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Diamond Cut
Carat Weights

Diamond-Cut – The most important of the 4C’s

Diamond-Cut is the most important aspect in determining a diamond’s beauty and is the most difficult for the consumer to judge when shopping for a diamond. It is the only factor controlled by man and for many years it has been the least understood by the consumer. The cut of a diamond is the arrangement of its facets, as well as the finish and proportions of a diamond. You can have a high color or/and clarity of a diamond, but if the cut is poor, it will not shine the way you want it. Fancy shapes are a preference in the cut, these are difficult to grade, as it is personal taste. Some people will try to tell you there is a grade but fancy shape diamonds are a personal preference. Example: Some like a long skinny Marquise but there are some like a fat squatty Marquise, neither one is less valuable than the other.

The Diamond Cut grade is the biggest change in the diamond industry in the last 30 years. Be wary of “Speciality Cuts” they are marketed to be special but most are nowhere near the amount you pay when you go to resell the stone.

A highly trained diamond cutter must first analyze a rough diamond before considering what diamond cut will complement the natural beauty of the stone. Interestingly, a diamond can only be cut by another diamond.

How Important is the Cut of a Diamond?

It is possible to have two diamonds that are equal in carat size, share the same color and clarity but look completely different. It all depends on the cut. Based on the cut, the weight of the diamond can be distributed differently to various parts of the diamond such as the crown and girdle. Also, the way facets are arranged and how brilliant the diamond appears will be determined by the way the diamond is cut. The diamond can have lower clarity and color but still shine as it is the cut of the stone that makes it sparkle.

Diamond-Cut Grading

Certified diamonds are anywhere from 20% to 60% more than non-certified stones. Stones under .18ct are normally not certified by GIA or AGS. 90% of the diamonds you see in jewelry stores and online are non-certified stones. Unless they say they are GIA or AGS and have documentation to back it up. There is nothing wrong with non-certified diamonds, they are less money and can be just as beautiful.

In 2005, the GIA introduced its ‘Diamond Cut Grading System’ for round brilliant diamonds. This system has been in development for fifteen years and the researchers at GIA have been perfecting a computer modeling system for round brilliants. They experimented with more than 70,000 stones in order to successfully establish this new grading system. The result of the research is that the system can now predict the cut grade for millions of various sets of round brilliant diamonds. This new ‘Diamond Cut Grading System’ analyzes the diamond’s face-up appearance by using many different computer modeling techniques in addition to algorithms, which are used to evaluate the levels of brightness, fire, and scintillation.

GIA is not an appraisal; it is a birth certificate to the diamond that gives you the information of the inclusions, cut, polish, symmetry ECT… of the diamond. No two diamonds are alike.

The science supporting the AGS Lab’s cut grade system is the result of years of research, testing, and retesting by a team of gemologists, optical physicists, and mathematicians. In the AGS cut grade system, all facets of a diamond are measured in three dimensions rather than two dimensions. The AGS Lab uses state-of-the-art ray-tracing software to trace light traveling through a diamond. The software demonstrates the quantity and quality of the light being returned to the viewer. AGS Laboratories will now consider brightness, dispersion, leakage, contrast, and weight ratio, in addition to proportion, symmetry, and polish, when assigning a final cut grade.

Scale
GIA Excellent Very Good Good Fair Poor
AGS 0 1 2 3 4 5 6 7 8 9 10

*Since GIA and AGS Labs use different scales and methods, this represents Eye for Gems’ opinion as to the equivalence of the two grading systems.

GIA, AGS and the New Cut Grading: The Metrics

The GIA Cut scale levels are: Excellent, Very Good, Good, Fair and Poor. The GIA Cut grade assesses the diamonds in these primary ways:

Face-Up Appearance is the most important part of GIA’s cut grade assessment.

  • Brightness: Usually referring to the “brilliance” of a stone.
  • Fire: Display of colored light return as observed in stronger lighting conditions.
  • Scintillation: Movement of the light’s pattern within the diamond as the diamond observer or light source is moved.

Diamond Physical Design

  • Weight Ratio: Refers to the appearance of the size of the diamond in relation to its weight. i.e., diamonds cut too deep appear to be smaller than their intended weight.
  • Durability: Refers to the possibility of the diamond chipping or breaking due to extremely thin girdles. GIA did not find evidence that a diamond’s durability suffered from shallow angles unless the girdle was very thin.

Diamond Craftsmanship

  • Polish: Quality of the finish ultimately affecting luster.
  • Symmetry: Facet placement and their alignment with adjoining and opposite corresponding facets.

Diamond Brilliance

The arrangement of a diamond’s facets (a key part of how a diamond is cut) determines the sparkle and brilliance of the stone. Facets of a diamond can be flat, angular, or surface plains. A diamond that is poorly-cut will lack sparkle and a diamond that is well-cut can compensate for a small size or imperfect color or clarity.

Depth and Width

The depth and width of the stone can affect the way light travels within the diamond and how it leaves the diamond, which directly impacts a diamond’s brilliance. For example, if the diamond is too shallow, then the light is lost through the bottom of the stone and causes a loss of brilliance. If it is too deep, then light escapes from the sides and creates a dark and dull appearance.

Brightness, Fire, and Scintillation

The goal in extracting the most beauty from the diamond is to have the light enter the stone and disperse as it bounces inside the stone through the different facets and produces sparkle and flashes of brilliant color. While doing this, the diamond should return as much light to the eye as possible.

Anatomy of the Diamond

The cut of the diamond is determined by the anatomy of the diamond. The composition of the diamond is made up of diameter, table, crown, girdle, pavilion, culet, and depth.

