Fluorescence can make a colorless diamond glow blue but the addition of the element boron gives a blue diamond its color.

Colored Diamonds

Colored diamonds are rare at a ratio of one colored diamond for every 10,000 colorless diamonds.  Colored diamonds occur in a variety of colors including yellow, brown, gray, orange, green, blue, white, black, purple, pink and red.  In order for a diamond to be colored, it must contain the addition of a trace element as is the case with the blue diamond, which contains boron.

What Is Fluorescence?

Fluorescence is the term given to diamonds that glow colors such as blue, yellow, orange, green or a combination of these colors.   Twenty-five to thirty-five percent of all diamonds have some strength of fluorescence.

When Does Fluorescence Occur?

Diamonds are composed of pure carbon arranged in lattice-like crystal structures.  Fluorescence occurs when one or more carbon atoms are missing.  These missing atoms are sometimes replaced by nitrogen atoms that are visible when exposed to ultraviolet rays.  The number of nitrogen atoms determines the color of the fluorescence.  For instance, one nitrogen atom will appear yellow, while three nitrogen atoms will give a diamond a blue glow.

The Largest Blue Diamond in the World

Once a 112-carat sapphire blue gemstone and believed to be part of Louis VIX French crown jewels, the Hope Diamond was cut into a 67-carat heart before it was stolen in 1672.  What is now known as the Hope diamond that is on display in the Smithsonian reappeared as a 45.5 carat diamond named for it's owner Thomas Hope.