Diamond Quality Factors
Cut is considered to be the most important of all of the diamond characteristics, as a well-cut diamond will often appear larger than a poorly-cut diamond of the same carat weight, and have the appearance of enhanced color and clarity. The quality of cut is determined by how well the symmetry, polish, and proportions of the diamond produce the most attractive balance of the three different types of reflection. Several proportion factors have the most immediate impact on a diamond’s ability to reflect light correctly. The table size and depth of a diamond relative to the diameter greatly impacts the light return from a diamond. A well-cut diamond is proportioned so that most of the light entering the gem exits back through the top of the stone, perfectly balancing the white light (brilliance) with intense flashes of fire (dispersion). A poorly-cut diamond, with facets cut only a few degrees out of alignment, can result in light exiting through the bottom of the diamond, known as light leakage, instead of from the top where it is visible. This creates a diamond with dulled brilliance from poor light performance within the gem, making the center of the gem look dark.
Color refers to the natural body color of a diamond and not to the reflection of spectral colors that flash when a diamond moves. Most diamonds naturally exhibit slight hints of yellow, brown, or gray. This color is caused by natural trace elements of nitrogen that were present when the diamond formed under the Earth’s crust. The less color a diamond exhibits, the higher the rarity, and therefore the higher the value. Diamonds with less color allow more light to pass, releasing more brilliance and fire. A diamond acts as a prism by dividing light into a spectrum of colors and reflecting this light as colorful flashes called dispersion or fire. Similar to looking through colored glass, color in a diamond will diminish the spectrum of color, or fire, emitted by acting as a filter. A diamond with a higher color grade, i.e., one with less color, demonstrates more colorful fire.
Clarity refers to how clean or clear the diamond is with respect to natural microscopic characteristics that were trapped within or on the diamond while it was forming. Internal characteristics are known as inclusions, and characteristics on the surface of the gem are known as blemishes. Inclusions may be crystals of a foreign material or structural imperfections such as tiny cracks, known as feathers, which can appear whitish or cloudy. Often times the inclusions are microscopic diamonds that were absorbed by the larger crystal before the diamond was carried to the surface of the earth. The quantity, size, color, location, orientation, and visibility of inclusions all affect the final clarity grade of a diamond. Diamonds with no or few inclusions are considered particularly rare and highly valued.
Carat refers to the unique unit of weight measurement used exclusively to weigh gems and diamonds. Carat weight is often confused with visual size even though it is actually a measurement of weight. Depending on the shape and type of gemstone being weighed, the weight will visually show itself differently. For example, a 1.00 ct. round diamond will measure around 6.5mm, and a 1.00 ct. round sapphire will measure around 6.0mm. This is due to the varying density of different gemstones. Total carat weight is a phrase that represents the total weight of all diamonds or other gemstones in a piece of jewelry, when more than one gemstone is used. Diamond solitaire earrings, for example, are usually quoted in total carat weight, indicating the combined weight of the diamonds in both earrings.
Gemstone Quality Factors
Hue refers to the actual body color of the gemstone. It is usually comprised of two parts, the color that has the strongest presence, and any other colors that may be slightly noticeable. Examples include greenish-blue, slightly violet-blue, or violet-pink. In each of these, the modifying color is listed first, with the main color listed second.
Tone is the term used to describe the depth of the color present. For example, if you were to compare a sky blue sapphire to a midnight blue sapphire, you would be able to say that the hue or color is the same but that the tone is different. The sky blue sapphire has “light” tone, and the midnight blue sapphire has “dark” tone.
Saturation is used to describe the purity of the sapphire’s color and whether the gem is exhibiting any gray or brown hues. Gemstones with the highest levels of saturation display the cleanest and truest colors. These are referred to as having “vivid” saturation.
Cut is crucial to bringing out the unique personality of a gemstone. Unlike diamonds, there are no standard “ideal” cuts for gesmstones, as each individual crystal must be custom cut to help the finished gem display the best color and brilliance. Since gemstones come in such a broad variety of colors, each with its own unique properties, there are no specific proportion requirements. Because of this lack of standardization, gemstone cuts are generally not graded by gem laboratories. Instead, jewelers set their own standards for cut and focus on the color of a gesmstone to determine quality. A well-cut gemstone will display the color of the gemstone to its best ability while still enhancing luster and brilliance. Often, gemstones exhibiting a lighter tone of color will be cut deeper to add dimension and intensity to the color. A sapphire of a very dark color will likely be cut shallower to allow more light to reflect within the gemstone, softening and brightening the color. Both methods will enhance a sapphire’s unique beauty. Regardless of the shape of the gemstone, the edges should be symmetrical and even. The facets on the top of the gem, the “crown”, should be even in size, shape, and location. The largest facet on the top of the crown, known as the table, will be symmetrical in shape and well-centered. When the gemstone is rocked and tilted, it should produce bright color flashes as it moves, with no dull spots present.
Clarity in gemstones is viewed in a much different way than it is with diamonds. Most gemstones form in an environment rich with trace minerals that can easily become trapped within the gemstone itself. Some of these might show themselves as small crystals or needle-like inclusions, so it is an accepted fact that most gemstones will have some clarity characteristics or “inclusions.” Because of the depth of color that a gemstone possesses, clarity characteristics are often easily masked and unnoticeable. Gemstones with no inclusions easily viewable with the naked eye are deemed “eye-clean” and offer an excellent value.