Dark-field illumination: A method of illuminating diamonds and other gemstones with a strong light from the side while the stone is being viewed against a black background. It causes some inclusions and imperfections to stand out clearly.
dark-field illumination The trademarked GemoLite microscope by GIA, uses bright circular light with the dark-field in the background to view diamonds and gemstones under magnification.
illumination technique which makes it possible to examine diamonds and other gemstones free, to a large extent, from reflections, and without 'the need to clamp stones individually; as is the case with traditional dark-field illumination.
a diamond without external or internal flaws or blemishes of any description when viewed by a trained eye under efficient illumination and under a corrected magnifier of not less than ten power; binocular magnification under dark-field illumination ...
 See also: Gemstones, Crown, Clarity, Shape, Girdle
  
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