Generally before they are cut, stones are heated to between 1700 to 1800 degrees Celsius (3100-3300 degrees F) for several hours. The most common treatment for star sapphire is heat treatment.
Many star sapphires will have uneven tops or bottoms, which in many cases is necessary for proper orientation in order to best display asterism.
One should look for an even roundness to the shape. The best cabochons are somewhat transparent to translucent, with smooth domes of good symmetry. Star sapphires are cut en cabochon typically with very high domes to maximize the desirable star effects. The rutile inclusions in star sapphire result in a vitreous to silky luster when cut and polished. Star sapphire owes its desirable asterism to perfectly aligned needle-like rutile inclusions. Some finer specimens may exhibit slight translucency. Thai star sapphire is famed for its golden rayed star. The most desirable color is a vivid, intense blue. Iron and vanadium result in golden to orange tones. A small amount of iron results in more yellow and greenish tones, while chromium produces fine pink to red tones. The coloring agents in blue sapphire are iron and titanium, and vanadium in violet to purple colored stones. Star sapphires can range in color from blue in various tones, to pink, orange, yellow, green, lavender, gray and black. The name 'corundum' comes from the Sanskrit word 'kuruvindam', meaning 'ruby sapphire', while the term 'sapphire' is derived from the Persian word 'safir', which originates from the Greek word for 'blue'.īuying Star Sapphire and Determining Star Sapphire Value Back to Top Star Sapphire Color All corundum has a hardness rating of 9, making it the second hardest material on earth, second only to diamond. Sapphire is a member of the corundum family and is closely related to ruby the red to pink-red gem-quality variety of corundum. Most star sapphire exhibits a white star, but star sapphire from Thailand is famed for its gold colored asterism. Star sapphires can range in color from blue in various tones to pink, orange, yellow, green, lavender, gray or black.
Aligned needles that intersect each other at varying angles produce the rare phenomenon known as asterism.
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