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Dispersion
is the separation of white light into its
component rainbow colors or a gem's ability
to break white light into spectral colors.
The greater the dispersion, the greater
the separation between the spectrum of colors
that are refracted from a gem. The term
"fire" is often used as a synonym
for dispersion.
Fire
in a gem is the result of proper angles
of facets on the gem and the amount
of dispersion of the gem. Dispersion is
what makes a well cut diamond sparkle with
colors or "fire." A prism causes
light to separate into the rainbow spectrum
of colors. A gem with fire also causes light
to separate. The greater the amount of separation,
or the greater a gem's coefficient of dispersion,
the greater a gem's fire.
Rich
color in a gem can sometimes reduce the
effect of dispersion. This is the case of
Benitoite and Demantoid Garnet. Both have
very high dispersion (Benitoite's dispersion
is slightly higher than dimond) but
their strong colors reduce the visual effect
of their high dispersion. Dispersion in
a diamond is moderately high at 0.044, but
Fluorite, for example, shows little or no
fire, with a dispersion of only 0.007.
In
the indexes below, the higher the value,
the greater the fire of the gem. The
numerical value index on the right shows
several gems that have higher dispersion
values than a diamond. This means more fire.
Although the dispersion values may be higher
in these gems, the color saturation of some
of them may mask their high dispersion and
keep their fire from being seen. This is
why a bright white diamond is so highly
prized.
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