The table below details the various laboratories and the different grading scales they use, you will notice that there is an over lap in some of the grades and that the top grade is not the same for each laboratory.
GIA and DCLA have Excellent as their top grade, HRD has Very Good for its top grade whilst AGS splits its top grade category into Ideal and Excellent.
DCLA & GIA have the same grade categories except DCLA calls its second lowest grade Medium whereas GIA calls it Fair. AGS has the same breakdown of catgeories as both DCLA & GIA except for the top grade of Excellent where it breaks down that category into two sections of Ideal - AGS0 and Excellent - AGS1.
AGS is the only Grading Laboraotory that actually has a grade called Ideal. The term Ideal Cut Diamond is a widely and quite oftenly misused marketing term used by Jewellers and Diamond Dealers to describe a cutting style based on proportions rather than an actual Ideal grade by a laboratory unless the diamond has been certified by AGS with and AGS grade of Ideal - AGS0
The cut of a diamond refers to its proportions, symmetry and polish. These are the three main factors that affect the diamond's ability to return light. Another term that is used to describe a diamond's light performance is "brilliance".
A diamond that is ideally cut produces high light return, scintillation, fire and spectacular brilliance. A poorly cut diamond causes light to leak out the bottom or sides of the diamond, thereby minimizing the amount of light that is allowed to reutrn via the diamond's top and specifically its table. Even a diamond that has exceptional color and clarity can appear lifeless and dull when it is poorly cut. For this reason, The Diamond Vault suggests that you choose the diamond with the highest cut grade that falls within your budget.
A diamond cut by shape describes the outline of the stone and pattern of the facet arrangement. A stone can be cut in various shapes like Round, Princess, Emerald, Oval, Marquise, Pear, Asscher, Radiant Heart, Cushion, Baguette, Trillion etc. We will further explore various diamond Shapes in the Shape section.
The GIA (Gemological Institute of America) colour grading classification starts from D, the finest colour grade (colourless), and continues through the alphabet to Z becoming progressively more tinted to yellow. A set of master comparison stones calibrated to the exact colour of every colour grade is the most reliable method of grading diamonds for colour. This allows for the accurate colour grading of the diamond.
Diamonds come in a variety of colors, some of them highly prized (pinks, blues, even yellow). However in a white diamond, the presence of a yellow tint will lower the price of a diamond. The less body color in a white diamond, the more true color it will reflect, and thus the greater its value.
Every Diamond has been assigned a color grade by the GIA ( Gemological Institute of America) in a viewing environment specially designed to eliminate color from surrounding surfaces as well as the light source itself. This allows the color of the diamond to be accurately measured. Minor differences in diamond color detected in this environment are very difficult if not impossible to detect in a normal environment. The diamond industry has adopted the GIA (Gemological Institute of America) diamond color scale; almost every diamond sold today is rated using the GIA color scale, whether it was actually certified by the GIA (Gemological Institute of America) or not.
The GIA (Gemological Institute of America) grades diamonds on a scale of D (colorless) through Z (light color). All D-Z diamonds are considered white, even though they contain varying degrees of color. True fancy colored diamonds (such as yellows, pinks, and blues) are graded on a separate color scale.
Below is the GIA (Gemological Institute of America) diamond color chart with definitions, accompanied by further explanatory comments from Diamond Bourse.
A diamond that is absolutely colorless is incredibly rare. In fact, even the most expensive Diamonds used in Jewelry are typically not completely colorless. Diamond color grades start at the letter D, or absolutely colorless, and go all the way to the letter Z. Colorless Diamonds range from D to F. To the eye of an experienced jeweler, even one using magnification, a colorless diamond will have no visible coloring. The only colors you might see are the ones that are reflected through the light in the diamond's various facets. A colorless diamond is top of the line, although they are hard to find and afford because of their rarity.
Some Diamonds are virtually colorless, but close inspection reveals very subtle hints of yellow. In G or H near colorless Diamonds, these hints of yellow might only be visible under 10x magnification. Often, the only way to even pick up on these minor color issues is to compare a new colorless diamond to a D colorless diamond. Side by side, it might be easier to spot any imperfections in the color of the diamond. Near colorless Diamonds classed as I or J may have some yellow undertones that are visible to the unaided eye. Often, near colorless Diamonds are a great choice to pair with white or yellow gold.
The next category of diamond color grades is faint yellow. Even to the untrained eye, these Diamonds are not colorless. Although the classification is yellow, it's important to note that these Diamonds might also appear slightly brown or even grey. While they aren't colorless, they can still be beautiful. These are typically a more affordable choice for buyers, often coming it at half the price of a E or F diamond. They look best in a warm setting like yellow gold. The clearest of the faint yellow Diamonds is classed as a K, followed by L and then M, which is the most yellow in this category.
Very light yellow Diamonds are the next category of diamond color grades. Right away, looking at a very light yellow diamond will reveal that it is not colorless. Compared to a truly colorless diamond, a very light yellow diamond might look yellow, grey or brown. While these Diamonds are readily available, they are less common for engagement rings or high-end pieces. Nonetheless, they are typically an exceptional value because of reduced demand for this color. The subcategories of very light yellow Diamonds range from N to R, with N being the lighter in color and R being the darkest.
Technically, these Diamonds are still classified as white Diamonds. This makes them different from fancy color Diamonds, which might be a distinct color. However, light yellow Diamonds are obviously not colorless in any way. They are visibly a different color, and many people find the hues of these affordable Diamonds to be unappealing. In the right setting, perhaps with a yellow gold cup under the stone, a light yellow diamond can be colorful and eye-catching. You might have a hard time finding light yellow Diamonds in a Jewelry store simply because there is very limited demand for them. Light yellow Diamonds can be classified from S all the way to Z, with Z Diamonds being the darkest in color.
