The details of a diamond’s cut are referred to as its finish. Finish is made up of two categories; Symmetry and Polish. Symmetry is the exactness of the shape and placement of a diamonds facets and polish is the overall condition of the facet surfaces.
Almost all diamonds on the market today have some minor symmetry problems; which are usually not visible to the unaided eye and have very little effect on a diamond’s appearance and beauty.
To evaluate symmetry, gem laboratories consider the evenness of a diamond’s outline and the size, shape, and placement of its facets. For grading purposes, two types of symmetry are considered; proportion symmetry and facet symmetry. Proportion symmetry is the alignment and balance of the diamond’s table, culet, girdle, and angles while facet symmetry is the shape, placement, and presence or absence of the facets themselves. Proportion symmetry and facet symmetry make up the diamond’s symmetry rating.
Before assigning a symmetry grade, GIA and other gem laboratories look for symmetry variations under 10x magnification. A diamond’s symmetry grade and the abbreviation of the symmetry characteristic are listed on all diamond grading reports.
The GIA symmetry grades are: Excellent (E), Very Good (VG), Good (G), Fair (F), and Poor (P)
The AGS symmetry grades are: Ideal (AGS 0), Excellent (AGS 1), Very Good (AGS 2), Good (AGS 3, 4) Fair (AGS 5, 6, 7), and Poor (AGS 8, 9, 10)
Common Variations in Proportion Symmetry
Crown angle variation (CV)
Culet off-center (C/oc)
Extra facets (EF)
Girdle thickness variation (GTV)
Misalignment of crown and pavilion facets (Aln)
Misshapen facets (Fac)
Missing facet (MF)
Non-pointing (Ptg)
Out-of-round girdle outline (OR)
Pavilion angle variation (PV)
Table off-center (T/oc)
Table/culet alignment (T/C)
Table and girdle not parallel (T/G)
Wavy girdle (WG)
Excellent and Very Good symmetry grades are rare. Diamonds with a symmetry grade of Good offer exceptional beauty and are the most frequently purchased diamonds today. Diamonds with a high symmetry grade are more important in diamonds that have very high clarity grades such as flawless or internally flawless than diamonds with a lower clarity grade. Symmetry is important for both round brilliant cut diamonds as well as fancy cut diamonds.
When budget allows, Since 1910 recommends purchasing a diamond for an engagement ring with a symmetry grade of Good or higher.
To learn more about diamonds, visit our diamond education section.
