A diamond carat weight (ct.) is a unit of measurement used in the diamond industry to determine the size and weight of a diamond. One carat is equivalent to 200 milligrams or 0.2 grams.  

The word "carat" comes from the Greek word "keration," which was a unit of measurement, equivalent to the weight of one carob tree seed (also called a carob bean). The ancient merchants used these seeds as a reference for weighing diamonds and other precious stones, as their uniform size and weight made them a convenient and reliable standard of measure. Over time, the word "keration" evolved into the word "carat," which is now widely used as a unit of measurement for diamonds and other gems.  

As the carat weight of a diamond increases, its price generally also increases. This is because larger diamonds are rarer and more sought after than smaller diamonds, so they are considered more valuable. However, the price increase is not proportional to the carat weight, meaning that the price of a 2.00 ct. diamond is not exactly twice the price of a 1.00 ct. diamond, but rather more. This is called a diamond carat weight price premium. It is an increase in the price of a diamond due to its carat weight. As a diamond's carat weight increases, so does its rarity and perceived value, leading to a higher price. The price premium is the amount by which the price of a diamond increases as its carat weight increases. For example, a 1.00 ct. diamond may cost $5,000, while a 2.00 ct. diamond of the same quality may cost $20,000. The price premium in this case would be $15,000, or the difference in price between the two diamonds. The price premium is not always a linear increase, and the exact amount can vary depending on factors such as the quality, color, clarity, and cut of the diamond. However, in general, diamonds with larger carat weights will command a higher price due to the diamond carat weight price premium.  

Also, the price of a diamond can increase significantly at certain "carat weight jump boundaries," which are points at which the carat weight increases by a whole number. For example, the price of a 1.99 ct. diamond may not be much higher than the price of a 1.95 ct. diamond, but the price of a 2.00 ct. diamond may be significantly higher. These jump boundaries often result in higher prices because the demand for diamonds of a particular size is often higher, which can drive up the price. The most noticeable carat weight jump boundaries are at 1.00 ct., 1.50 ct., 2.00 ct., 2.50 ct., 3.00 ct., etc..

When buying diamonds, a common practice is to "buy shy". This refers to the practice of purchasing a diamond that is slightly below a full carat weight or other significant weight boundary in order to save money on the purchase. For example, instead of buying a 1.00 carat diamond, a buyer might opt to purchase a 0.90 carat diamond that is slightly below the weight boundary.  The practice of buying shy can be a very good way to purchase a diamond that still looks beautiful and substantial, while saving money on the purchase. This is because diamonds that are just below weight boundaries can often be priced significantly lower than diamonds that meet the weight boundaries, even though the visual difference may be minimal or imperceptible. 

The words "carat" and "karat" are not the same. "Carat" is a unit of measurement used in the diamond industry to determine the size and weight of a diamond, while "karat" is a unit of measurement used to indicate the purity of gold. One carat is equal to 0.2 grams, while a karat is equal to 1/24 part of pure gold in an alloy. For example, 24-karat gold is pure gold, while 10-karat gold contains 10 parts gold and 14 parts other metals.

Carat weight

The shape of a diamond refers to the resemblance of the diamond to a specific geometric shape when viewed from the top. The shape of a diamond can affect its brilliance and overall appearance. It is the final product of the diamond cutting process. Current diamond shapes are based on centuries of diamond cutting experience and scientific research. The most common shapes are round, princess, cushion, and pear. Other common shapes include marquise, oval, and heart. But nowadays, there are no limits to the variety of diamond shapes.

Round is the most popular diamond shape. The reason for its' popularity is the diamond appearance. A round shape provides the best conditions for a diamond to present its' brilliance and fire when looked at from the top. Diamond brilliance refers to the amount of light that is reflected and dispersed from the surface and interior of a diamond. Diamond fire refers to the visual phenomenon of the rainbow-like colors that are dispersed from a diamond when it is exposed to light. Current round brilliant-cut has been originally developed in year 1919. There were small updates since then and currently, a round brilliant-cut diamond has 58 facets (or 57 if the culet is excluded).

