Proportions
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Proportions
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Proportions Just how important is a diamonds cut quality?
Do you see the "fricken laser beams" coming out of this diamond? Well... if you want your ladies diamond to literally dance before her eyes you BEST PAY CLOSE ATTENTION TO THE FOLLOWING SECTIONS! How many web sites or jewelry stores have you visited, THAT DO teach about cut actually show you how well the stone you're considering purchasing is cut? There are sites here on the net that have this little picture of what an "Ideal Cut" is. There are also sites that define an Ideal Cut in different ways and don't even consider pavilion depth/angles and crown height/angles but only "total depth and table" when it comes to the proportions.
With all the Web sites selling diamonds and have huge lists of diamonds they have in stock, how many actually tell you what these dimensions are? At best, if the diamond is accompanied by a GIA lab report you'll at least get the table percentage, total depth percentage, girdle and culet size. Is this information specific enough to tell you about the proportions? How important is it for you to know what the pavilion and crown information is and how does it affect the brilliance? IT IS VERY IMPORTANT! This is probably the most important part of this site you're going to hit, so make sure you absorb what you're going to learn in this section, because the proportions can either make or break a stone and can affect the value by up to 40%. That's a lot of money. Take your time to go through this section here on proportions, because this one factor can affect the value in the diamond by up to 40%. How a Diamond Handles LightThere are 2 different types of light that can emanate from a diamond. One is called brilliance and the other fire. The brilliance is the return of white light to the human eye, the fire is the return of colored light to the human eye. These are not subjective terms, but can be scientifically defined and examined. The movement of both white and colored light within the diamond as it is moved before the observer is properly called scintillation. When a diamond has good brilliance and fire, it's scintillation will also usually be very good as well. Suppose the same amount of light should fall on a pile of black carbon powder as on a cut diamond. Both are formed from the same chemical, but clearly they will handle that light in quite different ways. Most of the light which falls on the powder is absorbed, which is why it appears black. But when light strikes a diamond, part of the ray is reflected from the surface. This is called EXTERNAL REFLECTION. Since the table facet is the largest facet on the diamond and is directly on top, the size of the table is going to directly affect EXTERNAL REFLECTION. This is the white light people observe as they look at a diamond. If the table facet is too big or too small you are going to get an unbalanced display of reflected light and dispersed light. An acceptable table size that falls at about 52-64% of the diameter of the diamond will give you a balanced display of both white and spectral light, so long as the pavilion is proportioned right. Read on to learn more.
Here's a live picture I caught digitally of a good example of external reflections of white light off of facet surfaces. The diamond on the left has white light reflecting from above off of a kite (bezel) and star facet. The diamond on the right, the kite and one of the upper girdle facets.
The other part of the ray enters the diamond and, as it does so, it bends due to the greater optical density of a diamond. This is called REFRACTION. The light is then reflected from the internal surfaces of the diamond - which is called INTERNAL REFLECTION.
The bottom portion of the diamond, called the pavilion, has direct bearing on the internal reflections and the light that is refracted through the diamond. If the pavilion angles don't fall between 40.5-41.5º and the pavilion depth does not fall between 42.2-43.8% of the diameter of the diamond the light will not have the internal reflection that is displayed in the above diagram. When pavilion angles fall less than 42º and the pavilion depth falls less than 42% of the diameter of the diamond, this is what results.
Now here's what happens to internal refracted light when the pavilion angles fall between 40.5-41.5º and the pavilion depth is 42-43.8% of the diameter.
The ray then emerges from the top of the diamond where, once again, it is bent or refracted and is separated into the colors of the spectrum. It is this DISPERSION that gives the diamond it's fire. The part of the diamond that is directly responsible for the amount of dispersion you're going to see, is the crown facets and the crown angles. Crown angles that fall within 33-35 degrees, a crown height between 14-16.2%, coupled with a 53-57.5% table will give a nice array of both white and spectral light, so long as the pavilion is cut right. Now this wasn't too hard to understand now was it?
These next few pictures are taken of super ideal cuts that are typical of the quality of diamond we feature here on "The Ultimate Diamond Information Site". These are the rarest and most beautiful cut qualities in the world and exhibit the most fire and dispersion that is possible to get in a diamond and a very good example to show you what is meant by dispersion.
Look at the colors coming off of that huh? Look at the pinks, blues, yellows, violets ... Is cut quality important? If you want your diamond to really glimmer YOU BETTER be insistent about cut quality. While I have these other graphics and instruments to demonstrate the importance of cut ... the above pictures say it all. The TOTAL BRILLIANCE of the diamond depends on the amount of internal and external reflections of light from the diamond to the eye. SummaryIn the above teaching I've given you some basics to work with. You now have an idea of what the "acceptable" standards are for a round brilliant cut diamond. A simple chart with the above tolerances would be...
Update 2001: It's been around a year now since I've been working with instrumentation that analyses the light return of diamonds. These numbers listed above are based off of research done by gemologists who had very limited resources to retrieve their conclusions from. From research I've done with the various instrumentation I use to analyze light return, myself and other people who are involved in these studies have found the same things I have. So... there are various sets of proportions from the above diagram that are great ... and also ones that are not so great. For example a diamond with 37 degree crown angles and a 45% pavilion depth would really stink. =O Read on to learn more... :)Now... you might be asking... there are a lot of numbers there. Is there such a thing as a "perfectly cut" diamond? To learn the truth about what a real ideal cut diamond is let's proceed to the next page. Click next. :)
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On the left is an example of diamond that tend to look bigger than what they
weigh, but see that solid beam of light falling out the bottom of the stone?
That's because of a shallow pavilion. All that light that's leaking out the
bottom is light that should be hitting someone in the eye... LIKE YOUR GIRL!
Part of the internal light is reflecting out of the opposite side, but you are
still not getting max brilliance. Understand?
Here
is a representation of a diamond that would have pavilion angles greater
than 42º and a pavilion depth that is greater than 45% of the diameter. Notice
how all internal refracted light reflects off one side of the pavilion only to
escape out the bottom of the other side. THIS TOO IS BOGUS!
BINGO!!!
Do you now understand the importance of pavilion depth??? I hope so because this
one factor can make or break a diamond. All refracted light is reflected
off those pavilion facets and BANG, that baby talks!!! 
