The most important factor in the value of a ruby is colour. The top qualities are as red as you can imagine: a saturated pure spectral hue without any overtones of brown or blue. The word red is derived from the Latin word for ruby, ruber, which is derived from similar words in Persian, Hebrew, and Sanskrit. The intensity of colour of a fine ruby is like a glowing coal, probably the most intensely coloured substance our ancestors ever saw. It is no wonder they ascribed magical powers to these fires that burned perpetually and never extinguished themselves.Besides colour, other factors that 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 backlight evenly across the surface without a dark or washed-out area in the centre 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. Rubies and other gemstones are sold per carat, a unit of weight equal to one-fifth of a gram. Larger rubies, because they are more rare, will cost more per carat than smaller stones of the same quality.
The 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 most 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 factors: the intensity and attractiveness of the body colour 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 colour and a sharp prominent star. These gems are valuable and expensive.
The most famous source of fine rubies is Burma, which is now called Myanmar. The ruby mines of Myanmar date back to centuries ago: 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 colour, sometimes 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 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 colour. Burma rubies have a reputation of holding their vivid colour under all lighting conditions.
