Unusual Optical Effect in Blue Sapphire
It should be noted that the UV lamp in the DiamondView has a wavelength less than 225 nm (according to the user’s manual). The energy of UV radiation is considered too weak for the color treatment of corundum (see K. Nassau, Gemstone Enhancement, Butterworth-Heinemann, 1984, p. 221). In this sapphire, the DiamondView apparently caused the color change. Such a reversible change of color with exposure to light is called photochromism.