What is the 'UV test' when judging if a diamond is genuine?

What is the 'UV test' when judging if a diamond is genuine?

John Cordova (Vice President of Human Resources, Robbins Bros.) gives expert video advice on: How do you tell if you have a treated diamond?; If I can scratch glass with my stone, does that mean that I have a diamond?; How can I tell a diamond from a fake using a newspaper? and more...

When judging whether a diamond is genuine, use the U.V. test. What you're looking at is, something that's based on the fact that a percentage of diamonds fluoresce under U.V. light. So if you take your diamond, the stone that you have, and you place it in a U.V. light unit, and it fluoresces, chances are, that is a diamond. The problem with that test is, a percentage of diamonds don't fluoresce at all. So no fluorescence doesn't necessarily mean that the stone you're looking at isn't a genuine diamond.