A Guide to Buying Ruby

Ruby is the variety of corundum with a red color. Other colors are referred to as sapphire, although there is some disagreement about whether a light pink stone is considered ruby or pink sapphire. In Asia any red corundum including pink is considered ruby, outside of Asia it is termed pink sapphire. Ruby was most likely discovered in Sri Lanka (Ceylon), although the most known source is the Mogok Stone Tract in Burma. It has also been found in Afghanistan, Kenya, Pakistan, Tanzania, along the Thai/Cambodian border, Vietnam, and Yunnan (China). The name is believed to be derived from the Latin word for red, “ruber.”

The primary factor in determining the value of a ruby is its color. The ideal color would be similar to a red traffic light, sort of an intense rich crimson. A stone that is too light or too dark will have much less value. They are best viewed either in daylight or incandescent light, as these sources have the most output in the red end of the spectrum. Fluorescent light will have a tendency to make the stones appear grayish.  

Rubies tend to be less clean than sapphire in terms of clarity, so stones that appear clean to the unaided eye are acceptable. There are other cases where the inclusions such as extremely fine silk will increase the value of the stone, star rubies are a good example. Too much silk however can detract from the color of the stone making the star appear grayish which is undesirable. Fine star rubies have sharp six or twelve rayed stars that should be centered well in the middle of the cabochon. The legs should be smooth and the stone should still have an intense red color. Having a good star alone isn’t enough to be considered highly valuable.

Ovals and cushions are the most common cut for rubies, although they can be found in other shapes including emerald, heart and round. Round rubies are worth slightly more than the other shapes, pears and marquises slightly less. In any shape they shouldn’t be cut overly shallow or deep. Cabochons can also be found but usually only in star rubies or when the clarity isn’t good enough to facet.

Most rubies you will find are heat treated to improve their appearance; this helps them become stable in color. Many are also heated near flux to heal their fractures. Occasionally you will also see stones treated with dying, oiling, or surface diffusion. In smaller stones of lesser quality heat treated stones sell for the same amount as untreated stones, but in larger stones of finer quality an untreated stone can sell for 50% or more than a comparable treated stone. Synthetic rubies also exist and sell for just pennies per carat. 

Large quality rubies are much rarer than large sapphires of the same quality. An untreated ruby larger than 2 carats is rare, over 5 carats is considered world-class. Other than imperial jadeite and certain rare colors of diamond, ruby is considered to be the world’s most expensive gem. The highest price ever paid for a ruby was $3.6 million ($425,000/carat) for an 8.62 carat ruby set in a Bulgari ring, which occurred on February 15, 2006.

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