Cut refers to the shape, faceting style, proportion and finish of a diamond. While “shape” is only known and described in many presentations, it’s the faceting style, proportion and finish that play a role in the “cut”.
Quick Background to Understand the Cut and the Cutting Process:
Diamonds are very, very old and where around almost dating back to the beginning of the Earth itself. Scientists believe the Earth was born some 4.65 billion years ago, the oldest diamonds crystallized around 3.3 billion years ago and the youngest diamond formed almost 1 billion years ago.
It does take some extreme conditions to form a diamond. The temperature ranges from 1,700 to 2,400 degrees Fahrenheit and the pressure needs to be around 650,000 to 8700,000 pounds-per-square-inch. These natural conditions to form diamonds are found 90 to 120 miles beneath the Earths surface. While not all diamonds were born at these depths, some were both even deeper inside the Earth and some diamonds were born on the surface using modern technology.
The ingredients have to be just right, 99.95% to 99.99% carbon making the diamond one of the purest of all materials found in nature and the only gem composed of one element.
Each carbon atom bonds with four neighbors to form the simplest and strongest of all three-dimensional formations, the tetrahedron. These form because the atoms share electrons and create a “covalent” bond. In many cases, the atoms that form a gem gain or lose electrons.
Brilliance:
The total intensity of color (or white light in a diamonds case) reflected from the gem's surface and interior. No other gemstone has more brilliance than a diamond.
Density:
The relationship between weight and size. This is determined by Specific Gravity (SG for short) which is the weight of a material vs. the weight of an equal volume of water. On this scale, a diamond weighs in around 3.52 which is 3.5 times greater than water.
Dispersion:
The splitting of white light in to spectral hues (rainbow effect). A diamond’s dispersion rate is 0.044 and is higher than any other natural gem but isn’t as high as Cubic Zirconia or synthetic Moissanite. Dispersion is the fire that talks to you from the diamonds heart.
Hardness:
Resistance to scratching. A diamond is the hardest known material and rates a 10 on the Mohs Hardness Scale. Tests show that a diamond is 140 times harder than a ruby or sapphire which rates a 9 on the Mohs Hardness Scale. But don’t get confused… a diamond isn’t indestructible.
Refraction:
The slowing and bending of light in a transparent material. The “refraction index” (RI for short) is the comparison between speed of light in the air and speed of light a material. The diamond rates a 2.417 which is 40% slower than air.
Scintillation:
The dance of bright reflections. Scintillation is that mesmerizing sparkle.
Toughness:
Resistance to breaking. The scale is “exceptional”, “excellent”, “good” and “fair”. A diamond rates a “good” on this scale because of cleavage.
Transparency:
The ability to transmit light and/or energy without blocking or distorting it. A diamond rates exceptionally well to visible light and energy from deep ultraviolet to infrared.
Parts, or Cuts of a Diamond:
Facet:
One of the flat polished surfaces cut on a gemstone or occurring naturally on a crystal.
Culet:
It's only purpose is to protect the sharp point from chipping (the bottom of an ice cream cone).
Star facet:
One of the eight small triangular facets in the crown of a brilliant-cut gem.
Girdle:
The edge of a cut gem held by the setting (a belt on a pair of pants).
Pavilion:
The lower surface of a brilliant-cut gem, slanting outward from the culet to the girdle.
Table:
A flat facet cut across the top of a gemstone.
French tip:
A facet configuration designed to increase the scintillation at the point of fancy brilliants.
The Meanings on Cut Quality:
Proportions:
Proportions are the relationships between the gemstone’s angles and parts.
Symmetry:
Symmetry is the precision and precise placement of each cut. Minor symmetry details may not be apparent but may affect the beauty.
Polish:
The smoothness and luster of a gemstone’s surfaces and reveals each gemstones potential.
Proportions, symmetry and polish when perfectly executed require sacrificing up to, or more than half of the gemstone’s precious weight but creating a beautiful finished gem. If these are not executed properly to save on weight loss then serious negative consequences will happen to the gemstone’s beauty.
Total Depth:
Depth in relation to its diameter and stated as a percentage.
Table Size:
The diameter of the table to the diameter of the girdle and stated as a percentage.
Crown Angle:
The angle formed by the bezel facets and the girdle which is stated in degrees.
Pavilion Depth:
The distance from the culet to the girdle and stated as a percentage of the girdle diameter.
Girdle Thickness:
The total width of the girdle surface from the upper girdle and lower girdle facets. The girdle thickness affects the final look of the gemstone and affects the resistance to chipping.
Culet Size:
The culet’s visibility judged face-up through the table under 10 x magnifications. If no culet is present then lower and the pavilion girdles won’t be protected and too large of a culet may create a “black spot” to appear through the table.
Cutting Formula's:
Total depth %depth / average girdle diameter x 100 = ________
Table Diameter %longest table measurement / average girdle diameter x 100 = ________
Different Types of Cut:
Fancy Cut:
They are based on width and not diameter and stated in a length(2)-to-width(1) ratio (2:1). Length-to-width ratio plays an important role in the fancy shape’s attractiveness.
Brilliant cut:
Brilliant cut refers to the "kite-like-shape" and triangular facets in a radial pattern. The brilliant cut can be applied to almost any cut style. The round brilliant is the oldest and most perfected cut.
