Most important first
GIA lists characteristics in order of importance to the grade: laser drill-holes first (if present, for disclosure), then the grade-setting inclusions, other inclusions, naturals and extra facets.
Every clarity characteristic GIA defines, placed inside a round brilliant you can turn, and plotted the way a grading report plots them. Then see how size, number, location, relief and nature change a characteristic's effect at 10× magnification.
Clarity is graded face-up by a skilled grader with 10× magnification. Characteristics inside the stone or reaching its surface are inclusions; features on the outside are blemishes.
Same category in other systems
HRD Antwerp names its grades by inclusion size: Loupe Clean, Very Very Small Inclusions, Very Small Inclusions, Small Inclusions, Piqué. GIA does not use the trade term "eye-clean".
Switch characteristics on and off. Tap a name to isolate it, read GIA's definition and see where it sits. The plotting diagram on the right follows GIA's colour code.
GIA reports: red for most inclusions, green for naturals, red and green together for cavities, indented naturals, knots, etch channels and laser drill-holes, black for extra facets. GIA leaves off the plot characteristics that are widespread or faint, or not needed to support the grade or identify the stone (they may appear under Comments). Other blemishes are dashed green here only so you can find them.
GIA bases a clarity grade on the size, number, location, relief and nature of the characteristics. Change one at a time and read how GIA describes its effect. This shows the direction of each effect only; it is not a grading tool.
GIA lists characteristics in order of importance to the grade: laser drill-holes first (if present, for disclosure), then the grade-setting inclusions, other inclusions, naturals and extra facets.
A laser bores a tiny tunnel to a dark inclusion so a bleaching agent can lighten it. Laser drilling is permanent: GIA grades these diamonds and lists drill-holes first among the characteristics.
A glass-like substance is used to fill feathers so they are less visible. GIA does not issue grading reports for diamonds with non-permanent treatments such as fracture filling or coatings; the seller must disclose them.
A blow exactly on a feather or other surface-reaching inclusion can chip the stone; deep feathers can be a durability concern.
Blemishes are surface features that can often be removed by repolishing, so they rarely affect grades lower than IF.
GIA now describes lab-grown diamonds as Premium (clarity Very, Very Slightly Included or higher, plus colour D and Excellent finish) or Standard (minimum Very Slightly Included, colour E–J, Very Good finish) instead of FL–I3 grades.
Sources