The finest rubies are intensely saturated, pure red with no overtones of brown or blue. After color, the factors that influence value are clarity, cut and size. Rubies that are clear with no visible inclusions are more valuable than those with visible internal flaws.

Rubies are readily available in sizes up to 2 carats, and because of their intense color and durability, they make excellent accent stones. Larger sizes can be obtained, but top-quality rubies are rarer and more valuable than colorless diamonds - particularly in sizes above 5 carats. For instance, a 16-carat ruby sold at auction for $227,301 at Sotheby's in 1988. A 27.37-carat Burmese ruby ring sold for $4 million at Sotheby's in Geneva,

Switzerland, in May 1995 - an astounding $146,145 per carat. In contrast, none of the D-color, internally flawless diamonds over 50 carats sold in the last decade can match this value per carat.

Rubies are rarely found perfect in nature - which is why many are heat-treated to intensify or lighten their color or improve their clarity. Heat enhancement is a permanent, stable process. Some rubies also have surface fractures and cavities that are filled with glass-like materials to improve their appearance. This filler may break, fall out or wear out over time if exposed to heat, strong abrasives or constant impact. For both treated or untreated stones, the safest cleaning method is to just use soapy water or a mild commercial solvent and a brush.