Sapphire with its Mohs hardness of 9, second only to diamond, is one of the most valuable and wearable of all gemstones. Sapphire is every color of corundum except for red, which is ruby. Famed for its brilliance and rich blue color, sapphire actually occurs in a wide range of colors, including pink, purple, orange, yellow, green and brown. Each color has its own quality variations. In general, the more intense the color and the fewer the distracting zones of unattractive color, the more valuable the stone. Padparadscha sapphire is a very rare sapphire with a pinkish-orange hue. A true padparadscha will always have a hint of pink.
Most natural sapphire is quite pale and light in color. Only a small percentage of natural sapphire exhibits vivid and intense colors without some type of treatment or enhancement, the most common being heat-treatment. With blue sapphire, the intensity of blue is the most important factor. For example, a huge sapphire with a washed-out, weak blue color is much less valuable than a much smaller stone of excellent color. An intense, rich pure cornflower blue that is not too dark or too ‘inky’ is the most desirable colour. Overall, sapphires that are too dark or too light in color are less valuable, but light-blue sapphires often have greater brilliance that is rarely found in darker blue stones. Colorless sapphires are actually quite rare, since most stones will exhibit some faint hints of color.
Sapphire can occur transparent to opaque. The greater the transparency the higher the value. Several types of inclusions are found in sapphires. These include long thin mineral inclusions called needles, mineral crystals, partially healed breaks that look like fingerprints, color zoning, and color banding. Generally, inclusions make a stone less valuable. Price can drop substantially if the inclusions threaten the stone’s durability. Even so, inclusions can actually increase the value of some sapphires. Many of the most valuable Kashmir sapphires contain tiny needle inclusions that give them a velvety appearance. They scatter light, causing the coveted visual effect without negatively affecting the gem’s transparency. Sapphires are generally better clarity than ruby. Blue sapphires with extremely high clarity are rare, and very valuable.
Sapphire Cut and Shape
Sapphires are cut in a wide range of shapes though ovals, cushions, and rounds are most common. Round stones can command very high premiums, especially in diamond-cut calibrated stones weighing 1 carat or more. Cabochons are common for translucent stones or for stones with visible inclusions. Briolettes, beads and tumbled sapphire can also be found, but is usually lower grade material.
The shape of a rough sapphire crystal influences the finished stone’s shape and size. Rough sapphire’s most common crystal form is a barrel- or spindle-shaped hexagonal pyramid. For this reason, finished sapphires are often deep.
To achieve the best overall color, maintain the best proportions, and retain the most weight possible, cutters focus on factors like color zoning, pleochroism, and the lightness or darkness of a stone.
Color zoning—areas of different colors in a stone—is a common sapphire characteristic. Blue sapphire often has angular zones of blue and lighter blue. To accommodate color zoning in some sapphires, cutters orient the concentrated color in a location that offers the best visible color in the cut stone.
In Sri Lankan sapphires, the color is often concentrated close to the surface of the crystal. If a cutter can orient the culet within the concentrated area of color, the stone will appear entirely blue in the face-up position.
Pleochroism is different colors in different crystal directions. Blue sapphires often have greenish blue and violetish blue pleochroism. It’s most desirable to orient the cut so the stone shows the violetish blue color when it is set in jewelry.