Absorption spectroscopy reveals which elements or defects cause color by showing which wavelengths of light are absorbed. Infrared spectroscopy detects hydroxyl groups in resins or water in inclusions. Raman spectroscopy identifies molecular structures of fillers or inclusions without destruction.
These techniques help distinguish natural from treated material—for example, detecting flux residues in heated stones or radiation-induced defects. Cryogenic cooling enhances spectral resolution for subtle features. Spectroscopy is non-destructive and central to modern gemological reporting.