Type of break or crack inclusion in a diamond that is irregular, jagged and splintery. A fracture may not follow along a cleavage plane as does a feather, but spreads across the diamond in any other direction.
Four C’s
Four fundamental criteria on which the quality and value of a diamond are judged: cut, colour, clarity, and carat weight. Two additional factors, transparency and the confidence in a diamond grading certificate are also important value factors. Click here to learn more about the C’s of diamond grading.
Fluorescence
Natural characteristic which causes many diamonds to glow under ultra violet light (UV), which is abundant in natural daylight and some artificial lighting. Fluorescence is caused by sub-microscopic structures within the diamond. Diamonds can have various colours of fluorescence, with blue being the most common.
Flawless
Refers to the clarity of a diamond with no inclusions or blemishes. Flawless diamonds are exceptionally rare.
Flat Diamond
Trade term used to describe a diamond with a very shallow crown height and/ or pavilion depth. Flat round brilliant cut diamonds with a shallow pavilion tend to show a fish eye. Flat diamonds lack some brilliance and life.
Flash Effect
Bright, vivid streak of colour found in the glass-like resin filling of diamonds treated by fracture filling.
Fish Eye
Unattractive donut-shaped white ring seen under the table of a round brilliant cut diamond with too shallow a pavilion depth. The ring is caused by the reflection of the diamond’s girdle. Diamonds with a fisheye lack brilliance, and show little life.
Fire
Visible play of colours created by the break-up of light in a diamond. When light enters a diamond, it reflects off of the pavilion facets and refracts, or bends, into a rainbow of colours as it leaves the crown facets. Also known as dispersion.
Finish
Feathers
Type of cleavage inclusion in a diamond with a wispy, feather-like appearance; the feather-like part extends from the origin of the break. Feathers occur along a cleavage plane, or plane of weakness, in a diamond due to directional hardness; they may appear transparent if viewed head on, or bright white if viewed at a 90° angle.