  • Diameter: Width of the stone that is measured through the girdle
  • Table: The largest facet of a diamond, which is on top of the stone
  • Crown: Top part of the diamond that extends from the girdle to the table
  • Girdle: Defines the perimeter of the diamond as it intersects the crown and pavilion
  • Cut: Facet at the tip of the diamond.
  • Depth: Height measured from the culet to the table

Diamond Refraction

Another process by which cut has a direct effect on how much light enters the diamond, and how brilliant the diamond will become, is a process called refraction. The brilliance of diamonds results from their high refractive index, a measure of how strongly a transparent material bends light rays. The key to a diamond’s brilliance is that diamonds tend to bend light more so than any other natural substance.

Diamond Polish

Polish affects how light is able to pass through a diamond and is very important to a diamond’s brilliance. You should only select a diamond that is laboratory certified with good, very good or excellent polish.

Diamond Symmetry

Symmetry is an important element of a diamond’s finish. Symmetry refers to the size, alignment, and matching of the individual facets. You should only select a diamond that is laboratory certified with good, very good or excellent symmetry.

GIA, AGS and the New Cut Grading: The Metrics

The following is a summary of individual metrics used by each lab for cut grading.

GIA Metrics

The GIA Cut scale levels are: Excellent, Very Good, Good, Fair and Poor. The GIA Cut grade assesses the diamonds in these primary ways:

Face-Up Appearance is the most important part of GIA’s cut grade assessment.

  • Brightness: Usually referring to the “brilliance” of a stone.
  • Fire: Display of colored light return as observed in stronger lighting conditions.
  • Scintillation: Movement of the light’s pattern within the diamond as the diamond observer or light source is moved.

Diamond Physical Design

  • Weight Ratio: Refers to the appearance of the size of the diamond in relation to its weight. i.e., diamonds cut too deep appear to be smaller than their intended weight.
  • Durability: Refers to the possibility of the diamond chipping or breaking due to extremely thin girdles. GIA did not find evidence that a diamond’s durability suffered from shallow angles unless the girdle was very thin.

Diamond Craftsmanship

  • Polish: Quality of the finish ultimately affecting luster.
  • Symmetry: Facet placement and their alignment with adjoining and opposite corresponding facets.

AGS Metrics

The AGS Cut scale levels run from 0 for ‘Ideal Cut’ to 10 for ‘Poor’. Because the AGS bases their cut grade on light performance this allows them to grade for shapes other than round. The AGS Cut grade assesses the diamonds in these primary ways:

Diamond Anatomy

Purchasing a diamond is one of the most exciting and expensive investments you will make so it is best to educate yourself about the physical properties of a diamond, particularly the anatomy, As your knowledge about the physical attributes of a diamond grows, so does your ability to purchase the best possible diamond as well as stay within your budget.

Light Performance

  • Brightness: Usually referring to the “brilliance” of a stone
  • Dispersion: The appearance of colored light return through the crown in conditions that enhance the metric.
  • Leakage: Facets which are functioning in the role of “window” rather than “mirror” or “non-reflector” as opposed to a “reflector”.
  • Contrast: The light and dark patterns seen when observing a diamond. It can produce a positive or negative optical effect. This usually is caused by, but not limited to, the observer’s head.

Diamond Proportion Factors

  • Tilt: Not only is the face-up view considered but tilting the stone to examine its optics are considered.
  • Durability: Refers to the possibility of the diamond chipping or breaking due to extremely thin girdles.
  • Weight Ratio: Refers to the appearance of the size of the diamond in relation to its weight. i.e., Diamonds cut too deep appear to be smaller than their intended weight.
  • Girdle thickness: too thin or too thick is not considered desirable
  • Culet Size: must not be chipped or too large.

Diamond Finish

  • Polish: Quality of the finish ultimately affecting the luster
  • Symmetry: Display of colored light return as observed in stronger lighting conditions

Optical Characteristics/Metrics

The optical characteristics of a diamond determining light performance and appearance.

  • Contrast: If a stone returns light so that the crown is bright all over, it would not appear as bright to your eye as one with good contrast. While the light return is an important part of ‘brilliance’, our perception of brightness is enhanced by our eyes adapting to contrasting backgrounds. Diamonds with good contrast, caused by alternating very bright and very dark facets, appear brighter because of perception and physiology of the way the eye works.
  • Brightness: Usually referring to the “brilliance” of a stone
  • Fire/Dispersion: The appearance of colored light return through the crown in conditions that enhance the metric
  • Scintillation: Movement of the light’s pattern within the diamond as the diamond, observer, or light source is moved.
  • Leakage: Areas of a diamond that do not return light towards the eye usually due to the light leaving the pavilion side of the diamond.

According to GIA

A polished diamond’s beauty lies in its complex relationship with light: how light strikes the surface, how much enters the diamond, and how, and in what form light returns to your eye. The result is a display of three attributes. Brightness is the combination of all white light reflecting from the surface and interior of a diamond. Fire is the colored flashes that can be seen in a diamond. Scintillation describes the sparkle of light you see in a diamond, and the overall pattern of bright and dark areas when you look at a diamond face-up.

A diamond is attractive when it is bright and fiery; when it has a pleasing, even pattern to its areas of light and dark (scintillation); and when it demonstrates a high level of craftsmanship. A diamond is less attractive if it is dark; if it is not fiery; if it has a distracting or unpleasant pattern; if it is carelessly polished; or if it is sloppily cut. Also, a diamond with a too-thin girdle may be attractive, but it is more susceptible to damage. A diamond with a thicker girdle or a larger total depth also can be attractive, but then the customer pays for unnecessary weight.