Each of the factors that may contribute to perfection are rarely found together in one pearl.
Value is determined by the best combination of size, lustre, colour, surface quality and shape.
Size and weight
This will depend on the age or type of oyster in which the pearl was found. A large pearl will not necessarily be valuable if any of the other features is poor. Arabic names for size also hint at overall quality, with Dana being the most perfect, large and therefore valuable. Following this in descending order are Hasabi, Ras, Betten, Thail, Rubia¡'a and Satheet. Until fairly recently pearls were weighed in grains, with four grains equalling one carat. Today pearls are sold by carat weight and their size is measured in millimetres.
The most sought after shape is symmetrical. Baroque pearls are irregular in shape but can be very valuable if the lustre and size is excellent.Teardrop and pear-shaped pearls are also highly prized.
Top quality pearls are colourful, like an oyster shell.The highest prices are often paid for pearls that are silvery white or have a light pink tint.In the Gulf, pearls with a golden hue are the most highly prized.
The difference between a pearl with very high lustre (sharp, mirrorlike reflection) and very low lustre (milky or chalky appearance) is easy to detect. The majority of pearls fall into the low and medium lustre range.
The presence of flaws, in the surface of the pearl, are not necessarily important. However if the flaws are very prominent the value of the pearl will be reduced.