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How Does Sunlight Affect Diamond Fluorescence?

Diamond color is not related to fluorescence; it is a separate element referring to the diamond’s ability to fluoresce under ultraviolet (UV) light. Although the sun emits some UV rays in sunlight, it is generally not enough to detect most fluorescence. However, when exposed directly to UV light, many diamonds will glow with a blue coloration. Blue is the most commonly displayed diamond fluorescence, but other hues are possible. Diamond fluorescence grades include None, Faint, Medium, Strong, or Very Strong.

diamond fluorescence

Fluorescence’s Impact

Although fluorescence is a characteristic that can be measured, it is rarely an issue when selecting a diamond. This is because diamond fluorescence is rarely detectable to the eye. The impact of fluorescence on the value of a diamond depends on its noticeability. Since diamonds graded none or faint fluorescence have little effect on color, the value of these diamonds is not affected. However, some higher grade stones such as those rated D to G may contain a milky white appearance under UV light. This can greatly reduce the stone’s value. On the other hand, fluorescence often adds value to stones with a hint of color, such as I-color and below, as diamond fluorescence often gives the diamond a brighter appearance.

Diamond Fluorescence In Direct Sunlight

Although the sun’s UV rays don’t affect most diamonds, diamonds with very strong fluorescence glow blue under direct sunlight. While the amount of fire and brilliance is not changed, the diamond’s color appears blue. However, even very strong diamond fluorescence will still be faint in most sunlight. Ambient sunlight, such as the light that passes through windows into buildings, will not alter the diamond color. Therefore, while a diamond’s fluorescence may lower the value of a stone, it will still appear gorgeous with great sparkle in nearly every situation. For this reason, many shoppers on a budget will opt for a diamond with strong fluorescence when designing a custom engagement ring.

Learn more about diamond fluorescence in the Adiamor Diamond Color Education guide.

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Why Aren’t Fancy Shape Diamonds Given Cut Grades?

Of all the 4C’s, everyone can agree that it is Cut that has the most impact on a diamond’s sparkle, fire and brilliance- so why aren’t fancy shaped diamonds like the marquise, the cushion or the radiant shape graded on cut? The fact is that GIA only grades round brilliant diamonds and AGS grades both round and princess cuts; both of these well-known cut grades were only invented very recently- as in the 2000’s!

So why aren’t fancy shapes given a cut grade like rounds? Shouldn’t it be relatively easy to put together a comprehensive system for grading an oval as you would the round brilliant or a princess cut diamond- how hard could it be, right? Well the short answer is: Very.

Fancy diamond shapes are based off the two main faceting styles- brilliant and step cut faceting. This means there are nearly endless ways to modify the shapes to maximize light return, fire and scintillation by lengthening, shortening, adding or subtracting facets within the pavilion and crown of the gem. The diagrams below show just a few of the faceting variations the diamond cutter may employ to coax certain aspects out of the diamond rough when creating a cushion cut diamond shape:

Cushion Cut Diamond Faceting Styles
Cushion Cut Diamond Faceting Styles

Some of these faceting styles are meant to create the popular “crushed ice” look in which the diamond scintillates from all angles; the addition of the shorter facets in the pavilion actually causes light to reflect and refract back at the viewer at an accelerated rate. Other styles with more elongated facets are meant to emphasize the traditional Old Mine cut glimmer and higher rate of fire that is best shown off in candlelight.

Traditional Cushion Cut and "Crushed Ice" Cushion Cut Diamonds
Traditional Cushion Cut and “Crushed Ice” Cushion Cut Diamonds

All of them are gorgeous in their own way, but which has the better cut? It is true that beauty is in the eye of the beholder; one may prefer the fire and glimmer of the longer faceting style over the crushed ice and vice-versa, however we can agree that there are certain ideals to each shape to which the diamond cutter should strive.

Fire, brilliance, life- these attributes are all created according to set mathematical formula which determines the exact length and angles of the facets adjoining in perfect symmetry to ensure that light travels within the gem properly. This is the core of the issue- how to evaluate each diamond’s exact measurements, depth and crown angles to ensure that a diamond is ‘ideally cut’.

Adiamor has created (in conjuction with our diamond cutting partners and through decades of hands-on diamond experience) an easy to understand chart which details the Ideal through Good cut grades for each fancy diamond shape by determining a diamond’s depth and table percentages. Depth and table percentages are calculated by dividing the length of a diamond’s table or its total depth by its diameter; for example if a diamond’s total depth is 5.6mm and the diameter is 10.0mm, then its depth percentage is 56%. These mathematic formulas help us to be able to determine if a diamond will sparkle in an attractive manner, as they are loosely based upon the ideal brilliant cut faceting formula used for rounds which are graded. Combined with a diamond plot depicting the faceting style of the pavilion of the diamond, we are able to get a fairly good idea of how well a diamond has been cut.

Affinity Diamond Depth and Table Measurements
Affinity Diamond Depth and Table Measurements

As to why these fancy shapes aren’t officially graded by GIA and AGSL (among others) is simply that there are too many variations on each shape to keep up! Each year, there are new twists to a classic shape, evoking even more brilliance and beauty. However, expect this state to change in the future, as more and more people within the industry begin to agree upon particular parameters for table and depth percentages, length to width ratios and more, assigning a cut grade to these gems will become the norm.

For now, however, when shopping for fancy shape diamonds, just keep in mind that beauty is indeed in the eye of the beholder! The general appearance of the diamond should attract the eye and it should have plenty of brilliance and fire; try to find diamonds that have at least Very Good Polish and Symmetry as this means that both the facets align properly and are crisply polished, with defined junctures that pass light from one area to another. Work with your jeweler or gemologist to establish which table and depth percentages will ensure that your diamond has been cut to proper proportions and keep an eye on the length to width ratios to keep the diamond’s shape within normal parameters. Above all, love the gem you buy!

Loose Adiamor Diamonds
Loose Adiamor Diamonds