Ruby is red corundum, all other color varieties of corundum being referred to as sapphire. The ruby color range includes pinkish, purplish, orangey, and brownish red depending on the chromium and iron content of the stone. The trace mineral content tends to vary with the geologic formation which produced the ruby, so original place designations such as Burmese and Thai have come in later years to be sometimes used in describing color.
Most authorities expect a medium to medium dark color tone in a ruby, naming stones lighter than this, pink sapphire — but there is no general agreement exactly where the line is to be drawn. ."
All corundum gems including ruby have a long history of enhancement. Unless the seller specifically states the stone is unheated, you should assume that some kind of heat treatment has been used. Usually high temperature heating and controlled cooling is done to clarify the stones.
Corundum was first synthesized in the early 1900’s by a simple flame fusion process. Many jewelers and gemologists have had the unpleasant task of telling the proud heir that Grandmother’s treasured ruby ring or brooch contains a flame fusion stone and has a lot more sentimental than commercial value. More complex synthesis processes have been developed in recent years. These so closely simulate natural formation conditions that colors and even inclusions look extremely natural and such stones are difficult for all but the most highly skilled professionals to identify as man-made.
Ruby is hard (9) and tough, making it a superb jewelry stone. (Of course, a heavily included or fractured stone will be less stable.)
