Diamond Polish and Symmetry: Guide to GIA Terminology and Abbreviations
Polish FeaturesPolish is graded on a scale from Excellent to Poor based on the presence and visibility of polish features at 10x magnification. The following features are considered in the polish assessment.
|Abrasion||Abr||An area of minute scratches or pits along a facet edge producing a fuzzy white line instead of a sharp facet junction|
|Whitish haze caused by excessive heat during polishing or, occasionally, by a jeweller’s torch is listed as “Brn”.
A burn mark caused by excessive heat at the location where the dop touched the diamond is referred to more specifically as “Dop”.
|Laser Manufacturing Remnant||LMR||A remnant of laser manufacturing that remains on the surface of the polished diamond; typically appears as a transparent or white groove; only considered polish when it does not penetrate into the diamond at 10x magnification.|
|Lizard Skin||LS||A transparent, uneven texture confined to one facet caused by polishing a facet off-grain|
|Nick||Nck||A small notch on a facet junction, usually along the girdle or at the culet|
|Pit||Pit||A tiny opening appearing as a white dot|
|Rough Girdle||RG||An irregularly pitted or granular surface of a bruted girdle due to pits and nicks|
|Scratch||Scr||A surface mark, normally seen as a fine white line that may be curved or straight|
|Parallel lines left by the polishing process; may appear white (Wht) or transparent (TP). A heavy transparent polish line off a surface-reaching feature is referred to more specifically as a "drag line".
A surface feature made during the polishing process that resembles an extra facet without a distinct or straight facet junction is referred to as a "polish mark".
Polish Feature LocationsThe location of each polish feature is specified using the following terms.
|Crown Corner Step Facet||crown corner step|
|Crown Facet||crown facet|
|Crown Step Facet||crown step|
|Lower Half Facet||l.h.|
|Pavilion Main Facet||main|
|Pavilion Corner Step Facet||pav corner step|
|Pavilion Facet||pav facet|
|Pavilion Step Facet||pav step|
|Upper Half Facet||u.h.|
Symmetry is graded on a scale from Excellent to Poor based on the presence and visibility of symmetry deviations at 10x magnification. The following features are considered in the symmetry assessment.
|Crown Angle Variation||CV||Unequal crown angles|
|Crown Height Variation||CHV||Girdle plane not parallel to the table causing uneven crown height|
|Culet Off-Centre||C/oc||Deviation of the culet from the central position on the pavilion|
|Extra Facet||EF||Additional facet placed without regard for symmetry and not required by the cutting style|
|Girdle Thickness Variation||GTV||Variation of the girdle thickness at the bezel-main positions|
|Lower Half Percentage
|LPV||Variation of lower half facet length percentages|
|Lower Half Variation||LHV||Unequal lower half facet angles|
|Misalignment||Aln||Displacement of the crown and pavilion facets in relation to each other|
|Difference in shape or size between one facet and another of the same type, or distortion of a given facet; bezel, star and main facets that are misshapen are listed more specifically as misshapen bezel (MB), misshapen star (MS) and misshapen main (MM)|
|Missing Facet||MF||Asymmetrically missing facet|
|Natural||N||Part of the original rough diamond’s surface that remains on the polished diamond|
|The table of a Round Brilliant is not a regular octagon, showing differences among the four table sizes (T/oct) or among the eight table edges (TEV)||
|Fully formed facet that does not reach its prescribed location (short facet) or is incompletely finished (open facet), resulting in adjoining facets not meeting at precise points; non-pointing of bezel and main facets are listed more specifically as short main (SM), short bezel (SB), open main (OM) and open bezel (OB)|
|Out-of-Round||OR||Deviation from the circular shape of a round diamond|
|Pavilion Depth Variation||PDV||Variation of pavilion depth|
|Pavilion Angle Variation||PV||Unequal pavilion angles|
|Star Percentage Variation||SPV||Variation of star facet length percentages|
|Star Angle Variation||SV||Unequal star facet angles|
|Table Off-Centre||T/oc||Deviation of the table from the central position on the crown|
|Table/Culet Alignment||T/C||Displacement of the table facet and culet in different directions|
|Upper Half Variation||UHV||Unequal upper half facet angles|
|Uneven Outline||UO||Asymmetrical shape outline; also refers to bumps and flattened areas created by a natural, extra facet or uneven girdle faceting on round diamonds|
Cumulative is listed under symmetry features when the symmetry grade is based on the combined effect of symmetry features instead of individual deviations. For example, a diamond with pavilion depth variation (PDV) and crown angle variation (CV) that measures on the border of Very Good and Good may receive a lower symmetry grade based on their combined appearance and be represented as “Cumulative: PDV, CV”.
|LMR||Laser Manufacturing Remnant|
|Wht||White Polish lines|
|TP||Transparent Polish Lines|
|CV||Crown Angle Variation|
|CHV||Crown Height Variation|
|GTV||Girdle Thickness Variation|
|LHV||Lower Half Angle Variation|
|LPV||Lower Half Percentage Variation|
|PDV||Pavilion Depth Variation|
|PV||Pavilion Angle Variation|
|SPV||Start Percentage Variation|
|SV||Star Angle Variation|
|TEV||Table Edge Variation|
|UHV||Upper Half Angle Variation|
|crown corner step||Crown Corner Step Facet|
|crown facet||Crown Facet|
|crown step||Crown Step Facet|
|l.h.||Lower Half Facet|
|main||Pavilion Main Facet|
|pav corner step||Pavilion Corner Step Facet|
|pav facet||Pavilion Facet|
|pav step||Pavilion Step Facet|
|u.h.||Upper Half Facet|
*Reports for all diamonds graded later than 30th January 2012 should include only the terminology and abbreviations listed in this document. You may come across non-standardised information on diamonds graded prior to 30th January 2012 including the use of the modifiers listed in the table above.
“Sl” and “+” were typically applied to both Polish features and Symmetry deviations, while “fnt” and “hvy” were applied exclusively to Polish features. The modifier “+” referred to multiple facets of the same type with a given polish feature, or multiple facets of the same type with a given symmetry deviation (Ex. TP: l.h.+; MM+).