Oval shape is a modified round brilliant-cut. Current oval diamond shape has been created in 1960's. This shape produces almost as much brilliance and fire as a round shape. It is popular due to its' similarity to the round shape, but with a extra touch of extravagance. It is usually saught after by customers, who already have a round shaped diamond or like the look of a round cut diamond, but want to try something different.

A cushion cut diamond is a type of diamond cut that features rounded corners and larger facets, giving the diamond a shape that resembles a cushion or a pillow. This cut style has been popular for over a century and is known for its soft, romantic appearance and its ability to display a good amount of fire. Cushion cut diamonds often have a square or rectangular shape, with rounded corners, and a small table and deep pavilion, which can give the stone a vintage or antique look.

The pear shape is a combination of a round shape and a marquise shape. If it is worn on a hand, this diamond shape should be worn with the sharp end always pointing to the wearer's fingertips. This shape is also popular in earring designs or necklaces, where it is worn with the sharp end pointing upwards.

The emerald cut diamond is a rectangular shape with cut corners, and step-cut faceting on the pavilion and crown. This shape of diamonds has been previously used to cut emeralds, hence the name. It has a sleek, elongated appearance and is often used to highlight the clarity of the diamond. While it doesn't have the brillinace and fire of a round cut, the emerald shape produces a hall-of-mirrors effect meaning internal reflections of light that occur within the diamond. It is seen as a series of reflections, similar to mirrors placed opposite each other, creating an illusion of depth and enhancing the brightness and fire of the diamond.

The Asscher cut diamond is a square shape with cut corners and a distinctive, stepped pattern of facets. It has a high crown, deep pavilion, and small table, which give it a unique, vintage appearance. The Asscher cut diamond was invented by the Asscher Brothers, Joseph and Abraham, who were diamond cutters and polishers based in Amsterdam, Netherlands in the early 20th century, who were also famous at the time for cutting the largest rough diamond - th Cullinan with its' 3,106.75 carats. The Asscher cut is often referred to as a "square emerald cut" and is known for its stunning optical symmetry, creating a mesmerizing effect of parallel lines and flashing facets. The Asscher cut diamond was invented by the Asscher Brothers, Joseph and Abraham, who were diamond cutters and polishers based in Amsterdam, Netherlands in the early 20th century. 

The heart shaped diamond is a popular and romantic diamond cut, symbolizing love and affection. It is a combination of a round and pear shape, with a rounded bottom and a cleft at the top. The heart shape is created by carefully cutting and polishing the diamond to create a symmetrical and well-proportioned shape that resembles a heart. The heart shape diamond is often used for engagement rings, pendants, and other jewelry items, and is considered one of the most unique and sentimental diamond cuts.

The marquise diamond is a boat-shaped diamond cut with pointed ends. It is known for its elongated shape that can make fingers appear slimmer and longer. The marquise diamond shape is named after the French King Louis XV's mistress, Madame de Pompadour. Legend has it that the King commissioned a diamond cutter to create a diamond that would resemble the shape of her lips, which he considered to be the most beautiful in the world. The result was the marquise diamond, which has since become a popular choice for jewelry.

The princess diamond is a square or rectangular diamond cut with pointed corners. It is one of the most popular diamond cuts for engagement rings and is known for its modern and elegant look. The princess cut has pointed corners and its sides are usually cut with a series of diagonal lines that give the diamond its signature sparkling appearance. It has a high level of brilliance and fire due to its many facets and can provide a larger surface area for light to reflect compared to other diamond shapes.

The radiant diamond is a rectangular diamond cut with cut-off corners, giving it a more rounded appearance than the princess cut. It has a combination of the brilliance of a round cut diamond and the angularity of an emerald cut diamond. The radiant diamond has 70 facets and its cut-off corners help to minimize the appearance of inclusions and enhance the overall sparkle of the diamond.

Shape

The Gemological Institute of America (GIA) uses a grading system to evaluate the color of diamonds, with the grades ranging from "D" (colorless) to "Z" (light yellow or brown). 

