CaratThe GIA turns a light on fluorescence
From the fourth quarter the laboratory will add language to its reports separating fluorescence that changes a diamond's look from fluorescence that does not, addressing a stigma that has discounted a quarter to a third of all stones since the 1990s.
One of the most persistent discounts in diamonds is about to get a footnote. From the fourth quarter of 2026, the GIA will add clarifying language to its grading reports to distinguish when fluorescence changes a diamond's appearance from when it does not.
This is a rare case of a grading change that helps the buyer and the seller at once, by pricing a stone for what it looks like instead of what it might do. Read the new line when it lands, because a diamond that glows and shows nothing for it may be the best-value stone in the case.
| Figure | |
|---|---|
| Show Some Fluorescence | 25–35% |
| None | ~65–75% |
IA footnote on a discount
The trade has called it one of the biggest steps a laboratory has taken to address a trait that between 25% and 35% of diamonds carry to some degree.
Fluorescence, the soft glow some diamonds give under ultraviolet light, has been priced as a defect for decades even though it rarely is one.
In most stones it does nothing visible; in a small share it can lend a milky or oily cast to high-color goods, and the market long ago collapsed those two very different cases into a single penalty.
Rapaport has published fluorescence discount estimates since 1993, tracking a haircut that persisted through every swing of the market.
IIPriced as a defect
The fix is information, not chemistry. By stating on the report whether the fluorescence actually affects the look of the specific stone, the GIA lets a buyer separate the harmless from the compromised, and lets a seller defend a price rather than accept a reflex discount.
For a sizable, long-misunderstood slice of the market, transparency about the trait could carry real weight with the trade and the shopper alike.
IIIInformation, not chemistry
The commercial stakes sit with the middle of the counter. Faint and medium fluorescence in the near-colorless grades is exactly the material a value-minded consumer buys, and a clearer report gives the honest retailer a tool to reclaim margin that the blanket stigma has been quietly bleeding away.
01Method · the desk’s arithmetic+
Share of diamonds exhibiting fluorescence, per GIA. Midpoint shown.
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