A spectroscope is a gem-testing instrument that spreads light from a stone into a spectrum. Dark lines and bands show where the stone absorbs.
In more detail
A prism or a diffraction grating does the spreading. A grating spreads wavelengths evenly. A prism squeezes the red end and stretches the violet end. The lines often name the coloring element, not the stone.
How we measure it
Our Spectroscope computes the spectrum from measured spectra on a 1 nm grid, through 1 to 10 mm. You choose lamp light (illuminant A) or daylight (D65). Its prism is a 60° prism of N-SF11 flint glass. It is a teaching model, not a test of a real stone.
Related terms
- Absorption spectrum: An absorption spectrum shows which wavelengths of light a stone absorbs. In a spectroscope, the absorbed parts of the spectrum look dark.
- Absorption line: An absorption line is a narrow dark line in a spectrum, where a stone absorbs a narrow range of wavelengths. An absorption band is a broad dark stretch where it absorbs a wide range.
- Dispersion: Dispersion is how differently a stone bends red and violet light. Gemologists give it as the index difference between the B line (686.7 nm) and the G line (430.8 nm).
- CIE colorimetry: CIE colorimetry turns a light spectrum into a color by weighting it with standard human color-matching functions. Standard illuminants, such as D65 (daylight) and A (incandescent lamp, 2856 K), define the light.