What else affects cut grade besides facet proportions?
Apart from the proportions (the most critical factor), there are 4 other factors that make up the overall cut grade of the diamond.
The girdle is the outermost surface of the diamond and main purpose is to prevent chipping during the setting process. Depending on the shape of the diamond, the ideal girdle thickness can vary. In round diamonds, a thin-medium girdle thickness is preferred.
However, when it comes to fancy shapes, a girdle thickness of thin to very thick can be justifiable. This is especially true if the shape consists of sharp points which are vulnerable to damage. For example, the 4 corners of a princess cut are very susceptible to chipping and requires a thicker girdle thickness to ensure better durability.
The girdle thickness is taken into account for a stone’s cut grade based on 2 reasons.
1) A very thick girdle will result in a smaller diameter of the stone because of the extra weight hidden in the girdle area.
2) A very thin girdle subjects the stone to additional risks of chipping and causes it to be penalized for durability reasons. As a result, the overall cut grade takes a hit.
In general, a diamond can have a girdle finishing which falls under one of the following:
Faceted – Cut and polished facets.
Polished – Clear or see through.
Unfaceted, or Bruted – Left in its original rough state.
The majority of diamonds you see in today’s market either have a faceted or polished girdle. Personally, I prefer either a faceted girdle as it gives the stone a more complete look. On top of that, it can help mask flaws found in the vicinity of the girdle. Interestingly, the type of girdle finishing has no impact on the clarity and cut grade.
The culet is the pointed tip where the pavilion mains meet. Sometimes, the culet is polished off and the sole purpose of doing this is to protect the tip from breaking or chipping. When you are reviewing a grading report, you should choose a diamond with culet size between None (best), Very Small.
A culet size larger than small can easily be seen and often mistaken to be inclusion.
Symmetry basically refers to how consistent a diamond’s facets are polished to. If there are some misshapen facets, it can set off a chain effect which affects surrounding facets. Symmetry is also a measure of how precise each individual facets align in relation to each other.
A diamond with poor symmetry may misdirect light that travels through the diamond, sending it off at slightly wrong angles, and thereby reducing the diamond’s brilliance.
Here’s an interesting fact: Symmetry flaws are often created by design and not as a result of incompetent cutting skills. Most symmetry flaws are introduced on purpose during the polishing process. For example, an extra facet may be polished into the diamond’s surface to remove an inclusion in order to acheive a higher clarity grade.
1. The table or culet being very slightly off-center.
2. Unequal sizes of opposing facets.
3. Misshapen facets.
4. Wavy girdles.
5. The table not being parallel to the girdle.
6. Pavilion and crown facets are out of alignment.
Since a diamond with poor symmetry may cause problems with light performance and can adversely impact the overall outline, my recommendation is to stick with a Very Good or Excellent grade for round diamonds.
Very Good Symmetry
Can you tell the differences between the 2 stones? One of them has unequal looking lobes while the other showcases a pleasing shape.
For fancy shapes, I recommend choosing diamonds with at least a Very Good symmetry grade. Fancy cut diamonds with Good symmetry grades need to be examined on a case by case basis and shouldn’t be automatically discounted.
That said, fancy shaped diamonds are a little more tricky to select. Bear in mind you do require additional data like photographs or videos in order for you to perform critical examinations.
Polish refers to how smooth the diamond’s surface is and it is responsible for giving the diamond its sheen and luster. During the cutting process, a rough diamond is placed on a spinning turntable and each facet is added one at a time.
A high quality polish will not leave any visible marks or scratches and creates a smooth planar surface ideal for light transmission.
On the other hand, poor polish will result in a lackluster appearance due to the presence of marks that can blur the diamond’s surface. On a microscopic level, these grooved surfaces can cause undesirable diffusion of light rays and hinder optics.
Even under 10X, polish lines for a Good grading is not easily detected by the untrained eye.
With that said, there is no need to get carried away and buy only diamonds with Excellent polish ratings. In real life, the differences between a very good and excellent polish are almost undetectable to the naked eye. My recommendation is that you should not choose a diamond with a polish below Very Good.
By now, I hope you have a better idea about the various elements that contribute towards a diamond’s cut. If you have further questions, feel free to leave a comment below. On the next page, I will show you how to determine a diamond’s optics rationally and highlight insights that a certificate doesn’t tell you…