Step cut:
Step cut refers to a trapezoidal shape of the cut creating a "flight-of-stairs" effect. One of the hardest, if not the hardest cut to make because the cuts have to be perfectly symmetrical and the gemstone has to be the best quality in order to have an attractive Step cut.
Mixed cut:
The combination of the Brilliant cut and the Step cut. They can be combined on the crown, pavilion or both.
It is very important to understand that when a cutter skimps on “cut” then the price of the diamond will be lower making the purchaser think they got an unbelievable deal.
Proportions shape the dynamics between the diamond and the light. Negative details, even so slight may not be apparent to the eye but could affect the beauty while being precise will enable the diamond to show every ounce of beauty.
A diamonds polish can reveal the diamonds potential. It makes the brilliance brighter and the scintillation memorizing.
Fun Fact:
Misuse of the words "brilliant" and "full cut":
It is unfair or deceptive to use the unqualified expressions "brilliant," "brilliant cut," or "full cut" to describe, identify, or refer to any diamond except a round diamond that has at least thirty-two (32) facets plus the table above the girdle and at least twenty-four (24) facets below.
Note to § 23.16:
Such terms should not be applied to single or rose-cut diamonds. They may be applied to emerald-(rectangular) cut, pear-shaped, heart-shaped, oval-shaped, and marquise-(pointed oval) cut diamonds meeting the above-stated facet requirements when, in immediate conjunction with the term used, the form of the diamond is disclosed.
Cut Make and Names:
Round Brilliant:
A Round Brilliant is the most popular cut and the most comfortable cut to be purchased by consumers from all corners of the world. A Round Brilliant maximizes brilliance, dispersion and scintillation.
The make of the Round Brilliant is as follows:
1 - Table
8 - Bezel facets
8 - Star facets
16 - Upper girdle facets
16 - Lower girdle facets
8 - Pavilion main facets
1 - Culet (pronounced - KYOO-let)
The total facets must be 57-58 depending on the culet -or- no culet.
Fancy Cut:
Any shape besides the round brilliant is considered a "fancy shape" or "fancy cut". The traditional fancy cuts are as follows:
Marquise (pronounced mar-KEEZ or mar-KEE)
Emerald cut
Oval cut
Heart shape
Princess cut
Pear shape
Oval cut
Radiant cut
Trilliant
Royal Asscher
Quadrillion
Hearts and Arrows
Hearts on Fire...and more
Bow-Tie Effect:
(Oval cut, Pear shape, Heart shape, Marquises) Many fancy shape brilliants often will have combinations of crown and pavilion angles that create a dark reflection at the Table’s mid-section seen from top down with no magnification.
Diamond cutting involves a number of separate processes because hardness differences exist within every diamond. The underlying principle is to cut away the softer parts of diamonds using the harder parts of other diamonds.
In many diamond cutting and diamond polishing techniques diamond dust from non-diamond-quality diamonds is used to grind or polish gem-quality diamonds. The microscopic scratching wears away the crystal to leave an unsurpassed polish on the gem-quality diamond.
Planning the Cut:
The main objective of the cutter is to produce the maximum value from every diamond rough as possible. The means transforming the natural features of the diamonds crystal into the best combination of the 4c’s in the finished gemstone.
Weight:
It’s important to capture as much diamond weight as possible or at least cut to the market, like 1/2, 3/4, and 1 carat.
Clarity:
Properly cutting the diamond crystal to eliminate inclusions or at least positioning them for minimum visible result in the highest grade. The diamonds crystal structure becoming distorted will cause graining, fractures and cleavage breaks. In some rare cases, inclusions can be other diamond crystals or other minerals engulfed by a growing diamond. The diamonds crystal structure will dictate to the plotter how the diamond will be shaped.
Color:
Diamonds in the near-colorless to colorless range planning isn’t pain-staking but fancy colored crystals are carefully oriented to display the most color.
Diamond Shape:
In many cases round brilliants are fashioned but when the rough is distorted usually fancy cuts will be produced.
Crystal Structure:
Also known as “grain”. Cutting across the grain produces a smooth cut while cutting with the grain will produce a rough and even splitting cut.
Light Behavior:
Cutting the diamond in the best way to achieve the most beauty (brilliance, dispersion, and scintillation). Sometimes the cut is slightly off to capture more diamond weight but significant variations will hurt the overall visual appeal of the diamond.
Dividing the Crystal:
Before shaping and polishing many rough crystals are divided at least once. Some crystals go through many divisions to reach a suitable diamond-size.
Cleaving:
Cleavage is the potential to beak in a certain direction inside the crystal and is one of the diamond’s inherent properties. Cleaving is the easiest yet probably the oldest of all techniques to divide a crystal into two parts.
Mechanical Sawing:
A technique that first started with a metal wire and a bowed wooden handle (which took many days to divide a diamond) and then modern technology came into play with a rotary blade powered by an electric motor. Both techniques needed a toothless cutting device and a lot of olive oil mixed diamond grit.
Laser Sawing:
A computer that uses a high-intensity laser that will cut a diamond’s pattern once it is given the dimensions from a technicians program. This technique saves time over mechanical sawing, but can sacrifice diamond weight. The benefits to laser sawing are: keeps labor down, virtually eliminates “graining” restrictions, and can easily cut novelty shapes that are hard to do with conventional methods.
Fun Fact:
One BIG Rock:
The Centenary Diamond, a modified Heart-shape, weighs 273.85 carats and is the world’s third largest high clarity, high color diamond. It features 247 facets and took years to plot and cut.