Useful information about diamonds and how they are graded
The Four C's
Gemmologists and jewellers assess how of diamonds using the 4Cs classification system – cut, carat, colour and clarity.
The 4Cs classification enables the comparison and valuation of diamonds. No one 'C' is more significant than another, and none will diminish in value over time.
A rough diamond prior to cleavage and polishing
The general structure of a round polished faceted diamond
To cut a diamond perfectly, a craftsman will often need to cut away more than 50% of the rough diamond.
A well-cut diamond will internally reflect light from one mirror-like facet to another and disperse and reflect it through the top of the gem. The facets, when arranged in precise proportions, will maximize the fire life and brilliance of a diamond.
A well-cut diamond will be higher in quality and value than deep or shallow-cut diamonds. Diamonds that are cut too deep or too shallow lose or leak light through the side or bottom, resulting in less brilliance and a less valuable stone.
Different Diamond Shapes
Round diamonds are symmetrical and capable of reflecting nearly all the light that enters, so it is the most brilliant of all diamond shapes and follows specific proportional guidelines.
Non-round shapes, also known as ‘Fancy shapes’ have guidelines in order that they are considered to be well-cut. EMIGEM.COM sells the following diamonds shapes; however shapes such as Radiant, Asscher, Oval, Marquise, Heart, Pear and Cushion are more scarce in comparison to Round, Princess and Emerald.
Measurements, Proportions and Diamond Cut Grade
The proportions of a diamond are measured in millimetres. According to each shape, the measurements of a diamond are determined by the size of the diamond, the shape of rough being polished, the stones proportions after polishing and the symmetrical alignment of the facets. The diamond's proportions include an assessment of the crown and pavilion angles, facet lengths, girdle thickness and culet size. Measurements are also useful for identification purposes. A well proportioned diamond will result in more brilliance. I.e. The depth to width ratio of a diamond is important, as it influences the amount of light being reflected from of the face of the diamond I.e. How much life or brilliance the stone has.
There are different opinions on the ideal proportions of a round diamond, however Marcel Tolkowsky outline the proportions of an ideal cut diamond in 1919 in his book Diamond Designs. Since then there have been numerous variations and improvements to increase the brilliance of a diamond by tweaking proportions and changing the Facet arrangement of the stone. Many working in the diamond industry prefer different proportions that don’t reduce the size and look of the stone. A good cut that maximises look and size, is known as one that follows the 60/60 rule; the size of the table and depth should reach 60% of the diameter of the stone. The struggle of all diamond polishers is obtain the maximum amount of diamond weight and still maintain ideal proportions for the maximum return of light. The grades given to the ‘Cut’ of a diamond may differ amongst independent laboratories.
A desirable Fancy shape can be subjective in nature, as not everyone agrees on the ideal proportions of the length-to-width ratio of the stone.
One can understand the ratio by taking the length of the diamond and dividing it by its width. This ratio will differ for each shape and according to a person’s taste.
Due to the subjective nature of the ideal Fancy shape, until now ‘The Cut Grade’ is only given to Round Diamonds and by few laboratories such as GIA and AGS. It is determined by a combination of factors, including Proportion, Polish, Girdle thickness, Symmetry and Culet size and is graded as Excellent (Ideal) , Very Good, Good, Fair or Poor or alternative grading systems depending on the laboratory.
Polish refers to the smoothness of the facets after polishing. Grain lines may appear on the surface of stones facets as a result of poor polishing. These lines are usually microscopic and run across the Facet. This can affect the lustre of a diamond, reducing the intensity of light reflected from the diamond. This affects the value of a diamond. The actual Polish grade will depend on the laboratory examining the stone and may include the grades Excellent, Very Good, Good, Fair and Poor.
Symmetry is graded with same system as polish but refers to the placing and alignment of the facets. Facets should align perfectly. If not it can result in poor reflection of light, an uneven shape to the stone and even affect the setting of the diamond in jewelry. Diamond polishers may allow for imperfect symmetry to maximise the weight of the diamond and therefore increase its value. There is often an intentional compromise between the weight and beauty of the stone to achieve optimum value.
