The very finest, top quality ruby is so rare that it has been the world’s most valued gemstone for thousands of years. In fact, even today, flawless top quality rubies are more valuable and rare than top quality colorless diamonds. A 16 carat ruby sold at auction for US$227,301 per carat at Sotheby’s in 1988 F95zone. A 27.37 carat Burmese ruby ring sold for US$4 million at Sotheby’s in Geneva in May 1995, or $146,145 per carat. A 32 carat ruby sold for US$144,000 per carat at Sotheby’s in 1989. In contrast, eight D-color internally flawless diamonds over 50 carats were sold in the past 9 years and the largest, a pear-shape of 102 carats, fetched a mere US$125,000 per carat. Top rubies are so rare even the world’s top gem dealers must incessantly comb through wealthy estate sales and auctions to find them. Clean bright stones in sizes above five carats are particularly rare.
Ruby is the gem quality form of the mineral corundum, and one of the most durable minerals which exists, a crystalline form of aluminum oxide. Corundum has a hardness of 9 on the Mohs scale and is also extremely tough. In its common form, corundum is even used as an abrasive. Colors of Corundum other than red are known as Sapphire. The element Chromium is responsible for the red color of this gem, but too much Chromium can actually turn corundum emerald green in color. Heat treatment is very common in ruby gemstones (as is true for all forms of corundum) and is used to dissolve “silk” inclusions, which results in a more transparent, more intensely colored stone. The heat treatment is considered permanent and does not usually detract from the value of the stone.
The most famous source of fine rubies is Burma, which is now called Myanmar. The ruby mines of Myanmar are older than history: stone age and bronze age mining tools have been found in the mining area of Mogok. Rubies from the legendary mines in Mogok often have a pure red color, which is often described as “pigeon’s-blood” although that term is more fanciful than an actual practical standard in the trade today. Myanmar also produces intense pinkish red rubies which are also vivid and extremely beautiful. Many of the rubies from Burma have a strong fluorescence when exposed to ultraviolet rays like those in sunlight, which layers on extra color. Burma rubies have a reputation of holding their vivid color under all lighting conditions.
Fine rubies are also found in Thailand. Thai rubies tend to be darker red in tone: a real red, tending toward burgundy rather than pink, as Burma rubies do. This makes them very popular in the United States where consumers generally prefer their rubies to be a darker red rather than a darker pink. Some Thai rubies have black reflections, a phenomenon called extinction, which can make their color look darker than it really is. But Thai rubies can also have a rich vivid red that rivals the Burmese in intensity. Sri Lankan rubies can also be very beautiful. Many Sri Lankan stones are often pinkish in hue and many are pastel in tone. Some, however, resemble the vivid pinkish red hues from Burma.
Rubies from Kenya and Tanzania surprised the world when they were discovered in the sixties because their color rivals the world’s best. Unfortunately, most of the ruby production from these countries has many inclusions, tiny flaws which diminish transparency. Rubies from the African mines are rarely transparent enough to facet. However, their fantastic color is displayed to full advantage when cut cabochon style. A few rare clean stones have been seen which are top quality.
The most important factor in the value of a ruby is color. The top qualities are as red as you can imagine: a saturated pure spectral hue without any overtones of brown or blue. An intense pure, red color, uniform color is the most valuable gem. Clarity is also of secondary importance, but a fine colored gem with slight flaws is still highly valued. Large sizes rubies are more rare than diamond and a value of fine gem ruby increases significantly (more so than other gems) with increased weight.
The word red is derived from the Latin for ruby, ruber, which is derived from similar words in Persian, Hebrew, and Sanskrit. The intensity of color of a fine ruby is like a glowing coal, probably the most intensely colored substance our ancestors ever saw. It is no wonder they ascribed magical powers to these fires that burned perpetually and never extinguished themselves.
After color, the other factors which influence the value of a ruby are clarity, cut, and size. Rubies that are perfectly transparent, with no tiny flaws, are more valuable than those with inclusions which are visible to the eye. Cut can make a big difference in how attractive and lively a ruby appears to the eye. A well-cut stone should reflect back light evenly across the surface without a dark or washed-out area in the center that can result from a stone that is too deep or shallow. The shape should also be symmetrical and there should not be any nicks or scratches in the polish.
Ruby sometimes displays a three-ray, six-point star. These star rubies are cut in a smooth domed cabochon cut to display the effect. The star is best visible when illuminated with a single light source: it moves across the stone as the light moves. This effect, called asterism, is caused by light reflecting off tiny rutile needles, called “silk,” which are oriented along the crystal faces. The value of star rubies and sapphires are influenced by two things: the intensity and attractiveness of the body color and the strength and sharpness of the star. All six legs should be straight and equally prominent. Star rubies rarely have the combination of a fine translucent or transparent color and a sharp prominent star. These gems are valuable and expensive.