Rubies are often treated to improve their colour and clarity. Common treatments include heat treatment, used to enhance the colour and clarity of the stone, and fracture filling, used to hide cracks and improve clarity.
To determine if a ruby has been treated, gemologists use a variety of tests, including microscopic examination, X-ray diffraction, and spectroscopy. Heat treatment, for example, can cause changes in the crystal structure of the gem, which can be detected through these tests.