is an imitation pearl.