Diamond Expertise

Diamond Fluorescence

Fluorescence is the glow you see when a diamond emits visible light. Only some diamonds fluoresce when they are exposed to UV ray sources such as the sun. Find out why, whether this is good or bad, and more in our guide.

What is diamond fluorescence?

Fluorescence is the soft, coloured light a diamond can emit when exposed to ultraviolet light sources, like the sun. Diamonds with no fluorescence or very minimal fluorescence are considered the most desirable, and noticeable fluorescence is considered a diamond defect. Diamonds with strong fluorescence usually emit a blue light and appear hazy when exposed to ultraviolet light.

Diamond fluorescence scale

Diamond fluorescence is graded with descriptive terms that indicate the severity of the fluorescence. The GIA rates diamond fluorescence as either None, Faint, Medium, Strong or Very Strong. During the grading process, the diamond will be compared to master diamonds of different fluorescence grades, until a match is found.

None - The diamond has no fluorescence

Faint (Faint Blue) - The diamond has minimal fluorescence

Medium (Medium Blue) - The diamond has slightly noticeable fluorescence, and may appear hazy sunlight

Strong (Medium Blue) - The diamond has noticeable fluorescence, and will appear hazy in sunlight

Very Strong (Very Strong Blue) - The diamond has severely noticeable fluorescence, and will appear very hazy in sunlight

Image via gia.edu

Try to avoid diamonds with fluorescence - and favour a high cut and colour grade, for a diamond that will appear bright, icy and super sparkly.

Adele | Gemmologist & Design Expert

Do all diamonds have fluorescence?

No, only around 30% of diamonds show fluorescence, so it is absolutely possible to find a diamond without fluorescence for your ring or piece of jewellery. Most gemmologists will agree, you should only consider diamonds with no fluorescence, or at the most, very minimal fluorescence.

Is diamond fluorescence good or bad?

Diamond fluorescence can be considered good or bad - depending on the diamond and its colour grade. In diamonds with a high quality colour grade, fluorescence is considered undesirable. Under ultraviolet light, like sunlight, the diamond may emit a medium blue or strong blue light, and cause the diamond to look hazy. In poorer colour grades, however, the blue light emitted can counterbalance the yellowness of the diamond. In diamonds colour graded I to M, a degree of fluorescence can be favourable, but the stone may look hazy in sunlight. At Queensmith, we recommend diamonds colour graded between D to F with None or Faint fluorescence, for a bright, icy, crisp and clear looking diamond.

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