Overview

When a rough diamond is cut into a polished gem, two qualities of the cutter's workmanship are graded independently: how smooth the facet surfaces are (polish), and how precisely the facets are aligned with each other (symmetry). Together, these two grades constitute the diamond's finish — a measure of craftsmanship that sits alongside the cut grade but evaluates different aspects of the stone.

Polish assesses the condition of each facet surface after the cutting wheel has done its work. A well-polished facet is perfectly smooth — light enters and exits without surface scattering. Poor polish leaves microscopic defects (scratches, burn marks, rough patches) that diffuse light at the surface, reducing the sharpness of reflections and the crispness of brilliance.

Symmetry evaluates how accurately the facets relate to each other in position, shape, and alignment. A symmetrical diamond has a centred table, evenly spaced facets, a consistent girdle, and a properly positioned culet. Symmetry deviations cause light to bounce at unintended angles inside the stone, reducing the precision of the light return pattern.

Both are graded on the same five-point scale: Excellent, Very Good, Good, Fair, Poor.

Key Concepts

Finish is separate from cut. The GIA cut grade for round brilliants incorporates proportions, brightness, fire, and scintillation. Polish and symmetry contribute to the cut grade but are also reported as distinct line items. A diamond can technically receive an Excellent cut grade with Very Good finish grades — the proportions and light performance carry the overall assessment. See Finish Overview.

Polish defects are surface phenomena. Scratches, burn marks, rough girdle texture, and "lizard skin" (a pattern of micro-pitting) are all polish characteristics noted on grading reports. Most are invisible to the naked eye at Excellent and Very Good grades. At Good and below, surface haze or visible scratches may reduce the diamond's ability to transmit light cleanly. See Polish and Polish Characteristics.

Symmetry deviations are structural. An off-centre table, misaligned crown and pavilion facets, a wavy girdle, or unevenly sized star facets are symmetry issues. These affect how light is directed inside the diamond — subtle misalignment means light does not return to the viewer's eye as efficiently as the proportions alone would predict. See Symmetry and Symmetry Variations.

EX/EX is the practical benchmark. Among well-informed buyers, "triple Excellent" (Excellent cut, Excellent polish, Excellent symmetry) has become a common search criterion for round brilliants. This is a reasonable standard, though not an absolute requirement — many Very Good finish diamonds perform beautifully, and the visual difference between Excellent and Very Good finish is often imperceptible without magnification.

Practical Tips

Target Excellent or Very Good in both polish and symmetry. This covers the vast majority of well-cut diamonds and ensures no finish-related light performance issues.
Do not overpay for "triple Excellent" as a rigid requirement. If a diamond has Excellent cut and Very Good polish, the visual difference from an EX/EX/EX stone is negligible. Use "triple Excellent" as a convenient filter, not a dogma.
Check the report for specific characteristics. If polish is graded below Excellent, the report will note which defects were observed. Most are benign at Very Good. At Good and below, ask for images showing the facet surfaces.
Symmetry matters more for Hearts & Arrows. If you specifically want a Hearts & Arrows diamond, Excellent symmetry is essential — the H&A pattern requires precise facet alignment that Very Good symmetry may not deliver.

What the Child Articles Cover

Finish Overview — How polish and symmetry combine into the finish assessment, how finish relates to the cut grade, and the EX/VG practical threshold.
Polish — What polish measures, how it is graded, and when polish grade affects visual performance.
Symmetry — What symmetry measures, facet alignment criteria, and how symmetry deviations affect light return.
Polish Characteristics — Burn marks, scratches, rough girdle, lizard skin: the specific surface defects listed on grading reports and their significance.
Symmetry Variations — Off-centre table, wavy girdle, misaligned facets: the specific alignment issues and their impact on light performance.

Dokončení: leštění a symetrie

Přehled dokončení

Leštění

Symetrie

Běžné charakteristiky leštění

Běžné odchylky symetrie