Ruby

The name ruby comes from the Latin word ruber, which means “red.”  The glowing red of ruby suggested an inextinguishable flame burning in the stone, even shining through clothing and able to boil water.

Rubies can command the highest per-carat price of any coloured stone. This makes ruby one of the most important gems in the coloured stone market.  In its purest form, the mineral corundum is colourless.  

Trace elements that become part of the mineral’s crystal structure cause variations in its colour.  

Chromium is the trace element that causes ruby’s red colour.

Ruby is one of the most historically significant coloured stones.  Rubies are mentioned four times in the Bible, in association with attributes like beauty and wisdom.  In the ancient language of Sanskrit, ruby is called ratnaraj, or “king of precious stones.”
 
In the first century AD, the Roman scholar Pliny included rubies in his Natural History, describing their hardness and density.  Ancient Hindus believed that those who offered fine rubies to the god Krishna were granted rebirth as emperors.

Quality Factors

Colour

Colour is the most significant factor affecting a ruby’s value: Fine gems are a pure, vibrant red to slightly purplish red.

Clarity

If a ruby's inclusions affect its transparency or brilliance they reduce the gem’s value significantly.

Cut

Rubies are commonly fashioned as mixed cuts, which have brilliant-cut crowns and step-cut pavilions.

Carat Weight

Fine-quality rubies over one carat are very rare and price goes up significantly as size increases.