Gemstones, Diamonds, & Pearls
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:
- Natural gemstones occur in nature and can be rare and expensive.
- Laboratory-created stones — which also are referred to as synthetic, laboratory-grown, or manufacturer-created — have the same chemical, physical, and visual properties as natural gemstones, but they aren’t as rare and often are less expensive than natural gemstones with similar characteristics.
- Imitation stones look like natural stones, but may be made of glass, plastic, or other less costly material.
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).
Treatments and Enhancements
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:
- if the treatment isn’t permanent
- if the treated stone requires special care
- if the treatment significantly affects the value of the gemstone
Here are some common treatments and their effects:
- Heating can lighten, darken, or change the color of some gemstones, or improve a stone’s clarity.
- Irradiation can add color to colored diamonds, certain other gemstones, and pearls.
- Impregnating some gemstones with colorless oils, wax, or resins hides a variety of imperfections to improve the stones’ clarity and appearance.
- Fracture filling hides cracks in gemstones through an injection of colorless plastic or glass to improve the stones’ appearance and durability.
- Diffusion treatment adds color to the surface of colorless gemstones; the center of the stone remains colorless.
- Dyeing adds color and improves color uniformity in some gemstones and pearls.
- Bleaching lightens and whitens some gemstones, including jade and pearls.
A diamond’s value is based on four criteria:
- Color often is graded on a scale established by the Gemological Institute of America (GIA). On the GIA scales, color is rated from D to Z, with D at the top.
- Cut refers to the quality of how the diamond has been shaped, taking into account the diamond’s proportions, polish, and symmetry.
- Clarity measures the natural imperfections in the stone. On the GIA scales, clarity is rated from flawless to I3. A diamond can be described as “flawless” only if it has no visible surface or internal imperfections when viewed under 10-power magnification by a skilled diamond grader.
- Carat refers to the stone’s weight.
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:
- that the weight is not exact
- the reasonable range of weight for each fraction or the weight tolerance being used
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 made by oysters and other mollusks.
- Cultured pearls also are grown by mollusks, but with human intervention: an irritant introduced into the shells causes a pearl to grow.
- Imitation pearls are man-made with glass, plastic, or organic materials.
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.