Bottom Line Recommendations
- When choosing your diamond, pay close attention to the crown angles and the pavilion angles. When the crown angles are shallow, the pavilion angle needs to be steep and vice versa. The pavilion angles need to be between 40.6 and 41 degrees. Anything beyond this will be too steep and light will get lost in the pavilion. Take a look at this round diamond with an ideal cut here.
- You may want a diamond with either more brilliance or more fire. If it is more brilliance, it is recommended to go for a crown angle that is nearer to 34 degrees. For more fire, go for a crown angle that is nearer to 35 degrees.
- The 34-degree crown angle will have more brilliance but it also needs to be compensated with a steep pavilion angle of 41 degrees.
- Note that the degree of the crown angle will have an effect on how the diamond appears face up. When it is shallow, the diamond will appear larger as more of the weight will be distributed towards the sides of the diamond. You can use this to pick a diamond that is lower in carat weight and get a great deal.
- Ensure that you view 360-degree videos of the diamond. This is the best way to evaluate its appearance. We recommend buying from James Allen or the Blue Nile.
Many factors can affect how a diamond’s physical appeal. Two of the most significant however are the diamond crown angle and the pavilion angle. The cutter can tweak the size of the crown if the stone has more depth on the pavilion, for example, to give the stone a more ideal look.
Let’s take a look at each of these in more detail, shall we?
The crown is the top part of the diamond. The crown and the table facet allow light to get into the stone. These facets will determine how bright the diamond is. Second, the crown also has the function of dispersing light into its different colors allowing the stone to show its fire.
The third function of the crown is bending light. The light that comes off through the crown is shifted compared to the light that comes off through the table. More virtual facets are visible as a result of the more facets on the crown. This increases the sparkle as well as the brilliance of the stone.
The diamond crown angle is the degree of separation between a diamonds girdle and the table. The position of the facets at the bezel is determined by this angle.
The lower half the diamond is called the pavilion and has facets that are designed to reflect and refract the light that gets through the table. The pavilion angle is the degree of separation between the girdle of a diamond and the table plane.
The ability of the diamond to revert light and act as a mirror is determined by its refractive index. This is the angle through which the light rays will bend once they enter the diamond through the crown.
The refractive index is important in a diamond as light can only be refracted when it hits the facet at an angle greater than its critical angle. This simply means that if a stone has a higher refractive index, it can be cut much steeper before light will begin to leak through the pavilion.
Consider a diamond with a lot of depth at the pavilion. When the light enters the diamond through the table, since the stone is not steep, the light will not leak out of the diamond after hitting the first pavilion facet. This is simply because the light is not bent enough to leak.
On the other hand, when the pavilion is too shallow, light entering the diamond through the table will be bent at a much more acute angle and will escape through the opposite facet instead of being reflected up.
In an ideal cut diamond, the light entering through the crown will be bent at the correct angle to be refracted back to the observer and much of it will not escape through the pavilion.
The Ideal Crown Angles
Keep in mind that the angle of the crown could compensate for how light bends once it hits the first facet on the pavilion. Generally speaking, when the angle of the pavilion is steep, the angle of the crown needs to be shallow.
That said, you would be forgiven for noting that there isn’t any perfect angle for the crown that would maximize light return with a given pavilion angle.
It was Marcel Tolkowsky, known as the father of the modern round cut diamond, with an engineering background and whose experience in diamond cutting ran in the family, who found that when a 40.75-degree pavilion angle was paired with a 34.5 crown angle, this resulted in maximum light reflection.
That said, it follows that if a diamond has a steep pavilion angle of 40.6 degrees, then it needs to compensate with a 35-degree crown angle.
On the other hand, when the stone has a 41-degree crown angle and is not bending light enough, it needs to compensate with a 34-degree crown angle.
After understanding the 34-35-degree range for crown angles, you can now consider the differences within the range and how it relates to the pavilion angles.
The Ideal Pavilion Angles
Marcel Tolkowsky who came up with the best angle for the pavilion facets and this was 40.75 degrees. The striking truth, however, is that even before the calculation of angles and before mathematics, diamond cutters were producing the most brilliant stones by cutting with this angle.
For years diamond cutters have used one rule and that is not to go beyond 41 degrees as this will be too steep.
Some diamond sellers with diamonds that are poorly cut often try to sell the idea that a cliff, that is 41 degrees is off. The truth is that light has a crucial angle beyond which light will leak. Instead of a cliff, what happens is that as the light rays leak out through the pavilion, there is a gradual transition from a strong light return to a weaker light return.
Keep in mind that this transition will occur at 41 degrees. It is therefore much safer for you to choose a diamond that is 40.75 degrees.
With diamond researchers now using light ray tracing, it is apparent that when the pavilion angle goes down to 40.5 degrees, there will be obstruction of light and even light leakage. The GIA will round off the 40.5-degree angles to 40.6 giving you between 40.6 and 41 degrees of pavilion angles to work with.
Anything between these two ranges can be considered acceptable angles for the pavilion.
The Shallow end of the Ideal Crown Angle
Between 34-35 degrees for the crown angle, there will be minimal light leakage. Note however that altering the crown angle will affect not just the brilliance of the diamond but the fire as well. This is because of its effect on the dispersion.
One of the factors that affect the dispersion is the angle of incidence while the light is leaving the diamond through the crown. Less light will be dispersed when the crown angle is shallower. This means that there is less fire in a stone that has a 34-degree crown angle than one with a 35-degree crown angle.
But what does this mean? If you are more interested in brilliance than fire, then you can go for a stone that has a crown angle that is near to 34 degrees. On the other hand, if you prefer a stone with more fire, then pick one with a crown angle closer to 35 degrees.
With more brilliance with a 34-degree crown angle, ensure that you pick a diamond that has a 41-degree pavilion angle. Also, make sure to check that the symmetry is ideal.
Something to be keen about is a diamond with a crown angle of under 32 degrees. This one will not be as durable as it has a sharp and wide girdle making it prone to chipping.
The Steep end of the Ideal Crown Angle
Generally speaking, when the crown angle is steep, this simply means that the crown sits higher and the crown facets are larger. The result is that they can take in more incident rays which will then be dispersed to produce more fire.
However, there is a trade-off as the girdle is more likely to leak light, especially when going above 35 degrees on the crown angle. This is the case even with a 40.8-degree pavilion angle. The reason is simply that the lower girdle angle is affected by the pavilion angle.
The steeper the pavilion angles the steeper the Lower girdle facet.
When the crown angle is very steep, this will reflect the light rays away from the observer. Looking down at the diamond, you might not see as much fire as someone standing next to you.
With a higher crown, there will be a lot of weight on the crown of the diamond. This will reduce the spread of the diamond and may make it look smaller than it is.
Some diamonds with an ideal cut will have a crown angle near 34.8 degrees. The result is that the diamond has plenty of fire. However, such a crown angle should be for a diamond that has a precise and quality cut. These diamonds are referred to as super ideals.
The Contrast Pattern
One more factor that is also affected by the crown angle is the contrast pattern. When you consider what we’ve been mentioning above, it’s very easy to believe that the crown angle has a huge impact on the overall appearance of the stone. The truth, however, is that its effect on a diamond’s face-up appearance is quite small.
When the crown is cut shallow, the weight of the diamond will be spread out and it will have a larger girdle. This makes it appear larger.
The arrow patterns which form with a shallower crown angle will have a shaft that is set very else to the arrowhead. On the other hand, with a steep crown angle, you may notice that the arrowhead is separated from the shaft.