Color

When evaluating a gemstone, color is the most critical consideration. Those of the highest quality meet specific criteria in the following areas:
• Hue refers to a gradation or variety of color. Some shades are more rare or desirable, making certain gemstones more costly. Some gemstones have traces of brown or grey, making those a better value for limited budgets.
• Tone refers to intensity of color. For example, the blue in a sapphire may be described as light or dark as a way of conveying the tone of the color. The ideal balance of cost and quality is often somewhere in the middle.
• Saturation refers to the degree of purity of color in a gemstone. A gemstone with excellent saturation has a pure color, with no tinges of grey or brown to decrease its value. Look for a stone with a lot of saturated color.

Clarity

The presence or absence of inclusions, or internal blemishes, determines the degree of clarity in a gemstone. Many kinds of gemstones, including emeralds, rubies, and sapphires, typically have inclusions, and their presence does not lower the value of the stones. The following clarity ratings apply to gemstones:
• Eye clean refers to gemstones in which any inclusions are invisible to the naked eye. These often represent the best values.
• Loupe clean refers to gemstones in which inclusions are almost invisible, even under a 10x magnification.
• Flawless refers to gemstones with few, if any, inclusions. Because they are rare, they command the highest prices.

Rarity

In addition to the 4C’s, gemstone values are influenced by rarity as well as supply and demand. This is why gems that look similar in color and size may greatly differ in price. Within each gem variety, quality determines cost. In general, classic ruby, blue sapphire, and emerald are the most expensive gemstones. Below these are the rare collector’s gems like alexandrite, fancy sapphire and South Sea cultured pearls. The moderate price range includes tanzanite, garnet, tourmaline, aquamarine and Tahitian cultured pearls. The most affordable gemstones include amethyst, citrine, spinel, many colors of garnet, blue topaz, peridot, and freshwater cultured pearls.

Enhancements

Colored gemstones are often treated in some way to enhance their beauty. Untreated gemstones that exhibit good color and clarity are highly unusual and priced accordingly. For most people, a treated gemstone is a more affordable, but still desirable, alternative. The following are typical enhancements today:
• Heat is often used to treat sapphires and rubies to enhance their color. This is a permanent enhancement that requires no special care to maintain.
• Oil, wax, or resin may be added to emeralds to mask inclusions and enhance clarity. Unless resins or hardeners are also added, emeralds treated in this manner may require extra-special care and handling to prevent damage.

Size

Carats are the accepted unit of measurement for gemstones, but the size of a gemstone does not necessarily correspond to its carat weight. Different gemstones have different densities. For example, a ruby and an emerald of the same cut and carat weight will not be exactly the same size. To gauge the size of a gemstone, try judging by the diameter of the stone when viewed from above, rather than the carat weight.

Cut

How a gemstone is cut can have a dramatic impact on appearance, but not necessarily on price. Therefore, it makes sense look at a gemstone's cut to get the most value for the money. Pay attention in the following areas:
• Quality of cut determines how well a gemstone reflects light back to the eye. Look for a gemstone in which color seems to be evenly distributed across the stone, with no dark areas where light is not being reflected.
• Cutting style can also add to the beauty of a gemstone. Sometimes a cut with more facets than a standard cut will cause a particular gemstone to appear to sparkle more brightly.