Carat is the measure of the weight of a diamond, abbreviated as ‘CT’. There are one hundred points to a Carat. E.g. A ‘25 Point diamond’ is equal to ¼ CT or 0.25CT. In the diamond industry1/4CT is also referred to as a ‘Grain’. So a ‘3 Grainer diamond’ weighs 3/4CT.
The word carat derives from the Greek word 'Keration' meaning fruit of the carob. The Carob tree (Ceratonia siliqua) is an evergreen tree, with an edible pod containing seeds, which is native to the Mediterranean region. Historically the seeds of the Carob were used on precision scales as units of weight for small quantities of precious gemstones because of their uniform size. The weight of an average carob seed is 200 milligrams. The weight of one carat is precisely 200 milligrams, or 0.2 grams.
The Carat weights influence on value
In truth the Carat refers to the weight of the diamond as opposed to the size. However in a well proportioned diamond, weight will be and indicator of size and vice-versa. E.g. a well proportioned round 1.00CT diamond should have a diameter of between 6.3-6.5mm.
Usually the larger the diamond the more the value increases, as larger stones become scarcer. There is a disproportionate increase in the value of a diamond the heavier the stone gets; consequently disproportionate jumps in prices as the diamond weight goes over threshold weights e.g. 0.50CT, 0.75CT, 1.00CT etc.
As discussed previously there is a trade-off between the proportions of a stone and its weight. The polisher wishes to maintain the weight of the stone because of the disproportional increase in value, but may need to compromise the stones beauty and ability to reflect light. This may mean for example maintaining weight by keeping the Girdle (the belt around the middle of the diamond) thicker than necessary or affecting the polish or symmetry of the stone.
Most natural diamonds contain small quantities of nitrogen atoms evenly dispersed throughout the stone, absorbing some of the blue spectrum, thereby making the diamond appear yellow. The higher the amount of nitrogen atoms, the yellower the stone will appear.
GIA (The Gemological Institute of America) uses the scale of ‘D’ to ‘Z’ to grade the color of diamonds, where ‘D’ is completely colorless and ‘Z’ is yellow. Other laboratories HRD, IGI, AGS, and EGL use similar grading systems. For this explanation on color we will use GIA’s grading system as it is a bench-mark for the industry. EMIGEM.COM sells certified diamonds from D to M color I.e. Colorless to Faint Yellow.
The effect of Fluorescence is noticeable in some diamonds when exposing a diamond to a ultra-violet light, usually projecting a blue glow; the stronger the fluorescence the stronger the glow. In stones with a yellow color, this may improve the color making the stone more colorless. In some cases the stone may appear mistier to the trained eye, then a stone with no fluorescence. A customer may benefit by purchasing a diamond with an improved color (in appearance) at a slightly discounted price, therefore offering better value.
“Diamonds have internal features, called inclusions, and surface irregularities, called blemishes. Together, they're called clarity characteristics. A clarity grade is determined by the relative absence of clarity characteristics.
International Grading Laboratories and Certification
EMIGEM.COM offers diamonds which have been graded and certified by five different international laboratories GIA, HRD, IGI, AGS and EGL. Below are excerpts from each diamond grading organization’s web-site promoting and explaining a little of history and mission. However the bottom line is that the value of the certificate is reflected in the price being asked for the stone. Two diamonds holding the same certificate parameters can have startlingly different prices. EMIGEM.COM leaves it to the customer to decide which certificate report provides them with the best value for their money. As always the market decides. If you want further advice regarding the quality of diamond certificates and their grades, please contact EMIGEM.COM Customer Service.
Most laboratories offer several types of certificates. EMIGEM.COM Diamonds offers Full Certificates for Diamonds over 1.00CT and Smaller (Dossier) Certificates for Diamonds below 1.00CT. Accompanying most of the diamonds listed on the EMIGEM.COM web-site, will be a link to the picture of the certificate it holds. In any case the majority of each diamonds parameters are listed in the Diamond profile page, in detail. In full certificates, the certificate may contain a diagram plotting inclusions and blemishes on the stone. Certificates will be shipped with the diamond, when ordering.