The color grades are based on the absence of hue, with "D" being completely colorless and "Z" having a noticeable yellow or brown tint. The following is a summary of the GIA diamond color grades:  
- D, E, F: Colorless 
- G, H, I: Near Colorless 
- J, K: Faint Yellow 
- L, M: Very Light Yellow 
- N-Z: Light Yellow/Brown 

To determine a diamond's color grade, the GIA compares it to a set of master stones under controlled lighting and viewing conditions. The grading process is done by highly trained gemologists who evaluate the diamond's hue, tone, and saturation.  The first set of reference master stones for diamond color grading were created by the Gemological Institute of America (GIA) in the 1950s. The GIA is one of the world's leading gemological organizations, and it is widely recognized as the authority in diamond grading and certification.

Color

Diamonds have different clarity because of the presence of internal imperfections (inclusions) and external imperfections (blemishes).  These inclusions and blemishes occur naturally as the diamond forms in the earth's mantle over millions of years. The specific location, size, number, and type of inclusions and blemishes in a diamond can vary greatly from one diamond to another, resulting in differences in clarity. 

Inclusions are defects that are within the diamond's crystal structure, such as bubbles, cracks, or mineral deposits. Blemishes, on the other hand, are surface imperfections such as scratches, chips, or nicks.  

The clarity of a diamond is evaluated using a set of standard clarity grades. The grades range from "F" (Flawless) to "I" (Included) and describe the visibility of inclusions and blemishes to the naked eye. Diamonds with higher clarity grades are considered to be more valuable because they have fewer visible inclusions and blemishes.

Clarity grades:
1. Flawless (Fl): No inclusions or blemishes are visible under 10x magnification.
2. Internally Flawless (IF): No inclusions are visible under 10x magnification, but some surface blemishes may be present.
3. Very, Very Slightly Included (VVS1 and VVS2): Inclusions and blemishes are difficult to see even under 10x magnification. The difference between VVS1 and VVS2 is the visibility of inclusions and blemishes. A VVS1 diamond has inclusions and blemishes that are extremely difficult to see, even under close inspection, while a VVS2 diamond has inclusions and blemishes that are slightly more noticeable.
4. Very Slightly Included (VS1 and VS2): Inclusions and blemishes are visible under 10x magnification but are not noticeable to the naked eye. The difference between VS1 and VS2 is the visibility of inclusions and blemishes. A VS2 diamond has inclusions and blemishes that are slightly more noticeable under close inspection than a VS1 diamond, but both grades are considered to have similar levels of clarity.
5. Slightly Included (SI1 and SI2): Inclusions and blemishes are visible under 10x magnification and may be visible to the naked eye. The difference between SI1 and SI2 is the visibility of inclusions and blemishes. A SI1 diamond has inclusions and blemishes that are less noticeable to the naked eye compared to a SI2 diamond, but both grades have similar levels of clarity under close inspection.
6. Included (I1, I2, and I3): Inclusions and blemishes are visible to the naked eye and can affect the appearance and durability of the diamond. The difference between I1, I2, and I3 clarity grades is the visibility and number of inclusions and blemishes in the diamond. An I1 diamond has inclusions and blemishes that are noticeable to the naked eye, while an I2 diamond has inclusions and blemishes that are even more noticeable. An I3 diamond has inclusions and blemishes that are highly visible and affect the overall appearance of the diamond.

Clarity

The cut of a diamond refers to how well the diamond has been cut and shaped to bring out its brilliance (the amount of light that is reflected from the surface and interior of a diamond), fire (the rainbow of colors that is seen within a diamond, produced by the dispersion of light into its spectral colors) and scintillation (the sparkle or flash of light that is produced when a diamond is moved or when light enters and exits the diamond's surface). 

A well-cut diamond will have a good balance of "fire" and "brilliance" . A poorly cut diamond may appear dull or have a dark center.  When a diamond cutter plans to cut a rough diamond, he is balancing between ideal the cut proportions, maximum carat weight and the specific diamond properties (for example internal inclusions in the diamond) in order to produce the highest yield from the rough stone.  On average, a diamond can lose anywhere from 50% to 80% of its rough weight during the cutting process. For example, a round brilliant diamond typically loses about 50% of its weight, while a more complex shape, such as an emerald cut, can lose closer to 60% or more.  