Although majority of diamonds come in shades of white, there are also "Fancy" natural intensely colored diamonds available in colors like yellow, pink, greens, brown, red, orange, blue etc. These intensely colored diamonds are very rare, attractive and desirable. A deeply colored diamond can cost more than its colorless counterpart. These intensely colored diamonds are known as "Fancy" colored or "Fancies". Fancy colored diamonds are graded in two ways. The first factor is the basic hue, such as pink, yellow, blue, green, etc. The second is the intensity. Both color characteristics form the basis for determining a fancy colored diamond's worth. In fancy colored diamonds, a Z+ grade is used for their color grading. Usually, the more intense the color, the rare and expensive the diamond will be. For example, a fancy light pink diamond costs less than a fancy vivid pink diamond of equal size, shape and clarity. Though fancy colored diamonds rarely occur in nature, laboratories can easily create them through irradiation and heating. This process can permanently turn a natural colorless diamond into a fancy colored diamond. Treatments have also been developed to make lower-color white diamonds whiter. Irradiated colored diamonds have a significantly lower value than natural fancy diamonds and can be detected in a gem laboratory.
Clarity is a term used to describe the absence or presence of flaws inside or on the surface of a diamond. In other words, the clarity of a diamond refers to a diamond's clearness or purity.
When these flaws / marks occur internally, they are called inclusions. The most common types of inclusions include crystals, (tiny bubbles representing small minerals that were absorbed into the diamond while it was growing), internal graining, needles, knots, chips, cavities, cleavage, feathers, and clouds. On the contrary, when these flaws / marks occur on the surface, they are known as blemishes. The most common types of blemishes include polish lines, naturals, scratches, nicks, pits, transparent stress lines that appear on a diamond's surface, surface graining, and extra facets. Blemishes are usually cut to remove a near-surface inclusion to raise the clarity grade of a stone. Most diamonds have these imperfections in them. Although many of these flaws are not visible to the naked eye, but under magnification, tiny featherlike shapes, crystals, bubbles and dark flecks become noticeable. These slight flaws make every diamond quite unique but they also affect the beauty and value of the diamond.
A diamond's clarity is based on the number, size, nature, and location of imperfections on the finished stone. A diamond with higher clarity is more valuable in comparison to a diamond that contains numerous inclusions because it is less brilliant, as the inclusions interfere with light passing through it.
Because they are formed deep within the earth, under extreme heat and pressure; virtually all diamonds contain "birthmarks"; small imperfections inside the diamond (called inclusions), or on its surface (called blemishes). Clarity refers to the degree to which these imperfections are present. Diamonds which contain numerous or significant inclusions or blemishes have less brilliance because the flaws interfere with the path of light through the diamond.
The position of an inclusion affects how easily it can be seen. Diamond cutters make every effort to cut a stone so that inclusions are not visible through the table of the finished diamond. The preferred position for inclusions is under the bezel facets or near the girdle because they are harder to see there.
Almost all diamonds are graded for clarity using the 11 point diamond clarity scale created by the GIA, including diamonds which were not actually graded by GIA certified. In grading diamond clarity, the GIA considers the number, size, color, reflectivity, and position of every flaw visible under 10x magnification.
Carat is the measure of how much a diamond weighs. Diamond carats is often denoted as “carats” or “ct.”.
A carat is a type of weight measure. Diamonds, just like other kinds of gemstones, are weighed using the metric carats.
A carat equals two-tenths of a gram or 200 milligrams, (1 carat = 0.2 grams = 200 milligrams).
Each carat is then divided up into 100 total points. (1 carat = 100 points)
Therefore, a 50-point gemstone can be expected to weigh 0.50 carats or 1/2 of a carat.
The origins of using the carat as a measurement of weight come from the early days of trading when carob seeds were used as counterweights to balance scales for gem traders. These seeds were generally a uniform weight, so their use was something everyone could agree on as a way of measuring weight. Over time, this evolved into the carat weights used today.
The abbreviation of "CT" is used specifically for carat, which refers to the weight of one diamond or gemstone. Example 1 carat will be denoted as 1 CT.
There are carat abbreviations that are single, and abbreviations that are used for total weight, some of them are explained below.
The price of a diamond is calculated by multiplying the diamond carat weight by per carat price. Example if a diamond weighs 0.50 carats and the market price per carat is $2000/carat. Then the 0.50ct diamond will cost you $1000.
Total Carat Weight * Price Per Carat = Diamond Price
0.50ct * $2000 = $1000
Similary, if a diamond weighs 1.50 carats and the market price per carat is $4000/carat. Then the 1.50ct diamond will cost you $6000.
1.50ct * $4000 = $6000
The price per carat varies based on the Diamonds characteristics. The base price per carat is determined using a combination of carat weight, clarity, and color. Other characteristics of the diamond such as cut, fluorescence, polish, etc. can add a premium or discount the base per carat price. The per carat price is dynamic and changes weekly varying based on the demand and supply of Diamonds available globally.
The price per carat is not a linear measure and multiplies exponentially. This is mostly because larger Diamonds are rarer than small ones. So a larger diamond does not only cost more. Its also costs more per carat.
Carat is not to be confused with Karat. Carat, as explained above, is a weight unit of measure for Diamonds and gemstones, while karat is the measure of purity for the precious metal gold. Both of them are pronounced very similarly so one has to be careful when having a verbal discussion to be aware and know the difference. Carat is denoted as (ct) and Metal Karat is denoted as (k). Carat is also not to be confused with a carrot :