“Established in 1931, GIA is the world’s largest and most respected non-profit institute of gemological research and learning. Conceived 75 years ago in the grand tradition of Europe’s most respected institutes, GIA discovers (through GIA Research), imparts (through GIA Education), and applies (through the GIA Laboratory and GIA Instruments) gemological knowledge to ensure the public trust in gems and jewelry. With 1,100 employees, the Institute’s scientists, diamond graders, and educatorsare regarded, collectively, as the world's foremost authority in gemology”
Hoge Raad voor Diamant (HRD)
With this renewed identity the umbrella organization wants to address the continuing growth and the increasingly faster internationalization of the sector. Therefore, the Diamond High Council opted for ‘HRD’, a single universal brand, recognizable all over the world and synonymous with a unique service. At the same time, the baseline ‘Antwerp World Diamond Center’ has been integrated in the logo. Needless to say, the new logo has to illustrate that HRD has become one of the world’s most respected institutes serving the international diamond scene.”
International Gemological Institute IGI
“Established in Antwerp, New York, Hong Kong, Mumbai, Bangkok, Tokyo, Dubai, Toronto, Los Angeles, Tel Aviv and Cavalese, IGI is the world's largest independent gem certification and appraisal institute and is renowned for its quality services, extensive experience and know-how.
IGI, the oldest institute of its kind in Antwerp, was founded in 1975 and along with its sister laboratories is one of the leading gemological institutions worldwide.
Presently, a staff of just three has grown to over 450 professionals dedicated to a standard of excellence second to none and IGI issues more than one million reports per year.”
American Gem Society (AGS)
“The AGS Laboratories is the world’s premier diamond grading laboratory for diamond cut, the premier laboratory to offer a diamond cut grade for fancy shapes such as princess cut and emerald cut, and the foremost diamond grading laboratory created to protect the consumer. AGS Laboratories diamond grading reports offer an easy-to-read grading scale that provides a simple basis for comparison to other diamond reports. The AGS Laboratories Diamond Reports provide you with all the information you need to make the best possible buying decision.
“EGL USA is one of the largest and oldest independent gemological institutions focusing on gemstone certification and research. Originally part of an international network founded in Europe in 1974, EGL USA opened its first U.S. lab in the heart of New York's international diamond and jewelry district in 1977.
In 1986 EGL USA became independently owned. Today the EGL USA Group has laboratories in New York City, Los Angeles, Vancouver, and Toronto.
EGL USA is not affiliated with any other EGL labs outside North America.
Every certificate issued by our lab states "A member of the EGL USA Group." Certificate numbers are preceded by either "US" or "CA," to indicate country of origin and to provide consumers the assurance that their certificate has been issued by a member of the EGL USA Group.”
European Gemological Laboratory (EGL)
“The president of E.G.L. Mr. Guy Margel completed his gemological training in the United States in the late 1960's. In 1973 Mr. Margel opened the first European Gemological Laboratory in Antwerp. The services offered by the E.G.L. laboratories are recognized throughout the world and the company is an integral part of the global diamond industry.
To take the guesswork out of buying diamonds by providing diamond grading consultations and certificates to internationally accepted standards. Our customers are professional diamond wholesalers, retailers, manufactures and craftsmen in the diamond industry. We do not sell diamonds and we are totally independent of any diamond sales organisation.
To provide professional diamond grading education for those interested in diamonds and comprehensive courses in coloured stones for those who wish to enter the industry and for those persons already in the industry who wish to enhance their knowledge.
Grading diamonds is not an exact science, rather an applied science or discipline based on training, competence and the experience of thegemologists. To maintain our reputation for accuracy and consistency we have defined criteria and standard procedures which are adhered to by the EGL laboratories. With our qualified staff and 27 years of experience we are in the position to provide you with fast and efficient services.”