Lesson 42 · Diamonds & Engagement Rings · 38 seconds
Why some diamonds glow under UV
Under ultraviolet light, some diamonds give off visible light, called fluorescence. Many show none, while others glow faintly or strongly, most often blue, and fluorescence stops when the UV is removed; a lingering afterglow is a different effect. It is not a test: natural and lab-grown diamonds can both glow, and some imitations do too.
What this lesson shows
A glow under UV is not a test.
An illustrated dark-room scene shows five loose diamonds under an ultraviolet lamp: two glow soft blue, one glows faintly and two show no glow, and the moment the UV is removed, the glow is gone. A simplified diagram shows ultraviolet light going in and visible light coming out.
Three quick takeaways
What to actually do when you shop
- Under ultraviolet light, some diamonds give off visible light. Many show none; others glow faintly or strongly, most often blue. Fluorescence stops when the UV is removed; a lingering afterglow is a different effect.
- The glow is not a test. Natural and lab-grown diamonds can both glow, and some imitations do too.
- Fluorescence strength is listed on many grading reports, but the glow alone does not tell you what a stone is.
Read the transcript
Why does this diamond glow blue? Under ultraviolet light, some diamonds give off visible light. That's fluorescence. Many show none, while others glow faintly or strongly, most often blue. Fluorescence stops when the UV is removed; a lingering afterglow is a different effect. And it isn't a test: natural and lab-grown diamonds can both glow, and some imitations do too. Fluorescence strength is listed on many grading reports. Explore more in the Aydins Jewelry Learning Center.
Sources
- GIA, diamond fluorescence: 4cs.gia.edu/en-us/diamond-fluorescence/
- GIA, fact checking diamond fluorescence: 11 myths dispelled: 4cs.gia.edu/en-us/blog/fact-checking-diamond-fluorescence-myths-dispelled/
- GIA Gems & Gemology, Summer 2013: fluorescence produced by optical defects in diamond: www.gia.edu/gems-gemology/summer-2013-luo-fluorescence-optical-defects
Related lessons
What a diamond tester beep tells you · why a beep is a screening result, not an identification.
Three checks before trusting a diamond report · how to read and match a report.
Lab-grown diamond vs cubic zirconia · what makes a diamond a diamond.
Next step
Explore lab-grown diamond jewelry.
Compare the specifications listed on each piece.