Diamond Properties : Dispersion

The glinting spectrum or "fire" from a colorless diamond--one of its most prized attributes as a gemstone--results from its excellent dispersion. Dispersion is the separation of white light into its component rainbow colors. The greater the dispersion, the greater the separation between the spectrum of colors that are refracted from a gem.

Diamonds exhibit a high dispersion of visible light. This strong ability to split white light into its component colors is an important aspect of diamond's attraction as a gemstone, giving it impressive prismatic action that results in so-called fire in a well-cut stone.

The refractive index can also be used to describe how visible light can be split into the colors of the spectrum when passing through a transparent substance. Essentially, this happens because the refractive index of a substance is not constant, but rather varies for different wavelengths, or colors, of light. Consequently, the shorter wavelengths of light (the blue end of the spectrum) are bent more than the longer wavelengths (the red) when entering a colorless substance at an angle.

Thus, the colors separate, or disperse, producing the visible spectrum as from a prism. The coefficient of dispersion is a measure of this variation. The greater a substance's coefficient of dispersion, the greater the angular spread of colors from an incoming, inclined beam of white light--a characteristic described as a gem's "brilliance."

The luster of a diamond, a characterization of how light interacts with the surface of a crystal, is brilliant and is described as adamantine, which simply means diamond-like. Some diamonds exhibit fluorescence of various colors under long wave ultraviolet light, but generally show bluish-white, yellowish or greenish fluorescence under X-rays. Some diamonds show no fluorescence.

The high dispersion insures that different wavelengths go in different directions. The colors continually change as the wearer changes the orientation of the diamond in the ambient light. e

Other Properties of Diamond.