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Diamond Colour is one of the most important factors to consider, as it is noticeable to the naked eye. A diamond's colour is graded by GIA on an alphabetical scale from D to Z, with D being absolutely colourless and Z being light yellow. Beyond Z-colour, a diamond is considered to be a "fancy" colour.

A diamond's colour has a significant impact on its value. 

images of the colour scale of white  diamonds
colour scale of white diamonds
images of side view of diamonds showing check for diamond colour

Fluorescence is the visible light some diamonds emit when they are exposed to invisible

Ultra violet (UV) rays. Fluorescence refers to the strength, or intensity, of the diamond’s reaction to long-wave UV, which is an essential component of daylight. The light emitted lasts as long as the diamond is exposed to the ultraviolet source. Approximately 25% to 35% OF Certified Diamonds exhibit some degree of fluorescence. However, only 10% of those show strengths of fluorescence that may impact appearance (i.e., strengths noted on laboratory reports as medium, strong or very strong).

Fluorescence is not directly related to a diamond's colour. This separate characteristic refers to the diamond's ability to fluoresce under ultraviolet (UV) light. Our sun emits some UV light, but it is usually not great enough to detect fluorescence. When exposed to UV light, many diamonds will give off a distinctive glowing blue coloration. Although fluorescence may be

displayed in various colours, blue is the most common in diamonds. The fluorescence of a diamond is defined by its intensity as either None, Faint, Medium, Strong, or Very Strong. Although fluorescence is a characteristic that can be measured, it is rarely an issue when selecting a diamond and is usually not detectable to the eye.

The impact of fluorescence on price depends on its noticeability. Faint fluorescence has very little effect on a diamond of any colour, and therefore has no effect on value. For some higher colour stones (D to G), strong fluorescence may give the stone a milky white appearance, which greatly lowers the value. Fluorescence often adds value to stones with a hint of colour, such as I-colour and below, as it can give the diamond a whiter, brighter appearance.

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