The cut of a diamond is the only property which is totally dependent on man. Although often overlooked, cut is actually one of the most important aspects to consider when choosing your diamond. A diamond cutter analyzes the rough diamond, and has to determine how to extract the most beauty and most profit out of the rough stone.

Cut refers to not only the shape of the diamonds, but its proportions and finish, factors which determine the sparkle of the diamond.

It is possible to take the same stone, and depending on which method the cutter decides to use, to either cut it into the most beautiful stone it can be despite heavy weight loss and perhaps lower monetary value. Or he can cut a stone to its maximum weight and monetary value, but lose some “brilliance” and “sparkle”!

You see, even if you have two equal polished diamonds, both the same carat size, both the same color, both the same clarity, they may look completely different. How? There are many different shapes, and facets in a diamond. The weight can be distributed in different parts of the stone.

The goal in terms of extracting the greatest beauty from a diamond, is to have light enter a diamond, disperse the light as it bounces inside the diamond, thereby producing the different colors and sparkly effect, and finally returning as much light to the eye as possible.

According to conventional wisdom, the proportions shown at the top of this page are the best for maximum light return. The 2-dimensional illustration to the right shows the theoretical path a ray of light will take through an ideal-cut Diamond. As you can see, the rays of light entering the Diamond, reflect back to the eye.

It is possible for a diamond cutter to extract more weight out of the diamond by increasing the diameter of the stone. This will make the stone too shallow, and light may escape from the side of the stone, as shown at right or leak out of the bottom of the stone, as shown at left.Another side-effect of this cut, is that it makes the stone appear larger. Don’t be fooled by this. The fact that it appears larger than it is does not make it a better stone. If you compare a shallow stone to a well-cut stone, you will see the difference in how the well-cut stone “lights up”.

By the same token, it is common to see the opposite problem. A stone which is cut too deep will “leak out light” in much the same way as the shallow stone. See two illustrations at right.

This is not to say that a shallow or deep stone is a sign of a poor, or “low-quality” diamond cutter. Sometimes the shape of the rough diamond makes it impractical to cut a stone closer to “ideal” proportions without losing significant weight. But it is important to note the “light leakage” which will result from this cut.

Recently, GIA has published the first report of their 8-year study of the cut of Diamonds, using a 3D model rather than the 2D model in use since the early part of this century. So far, nothing practical has come out of this research, other than making the point that there are definciencies in the 2-Dimensional model, and that there are a great many different angles and proportions which can be just as beautiful as what is accepted as Ideal-Cut today. This point is well known to anyone who has graded many Diamonds.

How much does “cut” affect cost?

The effect of all the different properties of Diamond on Cost is discussed in more detail in the Cost section. For cut, it can vary depending on the quality of the Diamond.