From The Gemology Project
Revision as of 07:14, 8 September 2006 by Doos (talk | contribs) (Absorption)
Jump to: navigation, search
Exlamation mark.jpg
This section is currently under construction, do not edit until this message is gone
Doos 03:37, 28 July 2006 (PDT)

The spectroscope is a tool to examin which parts of white light are absorbed by a gemstone (as well as in other materials).
Materials can absorb parts of the electromagnetic spectrum and when the absorbed parts fall with in the visible range, that absorbed part will influence the color of the material.
When a gemstone is observed with a spectroscope, the absorbed parts show as dark lines and/or bands in the spectroscope image.

OPL teaching diffraction grating spectroscope on stand (left) and prism spectroscope with adjustable slit (right)

There are two types of spectroscopes used in gemology:

  1. Prism spectroscopes (based on dispersion)
  2. Diffraction grating spectroscopes (based on diffraction)



Color as perceived by the human eye concists of the 7 colors of the rainbow: Red, Orange, Yellow, Green, Blue, Indigo and Violet. All these colors travel at different speeds and have their own wavelengths. When all the above colors combine, we see it as white light.

When white light reaches a substance, part of the light components may be absorbed by the substance, the other components (residu) form the color of that substance. For instance if a gemstone would absorb all the colors of the rainbow except red, only the red part of the original white light will be visible and the gemstone will therefor be red.
When viewed through a spectroscope, the absorbed parts will disappear from the spectrum image and only red will be visible in the prism of the spectroscope.
Likewise if all colors except red and blue are obsorbed by a gemstone, the residual colors (red and blue) will give rise to a purple gemstone.

The pictures below give a crude example of both above mentiond situations.

absorption of all wavelengths except red
absorption of all wavelengths except red and blue

Of course in real life the spectrum images are much more sophisticated with small lines and bands indicating specific absorption parts of white light.
The energy from the absorbed colors (or better "wavelengths") is transformed inside the gemstone into other types of energy, mostly heat.

One should concider color as a form of energy traveling at a specific wavelength.

Types of spectroscopes

Diffraction grating spectroscope

diffraction grating spectrum

diffraction grating spectrum with scale in nm

Prism spectroscope

prism spectrum

prism spectrum with scale in nm

Related topics