When it comes to the appearance of a diamond's weight, the cut can also have a big impact. A diamond that is well-cut for its weight will look larger and more impressive than a poorly cut diamond of the same weight. This is because a well-cut diamond will have a better balance between the crown, pavilion, and girdle, which allows for more light to enter and reflect back out, creating a brighter and more sparkling appearance.  So, while carat weight is one factor that affects a diamond's appearance and price, the cut is also an important consideration. When selecting a diamond, it's important to find the best balance between carat weight and cut to achieve the desired appearance and value.

Diamond polish refers to the quality of the surface finish of a diamond's facets. 

By polishing a diamond, its surface is smoothed, and the number and placement of the facets can be optimized to reflect and refract light in a way that maximizes the diamond's fire, scintillation, and overall beauty. The polish grade reflects how well the diamond cutter was able to polish each facet, removing any surface imperfections and ensuring that the surface of the diamond is smooth and reflective. 

Diamond polish is usually graded on a scale from Excellent to Poor, with additional categories such as Very Good, Good, and Fair. An Excellent or Very Good polish grade indicates that the diamond has a high level of reflective brilliance and is free of any visible polishing lines, scratches, or nicks. A Good or Fair polish grade may have some slight surface imperfections, which can reduce the diamond's reflective brilliance.

Polish grades:
1. Excellent (EX): This is the highest polish grade and indicates that the diamond has an extremely high-quality surface finish with no visible blemishes or marks on its facets.
2. Very Good (VG): This grade indicates that the diamond has a very good surface finish with only minor blemishes or marks visible on its facets under 10x magnification.
3. Good (G): This grade indicates that the diamond has a good surface finish, but some blemishes or marks may be visible on its facets under 10x magnification.
4. Fair (F): This grade indicates that the diamond has a fair surface finish, with some visible blemishes or marks on its facets under 10x magnification.
5. Poor (P): This is the lowest polish grade and indicates that the diamond has a poor surface finish with many visible blemishes or marks on its facets under 10x magnification.


It's important to note that the polish grade is just one of the many factors that determine the overall quality and value of a diamond. Other factors such as the diamond's cut, color, and clarity are also important considerations when evaluating a diamond.

Polish

Diamond's symmetry encompasses a number of different factors, including the angles and proportions of the diamond's facets, the alignment of those facets, and the overall balance of the diamond's shape. The symmetry of a diamond can greatly affect the diamond's beauty, as it determines how light is reflected and refracted within the diamond. A diamond with an excellent symmetry will have a balanced and even pattern of light and dark areas, with no visible variations or imperfections in its cut.  

The Gemological Institute of America (GIA) diamond symmetry grading system evaluates the alignment, shape, and placement of a diamond's facets, as well as the overall balance and symmetry of its appearance. The GIA grades diamond symmetry on a scale from Excellent to Poor.  

Symmetry grades:
1. Excellent: The diamond has very precise and symmetrical facets, with a high level of fire and brilliance.
2. Very Good: The diamond has minor variations in symmetry that are only visible under magnification, but still has a high level of fire and brilliance.
3. Good: The diamond has some visible variations in symmetry, but still appears symmetrical to the naked eye, and has a good level of fire and brilliance.
4. Fair: The diamond has visible variations in symmetry that may affect its appearance and light performance.
5. Poor: The diamond has significant variations in symmetry that result in a reduced level of fire and brilliance, and a less attractive appearance.


When evaluating a diamond's symmetry, the GIA looks at various factors, including the alignment and shape of its facets, the evenness and consistency of its girdle outline, and the overall balance and symmetry of its appearance. The GIA diamond symmetry grade can have an impact on the overall value and price of a diamond, with higher symmetry grades indicating greater beauty and value.

Symmetry

Diamond fluorescence is the phenomenon where a diamond emits a visible glow when exposed to ultraviolet (UV) light. The most common cause of diamond fluorescence is the presence of nitrogen atoms in the crystal structure, although other impurities such as boron or hydrogen can also cause fluorescence.  

Fluorescence can range from "None" to "Very Strong," and can affect the appearance of the diamond in different ways.

Fluorescence grades:
1. None: No fluorescence is visible under UV light. This is considered the most desirable fluorescence grade, as it does not affect the diamond's appearance.
2. Faint: A very small amount of fluorescence is visible under UV light. It has no significant impact on the diamond's appearance.
3. Medium: A moderate amount of fluorescence is visible under UV light, but it has little impact on the diamond's appearance.
4. Strong: A significant amount of fluorescence is visible under UV light and can have a slightly hazy or oily appearance.
5. Very Strong: A very intense fluorescence is visible under UV light and can have a noticeable impact on the diamond's appearance, making it appear hazy or cloudy.


