Fine rubies are typically sold as being either from Burma or not from Burma. At the epicenter of the world market in two important areas, color and price, Burma rubies hold an unprecedented allure for buyers, despite (or perhaps because of) limited production and a huge reliance on smuggling in order for gems to reach the outside world. The world trade reveres “Burma red,” or “pigeon blood” found in the Mogok valley of Upper Burma as an almost mystical standard. This special appeal determines price. When two rubies of comparable quality are offered for sale, the one from Burma often fetches twice as much. Buyers should ask where a ruby under consideration originated.
A major contributor to the allure of Burma ruby color is fluorescence. Trace amounts of chromium (sometimes less than one percent) are responsible for the red color in rubies. This impurity also causes rubies to fluoresce under ultraviolet light or even sunlight, giving Burmese rubies, which contain more chromium than most others, their appealing red glow. Some Thai rubies may actually be redder than Burma rubies, but lack the same fluorescence.
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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. Blue sapphires with any amount of green as a secondary hue are not considered to be 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.
Padparadscha is a pink-orange corundum, with a low to medium saturation and light tone, originally being mined in Sri Lanka, but also found in deposits in Vietnam and Africa. Padparadscha sapphires are rare; the rarest of all is the totally natural variety, with no sign of treatment.
Fancy Color Sapphire
Yellow and green sapphires are also commonly found. Pink sapphires deepen in color as the quantity of chromium increases. The deeper the pink color the higher their monetary value as long as the color is tending towards the red of rubies. Pink sapphires are a fashion favorite.
Color Change Sapphire
A rare variety of sapphire, known as color change sapphire, exhibits different colors in different light. Color change sapphires are blue in outdoor light and purple under incandescent indoor light; they may also be pink in daylight to greenish under fluorescent light. Some stones shift color well and others only partially, in that some stones go from blue to bluish purple. While color change sapphires come from a variety of locations, the gem gravels of Tanzania is the main source.
A star sapphire is a type of sapphire that exhibits a star-like phenomenon known as asterism; red stones are known as “star rubies”. Star sapphires contain intersecting needle-like inclusions following the underlying crystal structure that cause the appearance of a six-rayed “star”-shaped pattern when viewed with a single overhead light source. The inclusion is often the mineral rutile, a mineral composed primarily of titanium dioxide.
The stones are cut en cabochon, typically with the center of the star near the top of the dome. Twelve-rayed stars are occasionally found, or parallel whisker inclusions can produce a “cat’s eye” effect. The Black Star of Queensland is believed to be the largest star sapphire that has ever been mined, and it weighs 733 carats. The Star of India (weighing 563.4 carats) is thought to be the second-largest star sapphire, and it is currently on display at the American Museum of Natural History in New York City.
The 182-carat Star of Bombay, located in the National Museum of Natural History, in Washington D.C., is an example of a blue star sapphire. The value of a star sapphire, however, depends not only on the weight of the stone but also the body color, visibility and intensity of the asterism.