UV Light
Using UV light for gemstone identification is based on the fact that minerals absorb invisible ultraviolet radiation and emit visible light. These techniques are very useful for distinguishing natural stones from synthetic or imitation stones.
Shortwave (UV-C) vs. Longwave (UV-A)
Shortwave (about 254 nm): Has higher energy. This light can make some gemstones glow, but it can also be harmful to the eyes and skin. Shortwave is primarily used to detect reactions that distinguish natural stones from synthetic ones. For example, some natural diamonds fluoresce at short wavelengths, which is rarely the case with synthetic diamonds.
Longwave (about 365 nm): Has lower energy and is harmless. This is the wavelength used in regular UV flashlights. It is used to detect basic fluorescence, such as the characteristic red/orange glow of rubies or the blue glow of some diamonds.
Fluorescence vs. Phosphorescence
Fluorescence: The gemstone glows only as long as it is illuminated by the UV light. When the light is turned off, the glow stops immediately. This is used to quickly verify authenticity and type.
Phosphorescence: The gemstone continues to glow (also called afterglow) after the UV light has been turned off. This is very useful for identification because only a few specific gemstones and minerals, such as some synthetic diamonds, have this property.
If you want to test stones at home, it is good to know that natural rubies and some natural diamonds often glow beautifully in UV light.