Some diamonds have a very weak fluorescence that is barely noticeable, while others have a strong fluorescence that can make the diamond appear hazy or milky under certain lighting conditions.  In general, diamonds with a strong fluorescence are considered to be of lower quality and are therefore less valuable than diamonds with a weak or no fluorescence. This is because strong fluorescence can detract from the diamond's natural brilliance and sparkle. 

However, this is a matter of personal preference, and some people prefer the look of diamonds with fluorescence.  There are even some studies which documented that low levels of fluorescence can result into an improved the appearance of certain diamonds with lower colour grades under direct sunlight.

Fluorescence

The length-to-width ratio of a diamond refers to the ratio between the length of the diamond and its width, which are two of the key proportions that affect a diamond's appearance and overall value. The length-to-width ratio is expressed as a decimal or fraction and provides a way to compare the shape of different diamonds.  

The length-to-width ratio affects the appearance of the diamond by determining the shape and outline of the diamond. Different length-to-width ratios will result in different shapes, with some shapes appearing more elongated and others appearing more squat. The ideal length-to-width ratio will depend on personal preference and the specific needs of the diamond and setting.  For example, a length-to-width ratio of 1.00 (or 1:1) would result in a perfectly square (or round) diamond, while a length-to-width ratio of 1.50 (or 3:2) would result in a diamond that is slightly elongated in the direction of the length. 

Some popular shapes, such as the round brilliant and princess cut, have established ideal length-to-width ratios that are widely accepted in the industry, but the ideal length-to-width ratio will depend on personal preference.  When selecting a diamond, it's important to consider the length-to-width ratio along with other factors, such as the cut, carat weight, clarity, and color, to achieve the best overall appearance and value for the diamond.

Length / width ratio

The diamond depth in millimeters is a measurement of the height of a diamond from the culet (the bottom point) to the table (the flat surface on the top). It is expressed in millimeters and gives a more precise measurement of the diamond's height than the diamond depth percentage.  

The diamond depth in millimeters can be calculated using the diamond's diameter and the diamond depth percentage. To calculate the diamond depth in millimeters, multiply the diamond's diameter by the diamond depth percentage, expressed as a decimal. For example, if a diamond has a diameter of 7 mm and a depth percentage of 60%, the diamond depth in millimeters would be 4.2 mm (7 x 0.6).  

It's important to keep in mind that the ideal diamond depth in millimeters can vary depending on the shape of the diamond and personal preference, just like the diamond depth percentage. A well-proportioned diamond will have a depth that balances with the other factors, such as the cut, carat weight, clarity, and color, to achieve the best overall appearance and value for the diamond.

Depth

The diamond depth percentage is a measurement of the height of a diamond from the culet (the bottom point) to the table (the flat surface on the top) as a percentage of the diamond's total diameter (the girdle, which is the widest part of the diamond). 

A well-proportioned diamond typically has a depth percentage between 59% and 62%.  For example, if a diamond has a diameter of 7 mm, and the distance from the table to the culet is 4.2 mm, the depth percentage would be 60% (4.2 ÷ 7 x 100).  It's important to note that while a diamond with a depth percentage in the range of 59-62% is considered well-proportioned, the ideal depth percentage can vary depending on the shape of the diamond and personal preference. 

Some diamond shapes, such as emerald and pear cuts, may look better with a slightly shallower depth, while others, such as round and cushion cuts, may look better with a slightly deeper depth. Ultimately, the depth percentage should be balanced with the other factors, such as the cut, carat weight, clarity, and color, to achieve the best overall appearance and value for the diamond.

Depth percentage

The diamond table % refers to the size of the flat facet on the top of a diamond, expressed as a percentage of the diameter of the diamond. The table is one of the key components of a diamond's cut, and can greatly impact the diamond's brilliance and fire.  

