This guide defines the five essential characteristics of gemstone quality. By understanding these characteristics, you'll be able to shop with confidence. Print this helpful information and take it with you shopping so you can make the best choice on a beautiful piece of gemstone jewelry.
The jewelry industry recognizes the highest quality gemstones by purity of their hue, the depth of tone, and the color saturation. The best value is in colors that include "slight" traces of other colors, are not too light or dark, and have a lot of saturated color. Nearly all gemstones today have been treated to enhance their color. The most common methods of treatment are heating, nearly always seen with aquamarine, citrine, amethyst, sapphire, ruby and tanzanite, bleaching commonly seen with pearls, and irradiation performed on nearly all blue topaz.
The most valuable gemstones are those that exhibit a pure color and only "slight" hues of other colors in addition to their primary color. Sapphires range in hue from "slightly purplish-blue" to "slightly greenish-blue," pink sapphires always range from "pink" to "slightly purplish-pink," and rubies range from "slightly orangish-red" to "slightly purplish-red". With the exception of opals, variation in a gemstone's hue will be called out in the gemstone details on the product detail page.
Tone represents the depth of color, ranging from colorless to black. Gemstone tone is described as "light," "medium-light," "medium," "medium-dark," and "dark."
Saturation, or color purity, refers to the degree to which the gem is free from brown or gray hues. The most desirable gemstones, which show little gray or brown, are often described as having "vivid" or "strong" color saturation.
Almost all gemstones contain inclusions. Even those most highly prized have at least some inclusions. Flawless gemstones are very rare and very expensive. The best value is found in gems that are lightly to moderately included. Emeralds are typically treated with colorless oil, wax or resin to minimize surface-reaching inclusions.
Because gemstones form under unique circumstances, each individual gemstone is comprised of a combination of trace minerals, which create a unique set of identifying marks or inclusions. Inclusions will not necessarily detract from the beauty or desirability of a colored gemstone.
What to Look For
When considering a colored gemstone's clarity, you should measure your expectations against the standard for that variety of gemstone. Some varieties of colored gemstones, such as aquamarine, blue topaz, and citrine, have naturally fewer inclusions while other gemstones, such as emerald and ruby, tend to have a higher rate of acceptable inclusions.
Clarity is an important factor in comparing quality colored gemstones. Even opaque opals can have milky inclusions that will affect their iridescence and color play. In general, the best values are available in gemstones that are moderately included. Exceptional gemstones with few or no inclusions are available, but they can command extravagant prices.
Colored gemstones are generally cut to maximize the beauty of their color. To recognize quality in the cut of a gemstone, there are several points to consider.
What to Look For
A good cut showcases the gemstone's color, diminishes its inclusions, and exhibits good overall symmetry and proportion. Because gemstone color can vary, there are no hard geometrical standards when it comes to maximizing brilliance or color. Gemstones, especially rarer ones, are sometimes cut for size without regard for their color. For example, when corundum varieties such as sapphire and ruby are cut for maximum weight rather than beauty, they may display banded colors or streaks.
Look at the gemstone in the setting and ensure that all the facets are symmetrical. An asymmetrically-cut crown indicates a gemstone of low-quality. In all cases, a well-cut gemstone is symmetrical and reflects light evenly across the surface, and the polish is smooth, without any nicks or scratches.
The carat weight of a gemstone does not necessarily allow you to accurately envision the size of the gemstone. Different gemstones have different densities (mass per unit volume), so two gems that appear to be the same size may actually have very different weights. For example, a ruby is more dense than a diamond, so a 1-carat ruby will look smaller than a 1-carat diamond.