Color
Jewelers describe the color of a gemstone in terms of three characteristics: hue, saturation, and tone. A gemstone's basic color is its hue, and those with purer hues (for emeralds, green; for sapphires, blue; and for rubies, red) are generally considered more valuable. Often, however, a hint of another color can be detected. Saturation is a measure of the intensity or purity of a gem's hue and is determined by the degree to which gray or brown hues mute its defining color. Value tends to increase with saturation, so a fully saturated purplish blue sapphire may well be more expensive than a muted pure blue one. The tone of a gemstone, a measurement of its lightness or darkness, is usually given as light, medium-light, medium, medium-dark, or dark.
Clarity
A flawless gemstone is rare and expensive. As with diamonds, most gemstones have inclusions, or tiny mineral flaws, that can be seen under magnification or by the careful eye. Make sure that any inclusions in the stone do not penetrate deeply into the gem, as this may cause it to break or crack. Clarity grades range from VVS (very, very slightly included) to I3, in which inclusions are prominent and severely affect the gemstone's beauty.
