A spectroscope is an optical instrument used to identify gemstones by analyzing how the stone absorbs light. Different elements and impurities in the stone absorb specific wavelengths, creating a unique "fingerprint" in the form of dark lines or bands in a colored spectrum.
Two types of spectroscopes are mainly used for gemological examinations:
Prism spectroscope
Technology: Uses glass prisms to refract the light. Since different wavelengths are refracted differently (dispersion), the light is spread out into a visible spectrum.
Properties: The red region of the spectrum is greatly stretched, making it easier to distinguish and measure specific absorption lines in the red part (e.g. in ruby). However, the blue and violet region is greatly compressed.
Diffraction spectroscope
Technology: Uses a diffraction grating (a very fine-mesh pattern) to disperse the light through the interference of the waves.
Features: Provides a uniform and linear distribution of the entire color spectrum. The spacing between the colors is proportional to the wavelength, making it much easier to view the entire spectrum (from violet to red) at once without having to adjust the instrument.
Why is it used?
The method is non-destructive and is directly crucial for distinguishing natural stones from synthetic ones, or for confirming the cause of color in, for example, sapphires, rubies and emeralds (where chromium, iron or vanadium give characteristic absorption lines).
