How can GIA scientists know if a natural sapphire has received heat treatment? One clue is through its inclusions. Sapphires that formed in metamorphic rock often contain carbon dioxide fluid inclusions or negative crystals. If heat-treated, the carbon dioxide escapes from these inclusions so that they become empty. When the stone and its inclusions are cooled to below 31.5°C, a visible carbon dioxide vapor bubble forms within the liquid. This vapor bubble and the presence of liquid indicate tha

Color-change sapphires are rare gems. Their basic color typically ranges from blue to violet. Under incandescent light, they can appear violetish purple to reddish purple. This phenomenon is caused by trace element impurities in a gem’s atomic structure, which cause it to absorb certain wavelengths of light. Because the wavelength mix varies depending on the light source, the sapphire’s color changes when it’s viewed in different types of light. The strength of the color change is described by g