Gold
The word gold, used by itself, means all gold or 24 karat (24K) gold. Because 24K gold is soft, it's usually mixed with other metals to increase its hardness and durability. If a piece of jewelry is not 24 karat gold, the karat quality should accompany any claim that the item is gold.

The karat quality marking tells you what proportion of gold is mixed with the other metals. Fourteen karat (14K) jewelry contains 14 parts of gold, mixed in throughout with 10 parts of base metal. The higher the karat rating, the higher the proportion of gold in the piece of jewelry.

Most jewelry is marked with its karat quality, although marking is not required by law. Solid gold refers to an item made of any karat gold, if the inside of the item is not hollow. The proportion of gold in the piece of jewelry still is determined by the karat mark.

Jewelry can be plated with gold in a variety of ways. Gold plate refers to items that are either mechanically plated, electroplated, or plated by any other means with gold to a base metal. Eventually, gold plating wears away, but how soon will depend on how often the item is worn and how thick the plating is.

Gold-filled, gold overlay and rolled gold plate are terms used to describe jewelry that has a layer of at least 10 karat gold mechanically bonded to a base metal. If the jewelry is marked with one of these terms, the term or abbreviation should follow the karat quality of the gold used (for example, 14K Gold Overlay or 12K RGP). If the layer of karat gold is less than 1/20th of the total weight of the item, any marking must state the actual percentage of karat gold, such as 1/40 14K Gold Overlay.

Gold electroplate describes jewelry that has a layer (at least .175 microns thick) of a minimum of 10 karat gold deposited on a base metal by an electrolytic process. The terms gold flashed or gold washed describe products that have an extremely thin electroplating of gold (less than .175 microns thick). This will wear away more quickly than gold plate, gold-filled or gold electroplate.

Gemstones
Natural gemstones are found in nature. Laboratory-created stones, as the name implies, are made in a laboratory. These stones, which also are referred to as laboratory-grown, [name of manufacturer]-created, or synthetic, have essentially the same chemical, physical and visual properties as natural gemstones. Laboratory- created stones do not have the rarity of naturally colored stones and they are less expensive than naturally mined stones. By contrast, imitation stones look like natural stones in appearance only, and may be glass, plastic, or less costly stones. 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 (1/5th) 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 is expressed in millimeters (for example, 7x5 millimeters).

Gemstone treatments or enhancements refer to the way some gems are treated to improve their appearance or durability, or even change their color. Many gemstones are treated in some way. The effects of some treatments may lessen or change over time and some treated stones may require special care. Some enhancements also affect the value of a stone, when measured against a comparable untreated stone.

Jewelers should tell you whether the gemstone you're considering has been treated when: the treatment is not permanent; the treated stone requires special care; or the treatment significantly affects the value of the gemstone.

Some common treatments that you may be told about and their effects include:

1. Heating can lighten, darken or change the color of some gems, or improve a gemstone's clarity.
2. Irradiation can add more color to colored diamonds, certain other gemstones and pearls.
3. Impregnating some gems with colorless oils, wax or resins makes a variety of imperfections less visible and can improve the gemstones' clarity and appearance.
4. Fracture filling hides cracks or fractures in gems by injecting colorless plastic or glass into the cracks and improves the gemstones' appearance and durability.
5. Diffusion treatment adds color to the surface of colorless gems; the center of the stone remains colorless.
6. Dyeing adds color and improves color uniformity in some gemstones and pearls.
7. Bleaching lightens and whitens some gems, including jade and pearls.

Diamonds
A diamond's value is based on four criteria: color, cut, clarity, and carat. The clarity and color of a diamond usually are graded. However, scales are not uniform: a clarity grade of "slightly included" may represent a different grade on one grading system versus another, depending on the terms used in the scale. Make sure you know how a particular scale and grade represent the color or clarity of the diamond you're considering. 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.

As with other gems, diamond weight usually is stated in carats. Diamond weight 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 - .304 carat. Some retailers describe diamond weight in fractions and use the fraction to represent a range of weights. For example, a diamond described as 1/2 carat could weigh between .47 - .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, and the reasonable range of weight for each fraction or the weight tolerance being used.

Some diamonds may be treated to improve their appearance in similar ways as other gemstones. Since these treatments improve the clarity of the diamond, some jewelers refer to them as clarity enhancement. One type of treatment - fracture filling - 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.

Another treatment - lasering - 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 then forced through a tiny tunnel made by the laser beam to remove the inclusion. Lasering is permanent and a laser-drilled stone 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 and therefore more valuable. 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 are much less costly. Certain laboratory-created gemstones, such as lab-created moissanite, also 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 other lab-created stones.