Teardrop-shaped blue sapphire
Gemstone color can be described in terms of hue, saturation, and tone. Hue is commonly understood as the “color” of the gemstone. Saturation refers to the vividness or brightness of the hue, and tone is the lightness to darkness of the hue. Blue sapphire exists in various mixtures of its primary (blue) and secondary hues, various tonal levels (shades) and at various levels of saturation (vividness).
Blue sapphires are evaluated based upon the purity of their primary hue. Purple, violet, and green are the most common secondary hues found in blue sapphires. Violet and purple can contribute to the overall beauty of the color, while green is considered to be distinctly negative. Blue sapphires with up to 15% violet or purple are generally said to be of fine quality. Gray is the normal saturation modifier or mask found in blue sapphires. Gray reduces the saturation or brightness of the hue, and therefore has a distinctly negative effect.
The color of fine blue sapphires may be described as a vivid medium dark violet to purplish blue where the primary blue hue is at least 85% and the secondary hue no more than 15%, without the least admixture of a green secondary hue or a gray mask.
The 423-carat (84.6 g) Logan sapphire in the National Museum of Natural History, in Washington, D.C., is one of the largest faceted gem-quality blue sapphires in existence.
Sapphires of other colors
Sapphires in colors other than blue are called “fancy” or “parti colored” (multi-colored) sapphires.
Fancy sapphires are often found in yellow, orange, green, brown, purple and violet hues.
Multi-colored sapphires are those stones which exhibit two or more colors within a single stone. Australia is the largest source of multi-colored sapphires; they are not commonly used in mainstream jewelry and remain relatively unknown. Multi-colored sapphires cannot be created synthetically and only occur naturally.
Colorless sapphires have historically been used as diamond substitutes in jewelry.
Pink sapphires occur in shades from light to dark pink, and deepen in color as the quantity of chromium increases. The deeper the pink color, the higher their monetary value. In the United States, a minimum color saturation must be met to be called a ruby, otherwise the stone is referred to as a pink sapphire.
More about Sapphires in Part 3.
(Information from Wikipedia, the free encyclopedia)