The most valuable stones have a deep pigeon's-blood red color.
Although a brilliant stone, it lacks the fire of a diamond and is often cut to enhance the color, even at the expense of weight.
For more than 500 years the finest rubies have come from a small (~400 square mile) area near Mogok, Burma, where they are washed and sieved from limestone gravels. Rubies also occur in the gem gravels of Thailand, Cambodia, Ceylon, and Franklin North Carolina. Burma bright red, strong dichroism, contains "silk" inclusions; Siam is garnet red, less dichroism and no "silk".
Mong Hsu rubies are considered by some to display the best color on the ruby market in more than a decade. The fact that material from this area has been relatively plentiful and responds so satisfactorily to heat treatment has brought the price of good "Burma red" rubies down quite a bit--good news for the consumer.
The stone often referred to as a ruby in the Old Testament and other ancient texts may actually have been a garnet or a spinel. The confusion between these stones has been perpetuated in the names of less valuable gems. The Black Prince's Ruby of the British crown jewels is in fact a spinel.
Since 1902, when Auguste Verneuil developed the flame-fusion process, artificial rubies have been produced from aluminum and chrome oxides. In 1960 an artificial ruby was used in the first working laser.