Sapphire Color
Blue is the best-known of the sapphire colors. The prized Kashmir and Burmese sapphires have a deep blue that is intense and velvety. These sapphires are not often seen on the market today. Sri Lankan and Madagascar sapphires are the most common today, with a wide range of colors from light blue to dark blue. 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 colors are best viewed under natural daylight. In artificial or incandescent light, sapphire colors can appear darker and inky black-blue. Many may even appear redder and less attractive than they really are. Sapphire colors are a result of trace impurities. The coloring agents found in blue sapphire are typically iron and titanium. Violet stones are colored by vanadium. Pink sapphire and purple sapphire are often colored by iron and titanium impurities. Most yellow sapphire is naturally on the lighter side. It is through heat treatment that a more intense yellow golden color is produced. Beryllium-treated sapphire may result in brilliant bright yellow. Small traces of iron can cause yellowish and greenish hues in stones. Chromium is known to produce fine pinks (and red in ruby), whilst iron and vanadium together can produce lovely orange stones. Padparadscha sapphire is a very rare sapphire with a pinkish-orange hue. A true padparadscha will always have a hint of pink. Many 'green' sapphires consist of fine alternating bands of blue and yellow sapphire, which are visible under a microscope.
Sapphire Clarity and Luster
Sapphire can occur transparent to opaque. Transparent materials are the most valuable. Some translucent materials are cut into beads or cabochons. Opaque materials have very little gemstone value, although they may sometimes be used for ornamental carving. Sapphires are generally cleaner than ruby, so it is best to look for stones that are eye-clean. Eye-clean stones in larger sizes are quite rare, especially in ideal colors. In some cases, extremely fine silk throughout the stone can enhance the value of some sapphires. The famous sapphires from Kashmir have a velvety blue color which is caused by this fine silk. This same silk causes the asterism seen in star sapphires. However, too much silk weakens the color, rendering it an undesirable grayish colour. The rutile needles that are responsible for the silky shine reflect the light in sixty-degree angles. If the rutile needles are perfectly aligned in the same direction, the inclusions can result in six-rayed asterism when cut en cabochon and viewed under strong light. Sapphire exhibits an attractive vitreous luster.
Sapphire Cut and Shape
Various shapes and cutting styles are common with sapphires. Ovals, cushions, and rounds are commonly seen, as are other shapes, such as fancy hearts, pears and emerald cuts. 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.
Sapphire Treatment
The most common treatment for sapphire is heat treatment, though unheated specimens can be found. Stones are heated (generally before they are cut) to between 1700 to 1800 degrees Celsius (3100-3300 degrees F) for several hours. Most sapphires today are heated, and unheated stones in rich blue can command enormous prices in today's market. Some blue sapphires may also be diffusion treated, though this treatment is more common for star sapphires. Beryllium treatment is now being used to produce stunning orange and red colors that were once rarely seen. All sapphire treatments should be fully disclosed by any reputable dealer.
