Diamond Polish
The final touch that determines how smoothly light passes through the surface.
After a diamond is cut and shaped, its facets are polished on a high-speed wheel coated with diamond dust. Polish refers to the quality of this surface finish — how smooth and defect-free each facet is. Microscopic polish lines, burn marks, or rough spots left from the cutting process can interfere with the passage of light and slightly reduce the diamond's brilliance.
Polish is graded under 10x magnification by trained gemologists. Like symmetry, it is one of the three factors (along with proportions and symmetry) that contribute to the overall cut grade for round brilliant diamonds.
Common Polish Defects
When grading polish, gemologists look for surface characteristics left by the cutting and polishing process:
- Polish lines — Fine parallel lines left by the polishing wheel. The most common polish feature.
- Burn marks — Whitish haze caused by excessive heat during polishing, usually from too much friction or pressure.
- Scratches — Fine lines on the surface from contact with other diamonds during storage or handling.
- Abrasion — Tiny nicks along facet junctions, giving edges a fuzzy or white appearance.
- Pits — Tiny holes on the facet surface, often caused by inclusions that were pulled out during polishing.
- Lizard skin — A bumpy, textured surface caused by irregular crystal structure in that region of the diamond.
- Rough girdle — A grainy or pitted girdle surface that has not been polished or faceted.
Polish Grades
| Grade | Abbreviation | What It Means | Our Advice |
|---|
| Excellent | EX | No polish defects visible under 10x magnification. The surface is flawlessly smooth, allowing maximum light transmission. | The premium choice. Required for "triple excellent" diamonds. |
| Very Good | VG | Polish features are very difficult to see under 10x magnification. May include an extremely faint polish line that has no effect on appearance. | Virtually identical to Excellent in real-world viewing. Outstanding value. |
| Good | G | Polish features are difficult to see under 10x magnification. May include minor polish lines or a very small scratch, but not visible to the naked eye. | A good choice for budget-minded buyers. No visible impact on beauty. |
| Fair | F | Polish features are noticeable under 10x magnification and may be visible to the unaided eye. Multiple polish lines, scratches, or burn marks may be present. | Some light performance is lost. Upgrade if your budget allows. |
| Poor | P | Polish features are obvious and easily visible to the unaided eye. The surface appears rough or hazy, significantly reducing brilliance. | Not recommended. Significant impact on the diamond's appearance. |
How Polish Affects Value
Polish grade has a direct impact on price, though less so than cut grade, color, or clarity. The difference between Excellent and Very Good polish is typically 2–5% in price, while the gap between Excellent and Poor can exceed 15–20%.
In practice, the difference between Excellent and Very Good polish is virtually invisible to the naked eye. Both grades allow light to pass through the diamond's surface without meaningful interference. The difference only becomes apparent under magnification.
Our Recommendation
For the best balance of quality and value, choose Very Good or Excellent polish. The visual difference between these two grades is negligible, so don't overpay for Excellent if a Very Good polished diamond is otherwise identical. However, avoid Fair and Poor polish — the surface defects in these grades can dull the diamond's brilliance and are sometimes visible without magnification.
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