To calculate the diamond table %, you divide the width of the table facet by the diameter of the diamond and multiply by 100. For example, if the width of the table is 4mm and the diameter of the diamond is 8mm, then the table % would be 50%.  The size of the diamond table % is an important factor to consider when evaluating a diamond's cut quality. In general, a table % that is too large or too small can negatively impact the diamond's light performance and overall appearance. 

For round brilliant cut diamonds, the ideal table % typically falls within the range of 53% to 64%, with the optimal range varying depending on the diamond's other proportions and cut quality. However, it's important to note that the ideal table % can vary depending on the shape of the diamond and the individual preferences of the buyer.

Table percentage

A hearts and arrows pattern is a specific type of optical symmetry that can be observed in a round brilliant cut diamond. When viewed under a special scope, a diamond with excellent symmetry and proportions will display a pattern of eight hearts when viewed from the bottom and eight arrows when viewed from the top. 

The hearts and arrows pattern is a relatively recent development in the history of diamond cutting. It first emerged in the 1980s as a result of advances in technology and the growing demand for diamonds with superior optical performance.  The concept of the hearts and arrows pattern was pioneered by a group of Japanese diamond cutters who were seeking to create diamonds with maximum light performance. They used computerized imaging and analysis to study the precise angles and proportions needed to achieve the ideal pattern.  The Japanese cutters soon began marketing their hearts and arrows diamonds as a premium product, and the trend quickly caught on in other parts of the world. 

Today, hearts and arrows diamonds are recognized as a hallmark of excellence in the diamond industry, and they are highly sought after by discerning buyers.  The hearts and arrows pattern is created by the interaction of light with the diamond's facets. When light enters the diamond, it reflects off the facets and travels back to the observer's eye. In a diamond with excellent symmetry and proportions, the light is reflected back in a precise and uniform manner, resulting in the formation of the distinctive hearts and arrows pattern. 

Diamonds with a hearts and arrows pattern are highly sought after because they are considered to be of exceptional quality and beauty. The pattern is an indication of the diamond's superior cut and symmetry, which can enhance the stone's brilliance, fire, and scintillation. Hearts and arrows diamonds are often evaluated based on the quality and consistency of their optical symmetry. 

There is no standardized grading system for hearts and arrows diamonds, but the following are some of the commonly used terms to describe the different levels of hearts and arrows patterning:  
1. Excellent: This is the highest grade of hearts and arrows diamonds, indicating that the diamond exhibits a perfect pattern of eight hearts and eight arrows, with very high consistency in shape and size, as well as sharpness and symmetry of the facets.  
2. Very Good: This grade indicates that the diamond has a mostly uniform pattern of hearts and arrows, with some slight variations in shape and size of the facets.
3. Good: This grade indicates that the diamond has a discernible pattern of hearts and arrows, but with some visible irregularities in the symmetry of the pattern. 
4. Fair: This grade indicates that the diamond has a weak or partial pattern of hearts and arrows, with significant irregularities in the shape and size of the facets.
5. Poor: This grade indicates that the diamond has little or no discernible pattern of hearts and arrows, and its optical symmetry is significantly below average.  


It's worth noting that the hearts and arrows pattern is just one aspect of diamond quality, and it's important to consider other factors such as the diamond's color, clarity, and carat weight, as well as the overall cut quality, when choosing a diamond.

Hearts & Arrows

The girdle thickness of a diamond refers to the width of the diamond's girdle, which is the widest part of the diamond located at the circumference and separating the crown (the top portion of the diamond) from the pavilion (the bottom portion of the diamond). 

The girdle thickness is typically expressed in terms of "thick," "medium," "thin," or "extremely thin."  In general, a girdle percentage of 2-6% is considered a medium girdle thickness, which is the best balance between appearance and protection. 

However, the ideal girdle percentage will depend on the specific needs of the diamond and setting, and it's important to consider the girdle thickness in conjunction with other factors, such as the cut, carat weight, clarity, and color, to achieve the best overall appearance and value for the diamond. The ideal girdle percentage can vary depending on the diamond's cut and shape, as well as the type of setting it will be in. A thicker girdle provides extra protection to the diamond and can help prevent chips and cracks, but it can also affect the overall appearance of the diamond by making it appear smaller. A thinner girdle can make the diamond appear larger, but it can also increase the risk of damage.

Girdle

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