Before you buy gemstones, diamonds, or pearls, it’s a good idea to learn about them so you can recognize differences that might affect their value. For example, the value of gemstones can be affected by their size, whether the stones are natural or lab-created, and whether they have undergone treatments to enhance them.
There are three primary types of gemstone products:
Laboratory-created and imitation stones should be clearly identified as such.
Gemstones may be measured by weight, size, or both. The basic unit for weighing gemstones is the carat, which is equal to one-fifth of a gram. Carats are divided into 100 units, called points. For example, a half-carat gemstone would weigh .50 carats or 50 points. When gemstones are measured by dimensions, the size often is expressed in millimeters (for example, 7x5 millimeters).
Gemstone treatments or enhancements refer to the way some stones are treated to improve their appearance or durability, or even change their color. The effects of some treatments may lessen or change over time, and some treated stones may require special care. Some enhancements affect the value of a stone when measured against a comparable untreated stone.
A jeweler should tell you whether the gemstone you’re looking at has been treated:
Here are some common treatments and their effects:
A diamond’s value is based on four criteria:
Diamond weight usually is stated in carats and may be described in decimal or fractional parts of a carat. If the weight is given in decimal parts of a carat, the figure should be accurate to the last decimal place. For example, ”.30 carat” could represent a diamond that weighs between .295 and .304 carat. Some retailers describe diamond weight in fractions, using the fraction to represent a range of weights. A diamond described as 1/2 carat could weigh between .47 and .54 carat. If diamond weight is stated as fractional parts of a carat, the retailer should disclose two things:
Some diamonds, like other gemstones, may be treated to improve their appearance. Since these treatments improve the clarity of the diamond, some jewelers refer to them as clarity enhancement.
Fracture filling, for example, conceals cracks in diamonds by filling them with a foreign substance. This filling may not be permanent, and jewelers should tell you if the diamond you’re considering has been fracture-filled.
Lasering is a treatment that involves the use of a laser beam to improve the appearance of diamonds that have black inclusions or spots. A laser beam is aimed at the inclusion; acid is forced through the tiny tunnel made by the laser beam to remove the inclusion. Lasering is permanent, and a laser-drilled stone usually does not require special care. While a laser-drilled diamond may appear as beautiful as a comparable untreated stone, it may not be as valuable. That’s because an untreated stone of the same quality is rarer. Jewelers should tell you whether the diamond you’re considering has been laser-drilled.
Imitation diamonds, such as cubic zirconia, resemble diamonds in appearance but cost much less. Certain laboratory-created gemstones like moissanite resemble diamonds and may not be adequately detected by the instruments originally used to identify cubic zirconia. Ask your jeweler if he has the current testing equipment to distinguish between diamonds and lab-created stones.
Pearls can be natural, cultured, or imitation.
Natural pearls are very rare, so most pearls used in jewelry are either cultured or imitation pearls. Cultured pearls usually are more expensive than imitation pearls. A cultured pearl’s value generally is based on its size, usually stated in millimeters, and the quality of its nacre coating, which gives it luster. Jewelers should tell you if the pearls are cultured or imitation.
Some pearls occur naturally in black, bronze, gold, purple, blue, and orange tints; others are dyed. Jewelers should tell you whether the colored pearls are naturally colored, dyed, or irradiated.