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This feature is the diamond`s polish, it is also the only measurable feature which is independent to the formation process of the diamond but depends only on man made process and skill.


Important to know!

  • Polishing is the most important parameter influencing diamond appearance and reflectiveness.

  • It is better to buy a smaller diamond with better polish than a larger diamond with lousy polish.

  • The highest level of polish is known as triple EX or 3EX.

  • These facts and the entire article apply only to round diamonds.


Polish grade, also called diamond cut, doesn`t refer to the shape a diamond was cut (heart, round, square, ovale, etc.) but to reaching certain standards which combine to maximal light reflection.


In other words – better polish means better sparkle.

The key issue here is the measurement, and it relates to the low awareness within the population – in the past no one new how to measure this parameter and polish wasn’t that good either way. Research and modern technology today allowed the development of the field but the public haven`t closed the gap yet.


Polish grading scale from highest to lowest:

  • Excellent (aka EX)
  • Very good (aka VG)
  • Good
  • Fair
  • Poor


So what is polish practically? Because it is a fairly technical field and our goal is to provide information that will help you, we will try to give you a basic review. Round and non-round diamonds should be separated as you will see in this article.


Polish grading for round diamonds has three parameters:

Cut – the proportions between the different parts of the diamond. For example, the ratio between the height and diameter of the diamond, the width of the gridle, the table size, etc. In the optimal proportions, scientifically, the diamond should sparkle with all it`s might. This is the most important parameter in polish grading of a diamond because the proportions do matter. Diamond`s structure and proportions create three phenomena with different levels:


Brightness – refers to the external and internal white light that reflects off the diamond.


Fire – the separation of light to the rainbow colors while passing through the diamond.


Scintillation – the sparkle rate and the geometrical shapes that from the internal dark and lighter areas of the diamond.


Polish – there are some cases when the diamond is not sufficiently “brushed” and some areas are left rough.


The 1st reason is the need to reach a certain weight in order to stay in a certain price group. For example a diamond of 0.99 carat is much cheaper the 1 carat diamond.


The 2nd reason is that manipulation of some areas can revile internal defects or even damage the diamond. Either way, many diamonds doesn`t have perfect polish grade and most people won`t be able to differentiate. But in very low polish grade some areas will stay rough and the light flow inside the diamond will decrease.


Symmetry – plain and simple, is the diamond symmetrical or not in term of sides and its general shape. The easier parameter to evaluate with the naked eye is the diameter of the diamond. According to most the diameter is not completely equal and shift of few tenths of a millimeter are acceptable. Very low symmetry indicates weak proportions but a small lack in symmetry should not matter if its not visible to the naked eye. For those who want to take it one step farther and have the budget to invest in polish grade. Diamonds polish is important in regard to the size of the diamond (not talking about its weight).


For example, taking a diamond that weights 1 carat. It`s diameter may be 6 mm or 6.7 mm. In terms of appearance it is a huge difference (when dealing with such small objects). A stone weighting 1 carat with 6 mm diameter is called “pressed stone”. It is a stone which is either elongated or with wide girdle, etc. These stones don`t only have low polish grade they are also not cost-effective.


In the following image we see two diamond with high color grade (D-E), high clarity (VVS+) and equal weight. One of them has “good” cut grade and the other has “excellent” cut grade. Both stones have polish and symmetry grading as EX-EX. Its clear to see even due it is difficult to photograph diamonds that the stone with “excellent” polish grade is more life-like, bright and with no dark areas. In addition, the diameter of “excellent” diamond is longer by 0.2 mm – which is very significant in these diamonds. A stone weighting 1 carat and its diameter is 6.7 mm is called “pita”. It will reflect less light but has a great advantage – it looks much bigger and that might catch some people`s attention. It is clear that if the polish grade is low there is a preference of relatively flat diamonds that looks bigger rather than taller stones. The higher the polish grade of all parameters shows a skillful workmanship, scientific understanding and better working environment (for example, with no defect close to the surface or any attempt to reach a certain weight).


Why are the proportions of the diamond so important?

Polish grade is actually based on the interaction between the diamond`s sides and the rays of light passing through it. In general, every diamond has 58 sides (or 57 excluding the tip which is called “cullet”). Many proportions are measured aside of the diameter and height of the diamond.


For example, an important proportion is the pavilion depth which represents the distance between the gridle the the cullet. In case this proportion is too high or low, the rays of light won`t remain inside the diamond but will escape from its sides. In order to maximize light reflection, especially the visible light, it is recommended that the rays will leave the diamond through the crown – the upper part above the gridle. In a well proportional diamond, even the naked eye can recognize the darker and lighter parts are equal.


Tips for evaluating polish grade without accreditation

Dark-light – the darker and lighter areas should be of even size.

Wide gridle – when the gridle is relatively wide – stay back. You can recognize this by comparing a few diamonds to each other.

Touch – get a good feel of the diamond and make sure there aren`t any large rough areas, especially in its gridle.

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