STR Fluorescence

What STR Fluorescence Means for Buyers

Fluorescence is how the diamond reacts to UV light. Most commonly a blue glow, but occasionally yellow or other colors. The trade has historically discounted strongly fluorescent stones, especially at the colorless end of the color scale. But for warmer-colored stones (I to M), medium fluorescence can actually make them look whiter in daylight.

Right now we're tracking 693,300 active STR fluorescence listings across our retailer network. The typical natural STR diamond trades around €2,173/ct while the lab-grown equivalent sits at €588/ct. Roughly a 73% gap that reflects the broader natural-vs-lab pricing gap, not a quality difference at this grade.

At 2.6% above the neighboring VST grade, the premium for STR is subtle. Barely enough to move the needle on total budget. Unless you specifically want the paper grade, VST is interchangeable for most buyers and leaves money on the table for cut or carat weight.

STR shows up most often in ROUND. About 399,133 listings at this moment. Followed by OVAL. Most of the supply clusters around the 0.5-0.99ct carat range, where demand is strongest and retailers keep the deepest inventory. If you're shopping an unusual shape or carat, expect thinner selection.

The simplest rule: at D to H, avoid Strong or Very Strong fluorescence. It can occasionally give the stone a slightly milky or hazy look in sunlight. At I and below, medium fluorescence is often a bonus that makes the diamond face up whiter. None and Faint are always safe.