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Welcome to Tradeshop Incorporated's Diamond Info Area.
Diamond grading standards fall into four distinct categories, the "Four C's":

Think of these as sliding scales
Grading A Diamond's Cut

Cut, one of the 4 C's of diamonds, used to commonly refer to the diamond shape. Today in the diamond industry, when talking about cut, we're referring to a diamonds' proportions, not shape. It is the most important factor in a diamond's brilliance, as well as maximizing it's apparent size in relation to it's weight, thus, it's impact on the value of a diamond can mean as much as 25-30% of it's cost. Since it's all about light optics, to produce the maximum effect, the cut is critical to the beauty of a diamond. A well cut diamond allows maximum light return from the top of the stone, while one cut too deep or too shallow allows light to pass out the pavillion, or bottom of the diamond, resulting in less sparkle.

Further down, I'll cover cut, in relation to the most popular shapes.

What's "ideal" for the Round Brilliant

Starting with the round brilliant diamond, which as of mid-2008, is the only shape to be given a rating based on it's proportions, as well as color, clarity, and carat weight, from all 3 major grading laboratories most recognized world wide. Rather than trying to explain the differences, here are links to the individual laboratories explaining their own particular methods of analogy. AGS(American Gem Society), EGL(European Gem Lab), and GIA(Gemological Institue of America), considered the "premier" grading laboratory in the industry.

Keep in mind, since each lab has slightly different scales for their rating of cut, there is a "range" that generally qualifies for what's "ideal" for the round brilliant diamond. So don't get too hung up on one set of numbers or you'll drive yourself crazy trying to find that one and only "perfect" diamond! However, a simple rule of thumb for the "ideal" round brilliant is one with a depth in the range of about 58.5%-62.5%, and a table from 53%-58%. Like I say, that varies somewhat from which lab grades the diamond, particularly on the higher side of those percentages, but one's in that range consistently have wonderful brilliance and liveliness.

What's "ideal" cut in Fancy Shapes

As for what's referred to as "fancy shape" diamonds, the most common being the heart, marquise, oval, pear, princess, radiant, trilliant, and emerald cuts, there are only industry guidelines that are generally accepted within the trade as having the optimal result in terms of cut. There is no established "ideal" cut by any of the major labs on any of these shapes, other than for the princess and emerald cuts from AGS. So when you see or hear someone expressing a certain diamond in these shapes as being "ideal", it is only their opinion, which just like with the round brilliant, you'll get varied "opinions".

So, with that in mind, for the heart, marquise, oval, and pear shapes, I generally look for ones with depth and table both in the range of about 58-64%. For the princess, radiant, and emerald cuts, I look for both depth and table somewhere in the 60% range or into the low-mid 70's. Depth for a trillion should fall in the low-mid 30's to mid 40's range, with the table percent in the low 50's to mid 60's range.

Ideal Shape?

It really drives me crazy when I see or hear a retailer quoting a particular fancy shape as "ideal", or saying the "ideal" shape is this or that when talking about length-width ratio, also referred to as it's "aspect ratio", because that really comes down to personal preference, so let's look at these.

Emerald cut: This cutting style is what is called "step faceted" as opposed to "brillianteered" faceting, used for the round and other brilliant cut shapes. I like to describe a emerald cut as looking into a clear pool of water. At least if the diamond is at the level of clarity that no inclusions can be seen with the eye : ) That typically starts at the VS2 level. With this cut, you'll see flashes of light as it's tilted back and forth, kind of like the flashes you see bouncing off the ripples when throwing a rock into a still pool on a sunny day, but not the kind of "brilliance" that you see with the other cuts. The "classic" rectangular shape for the emerald cut would have about a 1.30:1 up to 1.50:1 l-w ratio. Depending on personal preference, you can find these with a much longer/more slender shape, all the way down to square in shape, often referred to as a Asscher cut, although not a true Asscher.

Heart shape brilliant: What you most commonly see is a fairly symmetrical shape within the range of l-w at 1:1 to 1.1:1, however you will find some either more elongated up and down, or the opposite, being wide and short. Depth and table preferrably in the range of about 58-64%.

Marquise brilliant: This is more or less the shape of a football. What is typically most desireable is a l-w in the range of 1.75:1 up to about 2.10:1. On the low end it starts looking much fatter than longer, and getting past the upper end it becomes much more slender. Depth and table preferrably in the range of about 58-64%. This cut will tend to have what's called a "bow-tie" effect in the middle of the stone because of it's cutting style. This cannot be totally eliminated, and is partially what makes this cut unique. However, a poorly cut stone will exhibit a overly dark bow-tie.

Oval brilliant: The overall shape is self explanatory. The "classic" look of this cut will have a l-w ratio from about 1.30:1 up to about 1.45:1. On the low end it starts looking much fatter than longer, and getting past the upper end it becomes much more slender. Depth and table preferrably in the range of about 58-64%. As with the marquise,this cut will tend to have what's called a "bow-tie" effect in the middle of the stone because of it's cutting style. This cannot be totally eliminated, and is partially what makes this cut unique. However, a poorly cut stone will exhibit a overly dark bow-tie.

Pear brilliant: This cut has the shape of a tear drop. As with the oval, the "classic" look of this cut will have a l-w ratio from about 1.30:1 up to about 1.45:1. On the low end it starts looking much fatter than longer, and getting past the upper end it becomes much more slender. Depth and table preferrably in the range of about 58-64%. Also, as with theoval and marquise,this cut will tend to have what's called a "bow-tie" effect in the middle of the stone because of it's cutting style. This cannot be totally eliminated, and is partially what makes this cut unique. However, a poorly cut stone will exhibit a overly dark bow-tie.

Princess brilliant: Similar in appearance to the Radiant cut but with pointed corners. Most consider this to be a perfect or near perfect square, when actually you can find some that are somewhat rectangular to quite rectangular. Look for both depth and table somewhere in the 60% range into the low-mid 70's. It doesn't matter which has the higher or lower percentage, just as long as both are in that range.

Radiant brilliant: Similar in appearance to the Princess cut but with clipped corners. Typically this cut has a subtle rectangular shape to it with l-w ratio running in about the 1.10:1 up to around 1.20:1. This cut can also be found square shaped as well as more rectangular shaped. Also as with the Princess cut, look for both depth and table somewhere in the 60% range into the low-mid 70's. It doesn't matter which has the higher or lower percentage, just as long as both are in that range.

Trilliant brilliant: Traiangular in shape, typically cut with slightly curved sides, although some are cut with straight sides. Measureing from base to opposite point, these are typically in the range of 1:1 to 1.10:1 for their aspect ratio between the longest and shortest mesurements of the three sides. No other shape has a more broad range for depth and table! In this cut, I personally prefer one with depth in about the 35-45% range and table in the mid 50's up to mid-upper 60% range. In this range it has more of a sparkle like the other brilliant cut shapes. A lower depth will also have brilliance to it, but it's more a crinkley look, like crumpled aluminum foil.

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