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Brilliance/Internal Luster in Gemstones

brilliance in ruby, sapphire, spinel

Brilliance aka Internal Luster is a significant contributor to a gem's beauty and appeal. Observing flashes of brilliance is extremely important.

In those flashes of brilliance is where we see hue, tone and saturation.

Brilliancy also tells us much about how a gemstone is cut. A clean gem that is cut to good proportions will return a large percentage of light to the eye.

A poorly cut gem will normally have large areas of windowing, large areas of extinction, an imbalance or brilliance, no brilliance at all; or all of the above

Brilliance will also suggest how internal characteristics are affecting or diffusing light transmitted through the crystal.

Heavily included gemstones diffuse or block the transmission of light. That makes brilliancy dim and fuzzy. Inclusions often mask large areas of a gem and those areas will not show brilliance. In a gem with limited transparency, the brilliancy areas will be dim.

While watching the flashes of brilliance, consider the following.

  • The true color/hue of the gem can be observed in the patches of light.
  • Saturation and tone are best determined by the patches of light.
  • If the flashes of brilliance are not apparent, the gem is:

    • Not Transparent
    • Excessively included
    • Poorly proportioned
  • The greater the percentage of brilliance, the better is the quality of gem related to finish, transparency, proportion and clarity