A gemstone is defined as a pearl or mineral that has been cut and polished for use as an ornament. We are all attracted to the colors, the shapes and beauty of gemstones. A gemstone’s charm is individual. It can symbolize emotion, follow generational or cultural traditions and represent memories.
Let's clear the air with the terminology separating gemstones into categories of precious and semi-precious. Traditionally the term “precious” was reserved for the finest gemstones. This term implies they are more desired, rare and costly. The term “semi-precious” is referred to all others, regardless of how rare, unusual, difficult to mine or the level of demand they hold.
In this article, there will not be any distinction between semi precious and precious gemstones. All gemstones are beautiful and are graded for value using the same methods. Alexandrite, for example, doesn’t make “the big three” of what is understood to be a “precious” gemstone (ruby, sapphire and emerald). Often alexandrite, for example, will command as much value as those traditionally labeled “precious." All gemstones share three important and desired traits. They are: beauty, rarity and durability.
Everyone has a favorite color, a specific hue that they are attracted to. When speaking of a color in gemstones, we respond instinctively and many times passionately. We are naturally attuned to sensing hue (color) and saturation (depth of color or intensity). Gems in every color have history and a story to tell. We are addressing only the color, referencing only those that are transparent and typically faceted.
The gem’s color is the single most important factor and can command up to 75% of its value. A gem’s color, excluding diamond, is evaluated by a combination of three factors. These are hue, tone and saturation. The hue is the color you first see when you look at the stone. The tone is the percentage of lightness and darkness in the stone and lastly, the saturation is identified as the color’s strength and intensity.
The Gemstone’s Hue
The hue plays a big part in the gemstone’s value. If a gemstone is weak in the color you see (the saturation), it is safe to say this lack of intensity will have a direct effect on the gemstone’s value to the negative.
Below is an illustration of the color wheel used by GIA. The GIA color grading system uses 31 different hues to describe the primary key color of a gemstone. These 31 hues are used to identify and compare the color against the color of the gemstone. The color wheel is a circular diagram of the spectrum used to show the actual color and the relationships between the colors.
The Hue is then modified by tone and saturation...
Saturation is the brightness (purity or intensity) of a hue
A gemstone with excellent saturation reflects a pure color, without any brown or gray hues. The term "intensity" is also used to describe a stone's saturation. Colors of low saturation are sometimes called weak, grayish or brownish while those of high saturation are said to be highly saturated, strong or vivid. The example below shows blue as the hue, but these same levels of color saturation could be applied to any color from the color wheel.
Tone is the lightness or darkness in a gemstone
To describe the darkness or lightness of a colored or colorless stone, the GIA system uses a 0–10 numerical scale with levels of tonal value ranging from "0" which represents totally clear (colorless or white) and "1" which is known as "very very light" or "extremely light," to "10" which is known as "very very dark" to "black." With the exception of hue, each of these parameters by themselves is relatively meaningless, and they must be used in together to tell the full story of a gem's color quality.
The gem's clarity will also affect price
Clarity refers to the relative degree to which a transparent gemstone is free of internal or surface characteristics or imperfections. Internal characteristics are commonly referred to as inclusions and external characteristics are commonly referred to as blemishes in the gem trade. Many are familiar expressing this terminology when describing diamonds. Clarity is also important with all transparent colored stone. Inclusions are not necessarily a negative feature to a gem and can easily determine whether a gem is natural or synthetic. A gem with a lot of inclusions or blemishes will cost less.