Diamond Cut Introduction
What makes one diamond sparkle while another looks lifeless and dull? A good diamond is dazzling, romantic and priced according to quality. The most important factor is the grading and evaluation of a diamond’s cut. The purpose of this lesson is to provide a basic understanding of the evaluation of cut and proportioning and how it impacts a diamond’s beauty and value.
|Parts of a Diamond
Parts of a diamond are named by the various facets. It is important for any jewelry industry professional to learn the parts of the diamond to be able to properly communicate with consumers and dealers regarding diamond evaluation. Let's take a look at the facets and parts.
The numbers beside the facet indicate how many of each facet is in one modern, brilliant cut diamond. This number may vary with different cutting styles, but for our purposes the modern brilliant is the mainstay of our study. To read definitions of each term, view the diamond glossary. Below are some different cutting styles you may encounter.
Ideal Diamond Cut - (Part 2)
Diamond proportioning began in 1919 when a mathematician named Tolkowsky used numerical formulas to achieve the modern brilliant cut. He did this by cutting a diamond so that all light entering the stone followed a controlled path to exit the top of the diamond.
In 1919 the diamond cutting industry was not advanced enough to apply Tolkowky’s mathematical angles and dimensions. Instead it used variations of the cut, based on what the technology of the time could do. As technology advanced, so did the ability to better approximate the ideal Tolkowsky cut, which provides the best return of light in a diamond. It is possible for an experienced diamond grader to estimate, within a decade, when an older diamond was cut by observing where on the technology timeline its proportioning falls and how well is achieves Tolkowsky's ideal cut formula.
The image below shows the purpose of a diamond cut. The best cut casts a perfect shadow on a wall when a beam of light is shone on it. Very few will do that because, due to many factors, most diamonds deviate from the perfect cut. The perfect cut diamond is difficult to achieve, and many people differ as to what is a perfectly cut diamond. Since we are dealing here with a practical view of diamond cut evaluation, let's assume the image below is a perfectly cut diamond and see how it reacts to light.
A properly cut diamond is proportioned so that no matter where light enters the stone...from the top, sides or bottom… the light is directed out the top of the stone. This is difficult to achieve, but mathematically possible. The reason is that a diamond is cut to capture light entering it from a 360-degree sphere.
Controlled Path of Light
In a properly cut diamond, all light entering, no matter from what direction or angle, will always exit out the top of the stone. This is what makes a diamond sparkle.
The three images below are not drawings but rather are from a demonstration tool sold by the GIA. It is an excellent method of demonstrating how light reacts in a diamond.
| Deep Cut Diamond |
In this image the light is exiting the side of the diamond. This is because the stone is too deep and the light is not being controlled to go out the top. Some diamonds are cut to have maximum weight rather than maximum beauty. This is an example of that kind of diamond and the effect this cutting has on the beauty.
Cut too deep to retain weight, not beautiful
| Shallow Cut Diamond |
Looking from the top, it appears to be much larger than it really is. This is called a "fish-eye" or sometimes a "swindle cut," so called because you can take a diamond of.80 ct with this type of spread cut and make it appear as a 1.00ct diamond. Some people are fooled into thinking that they are getting a larger diamond for the money.
Cut too shallow to appear larger than it is, light is lost
|Ideal Cut Diamond |
In this image, you can see that the light is going in the top, traveling around the diamond interior and exiting out the top of the stone. No matter where the light enters this diamond, the light will go out the top. This is a brilliant and beautiful stone.
Ideal cut diamonds are always more beautiful!!!
Remember, these are actual light demonstrations and NOT drawings. The deep cut and shallow cut diamonds above could be VVS1 clarity and G colors, while the ideal cut diamond could be a SI2 clarity and I color. Which do you think would be the most beautiful? The right answer is the ideal cut diamond. Why? Because it is more brilliant. This is known as “Flash for the Cash” – the amount of brilliance in your diamond.
“Flash for the Cash” is crucial in diamond evaluation and diamond buying. Cut and proportioning can account for a 20 to 40 percent difference in price between diamonds that are otherwise equal. In other words:
Store A may offer you a SI1/H 1.00ct diamond for $6,500.00.
Story B may offer you a SI1/H 1.00ct diamond for $5.000.00.
You may think that Store B is giving you a significant discount directly from the wholesaler or the diamond mines, but what they don’t tell you is that you are getting a shallow or deep cut diamond and not an ideal cut. Remember, when you shop for diamonds there is more to diamond grading/pricing than just clarity and color. There is also the cut grade.