Fluorescence Grade Guide

Diamond fluorescence explained. Why D/E with Strong fluorescence trades at a discount, and why Medium fluorescence on I/J/K can actually be a bonus.

The fluorescence discount is real and sits mostly at the top of the color scale. A D color stone with Strong fluorescence can trade 10 to 20 percent below its non-fluorescent equivalent, because the market is worried about the hazy-in-sunlight risk (which shows up in only a small percentage of strongly fluorescent D stones). At I color and below, the discount disappears or even reverses, because fluorescence is working in the buyer's favor visually. None and Faint fluorescence are always safe and carry no discount.

The simple rule: at D to H color, stick to None, Faint or Medium fluorescence; avoid Strong and Very Strong unless you inspect the stone in natural daylight first. At I color and below, Medium is often a bonus and worth considering for the color-boosting effect in daylight. Very Strong is rare and best avoided without an in-person inspection.