A GIA Excellent cut grade doesn't guarantee a beautiful diamond. Roughly 30–40% of stones graded Excellent have proportion combinations, symmetry quirks, or facet manipulation that kill light performance. The grade is a range, not a guarantee. I reject Excellent-cut diamonds every week.
Why Does GIA Excellent Allow So Much Variation?
GIA's Excellent cut grade covers a wide range of proportions. A 34.5° crown angle with a 40.8° pavilion angle will look different from a 35° crown with a 40.6° pavilion — but both can grade Excellent. The system evaluates proportion combinations, not single numbers, and the acceptable window is broader than most buyers realize.
According to GIA's own research on their cut grading methodology, approximately 33% of round brilliants fall within the Excellent range. That's not a narrow elite tier. That's a third of the market.
The result: two diamonds sitting side by side, both triple Excellent on paper, and one is a firecracker while the other looks like a piece of glass. The certificate doesn't tell you which is which.
What Are Painting and Digging — and Why Should You Care?
This is where it gets ugly. Painting and digging are facet manipulation techniques cutters use to retain weight from the rough while staying inside the Excellent grade boundaries. Most buyers have never heard of either one.
Painting involves cutting the lower girdle facets at a shallower angle so they align closely with the pavilion main facets. On paper, the proportions still check out. In reality, the lower girdle facets stop acting as independent light reflectors. You lose contrast patterning — the arrows in an ideal-scope image get bloated and washed out. The diamond looks flat.
Digging is the opposite manipulation on the upper half facets, steepening them to the point where the star facets virtually disappear into the bezel facets. Again, perfectly gradeable. Again, visually destructive.
Neither painting nor digging appears on a GIA report. You need magnification, ASET imaging, or Idealscope analysis to catch it. Or you need a dealer who's looked at thousands of stones and can spot the light leakage on sight. I've seen painted stones listed at premium prices by vendors who either don't know or don't care.
How Does Obstruction Kill an Otherwise Good Diamond?
Obstruction is the least discussed problem. When light enters a diamond and hits the pavilion facets, some of it reflects back toward the observer's head and body rather than toward the eye. Your own head becomes a dark shadow blocking the returned light. This is called obstruction, and it's a function of crown angle and table size working together.
A large table with a shallow crown is the classic obstruction setup. The diamond looks dark in the center under certain lighting — not because of inclusions, but because of physics. You'll see this in a lot of the "spread" stones that dealers push for their larger face-up appearance relative to carat weight. The trade-off is light performance, and it's a bad trade.
Why Don't More Dealers Talk About This?
Because triple Excellent sells. The certificate says Excellent three times, and most buyers stop reading. It's an easy transaction for everyone in the pipeline — the cutter retains more weight, the wholesaler has a marketable certificate, and the retail jeweler doesn't need a loupe or a conversation about facet geometry.
I sit at Rapaport-priced tables in the Diamond District every day. The spread between a genuine top-performing Excellent and a mediocre painted Excellent can be 15–20% in cost — but the visual difference is enormous. Informed buyers exploit that gap. Uninformed buyers overpay for dead stones.
What I look for: crown angles between 34° and 35°, pavilion angles between 40.6° and 40.8°, table sizes under 58%, no painting, no digging, and strong contrast patterning under structured lighting. That narrows the Excellent pool dramatically. Maybe the top 10–15% of stones graded Excellent actually perform like it.
The certificate is a starting point. If it's the only thing you're evaluating, you're buying blind.
Q: Can a GIA Excellent cut diamond look bad?
A: Absolutely. The Excellent range is wide enough that stones with mediocre light performance qualify. Proportion combinations at the edge of the range, combined with painting or digging, can produce a diamond that looks dull despite perfect grades on paper.
Q: What is painting and digging in diamonds?
A: Painting and digging are facet manipulation techniques cutters use to maximize carat weight retention. Painting aligns lower girdle facets with pavilion mains, killing contrast. Digging steepens upper half facets into the bezels. Neither shows up on a GIA report — you need imaging or experienced eyes.
Q: What diamond proportions give the best light performance?
A: For round brilliants, I look for crown angles of 34°–35°, pavilion angles of 40.6°–40.8°, and table sizes under 58%. That combination, without painting or digging, consistently produces the strongest fire and brilliance. It's a much narrower window than what GIA calls Excellent.
Q: Is triple Excellent the best diamond cut?
A: Triple Excellent means the stone scored Excellent for cut, polish, and symmetry — but it's a range, not a pinnacle. I've handled triple Excellent stones that were visually outperformed by stones with slightly lower grades but better-optimized proportions. The label doesn't replace actual visual evaluation.
Lawrence Paul
I've been recutting and repolishing diamonds since 2009 — it's one of the areas where the right call can add serious value. If you have a stone you're unsure about, send the cert and I'll tell you whether recutting makes sense. Reach me at info@spectrafinejewelry.com.