Symmetry refers to how well the facets of a diamond are aligned. The symmetry of a diamond is controlled by the manufacturing process when cutting the diamond.
Symmetry imperfections can occur either unintentionally through errors in the cutting process or internationally in order to prevent the natural inclusions in the diamond from showing in the finished diamond.
The Symmetry or exactness of the diamond’s outline, and the shape, placement, and alignment of its facets, accessed on a scale ranging from Excellent to Poor.
Excellent: No symmetry flaw to minute symmetry flaws that can be viewed with difficulty at 10X magnification.
Very Good: Minor symmetry flaws are seen at 10X magnification.
Good: Noticeable symmetry glaws are seen at 10X magnification. The diamond’s overall appearance may be affected.
Fair: Obvious symmetry features are seen at 10X magnification. The diamond’s overall appearance is often affected.
Poor: Prominent symmetry features are seen at 10X magnification. The diamond’s overall appearance is significantly affected.
Examples of Symmetry Flaws
Out of Round
Deviation from the circular shape
Deviation of table from the central position
Deviation of the culet from the central position
Displacement of the table facet and culet in different directions
Crown Angle Variation
Unequal crown angles
Pavilion Angle Variation
Unequal pavilion angles
Girdle Thickness Variation
Variation of the girdle thickness at the bezel-main positions
Displacement of the crown and pavilion facets
Hearts and Arrows
The famous Hearts and Arrows effect in a diamond occurs when a diamond is cut to specific or ideal proportions with excellent optical symmetry.
The Hearts and Arrows pattern can be seen through special light-directing viewing equipment such as the Idealscope and ASET Scope. It is defined as the visual pattern of eight symmetrical arrows when viewed from the crown (face-up position) and eight symmetrical hearts when viewed from the pavilion (table-down position).
After a diamond is cut, it has to be polished to achieve a smooth surface. This polishing is usually done with a polishing wheel. Diamond polishing is an extremely difficult skill as the cutter has to achieve the best possible polish without polishing down too much of the diamond.
Unlike inclusions which occurs naturally that affect the Clarity grade, polish marks can caused by human errors during the polishing process. It is however, nearly impossible to achieve a flawless polish.
GIA examines the diamond under 10x magnification looking for the imperfections or polish marks that the diamond cutter may have left behind.
The polish or smoothness of the diamond’s surface is assessed on a scale ranging from Excellent to Poor.
Excellent: No polish or only few minute polish features that can be viewed with difficulty at 10X magnification.
Very Good: Minor polish features visible at 10X magnification.
Good: Noticeable polish features at 10X magnification.
Fair: Obvious heavy polish features are seen face-up at 10X magnification and may be visible to the naked eye.
Poor: Prominent heavy polish features are visible to the naked eye
Examples of Polish Marks
A small notch on a facet or girdle junction.
A small opening in the surface, usually due to inclusions falling out during polishing.
A bumpy looking texture.
Laser Manufacturing Remnant
appears as a transparent or white groove.
A whitish haze on a diamond’s surface, caused by high temperatures from a polishing wheel.
A collection of nicks at facet junctions.
A transparent-looking white line on the diamond’s surface.
A girdle that has been left unpolished.
Fluorescence is the visible light some diamonds emit when they are exposed to invisible ultraviolet (UV) rays.
The fluorescence rating in the GIA report refers to the intensity of the diamond’s reaction to the UV rays and ranges from None to Very Strong.
During the diamond’s composition in the earth, different elements such as nitrogen, boron and aluminium may be absorbed. The fluorescence from the diamonds are the result of such elemental inclusions.
Blue is by far the most common colour of diamond fluorescence. More that 95% of the diamonds that exhibit fluorescence exhibits blue.
The variety of other colours that diamonds can fluorescence in includes yellow, yellow, orange, red, white and green.
The variations in the atomic structure, such as the number of nitrogen atoms present in the diamond are what that causes the phenomenon.
Fluorescence is present in approximately 25% – 35% of all diamonds. The fluorescence in a diamond is however, not noticeable unless under UV lighting and only 10% of all the diamonds that have fluorescence will have strong enough fluorescence to cause a change in appearance under UV lighting.
The effect that fluorescence have on the allure and beauty of the diamond is highly negligible and should not be a major factor when selecting your diamond.
Having said that, it is still possible though super rare to find a hazy and oily looking diamond caused by the presence of fluorescence (0.2% of fluorescence diamonds).