The following are the basic guide lines to determine the quality and value of a color gems stones:
The 4 Cs
The 4 Cs
In this section we will help you to understand the importance of the color gemstone four Cs, Color, Clarity, Cutting, and Carat Weight. While these factors are well defined for diamonds, no universally accepted system exists for color gemstones.
Color of a gemstone is the first most important factor to determine the value of any gemstone. The more intense the color the higher gemstone value is. This does not mean darker color. The misinformation that darker is better is so strong that these unattractive stones are often selected by uninformed buyers over the stones people think are prettier. Prettier really means better. One example that comes to mind is a dark, inky blue, Sapphire which becomes black when taken out of the strong light environment. This is how you’ll see these gems because you do not walk around with a high intensity light to show others your jewelry gemstone item.
One should always look at color stones in various lighting conditions. Strong light, weak light, day light, and fluorescent light are all common. If possible, you should observe the color stone jewelry item in as many lighting condition as possible. A technical guide to color description is explained in the following tables.
Color of a gemstone is described by jewelers in the gemstone industry by three simple components, Hue, Tone, and Saturation.
The position of a color on a color wheel, i.e., red, orange, yellow, green, blue, and violet. Purple is intermediate between red and violet. White and black are totally lacking in hue, and thus achromatic (without color). Brown is not a hue itself, but covers a range of hues of low saturation, and often high darkness. Classic browns fall in the yellow to orange hues.
The GIA Gemset has 31 (Table 1) Hues which are used to describe virtually all color gemstones. A complete GIA Gemset has 324 sample hue colors with varying Tones and Saturation.
The 4 blue sapphire showing a variation in saturation and tone. The first stone possesses a light tone and low saturation. The second stone is close to ideal in both tone and saturation. The third stone has a greater saturation than the second stone in some area, but its overall tone is too dark and it shows too much extinction. And, the forth stone is so dark in tone that its saturation is reduced. Note that inclusions are far more visible in the stones of light tone than those of dark tones.
The degree of lightness or darkness of a color, as a function of the amount of light absorbed. White would have 0% darkness and black 100%. At their maximum saturation, some colors are naturally darker than others. As an example, a rich violet is darker than even the most highly saturated yellow, while the highest saturation of red and green tend to be similar darkness. The GIA Tone Scale is divided into 11 (Table 2 and 3) grades; 0, being colorless, to 10, being black.
The richness of a color, or the degree to which a color varies from achromaticity. White and black are two achromatic colors, each lacking in hue. When dealing with gems of the same basic hue position, i.e., rubies, which are all basically red in hue, differences in color quality are mainly related to differences in saturation. The stronger red fluorescence of most rubies ( with exception of those from Thai/Cambodian border region) is an added boost to saturation, supercharging it past other gems that lack the effect.
The GIA Saturation Scale is from 1 to 6 (Table 4 and 5). The lower numbers such as 1, 2, and 3 of warm colors such as red, orange, and yellow and tend to look brown and the cool colors such as blue and green tend to look gray. Level 4 does not show either grayishness or brownishness. while neither is strong or weak. Level 5 is strong and level 6 being vivid, almost over colored.