Diamond grading is a complex process done by gemologists who are professionals that identify, assess and value gemstones. The quality of a cut gemstone is determined by a number of factors, not all of which are visible to the naked eye. Each of these parameters must be carefully and separately assessed by an expert in order to determine the overall value of a diamond.
There is a globally recognized standard known as the 4Cs which is used to assess the quality of diamonds. The 4Cs have arranged the assessment of diamonds into a system and they have also unified it across the world's laboratories. The 4Cs are split into the following categories:
Color
It may be somewhat surprising to learn that color is one of the four main assessment criteria for colorless diamonds. It would therefore be more accurate to say that what is actually assessed is how close the stone is to being colorless. A completely colorless diamond is very rare. In fact, natural diamonds contain added chemicals of other elements and when it comes to clear diamonds, this is nitrogen, which colors the stone from yellow to yellow-brown in varying degrees.
When it comes to classifying the color of clear diamonds, a system of comparison is used. This is most often done on the internationally accepted GIA Color Scale (the scale was compiled by the GIA but the added verbal descriptions have been adopted by the HRD laboratory which bases its scale on the GIA one). The GIA scale works with the letters D-Z, which are used to denote the individual quality levels as follows:
- D to F – colorless diamonds;
- G to J – near colorless diamonds;
- K to M – faint. Diamonds with a hint of coloration;
- N to Z – diamonds with a yellow-brown tinge.
A perfectly colorless diamond is graded D. Each successive grade after that has a tinge of yellow in rising degrees of intensity but this color may not be noticeable to the untrained eye at all. The coloration is often only noticed when the diamond is compared to a colorless diamond graded D. And this is exactly how a diamond is assessed in a laboratory, resulting in a precise color grade.
Determining the color grade of a white diamond is done visually using a comparative set of diamonds called master stones. These could be real diamonds that meet the quality requirements (VS clarity and a weight of at least 0.7 ct) or imitations. In addition, electronic colorimeters or other system of comparison are used to determine the grade precisely. These are mainly used for gemstones already set into jewelry, (since the color of the metal can distort the color of a clear stone), or for fancy (color) diamonds.
It’s important to remember that for white (colorless) diamonds, the yellow tinge in a diamond reduces its price. However, if you have a yellow diamond that is graded as a fancy diamond, then the color in it is desirable and its intensity can in fact increase its price.
The most commonly used diamonds in the jewelry industry are those with a color grading of between G - J. Diamonds assessed as I and J show very light traces of a faint yellowish color and therefore fall into the cheaper category of diamonds. This trace of color may not however be noticeable at all in the way the jewelry looks overall. In KLENOTA jewelry, we generally use diamonds with a G color grading.
Clarity
The clarity of diamonds is assessed under a loupe (a type of magnifying glass) at magnification of 10x. The process involves looking for and assessing various internal imperfections (crystals of other diamonds or minerals, cracks, feathers, clouds, bubbles, etc.) and how many there are in the stone. Any imperfections reduce the price of the stone and must be listed on the certificate where they are described as inclusions, including their location and dimensions. A flawless diamond shows no impurities even when magnified ten times.
Diamonds can be enhanced, most commonly with lasers. After treatment, they are classified in the appropriate clarity category and the certificate lists all the corrections that have been made. But having said that, it’s the small inclusions in a diamond that give it its natural character.
Diamonds are classified into several categories based on their clarity. The category names and labels as well as the number of categories may vary slightly depending on the laboratory where the certification of the diamonds is done. The scale has the following grades:
- LC/IF/F (Loupe Clean, Internally Flawless, Flawless) - the diamond does not contain any inclusions. Its clarity is also verified under a binocular microscope. These diamonds are investment grade diamonds. The LC designation is used by the HRD laboratory in Antwerp. Other laboratories refer to diamonds of the same quality as IF. The American GIA also has an additional higher grade of F. The difference between this grade and diamonds assessed as LC is very slight wear on the diamonds.
- VVS1 (Very Very Small Inclusions 1, Very Very Slightly Included 1) - a binocular loupe as well as a microscope is used to examine a diamond of this quality since the inclusion can be very difficult to spot even by a trained eye. Without a loupe it is not visible. These diamonds are very clear and are also used for investment purposes.
- VVS2 (Very Very Small Inclusions 2, Very Very Slightly Included 2) - the same applies as for diamonds graded VVS1 (they are also assessed under a microscope and are investment diamonds), but these diamonds have more inclusions or they are slightly larger.
- VS1 (Very Small Inclusions 1, Very Slightly Included 1) - at 10x magnification with a loupe, a trained professional will be able to see small inclusions but they would be difficult to spot without the magnification. An untrained eye wouldn’t be able to see anything. The inclusions tend to mostly be located in the peripheral parts of the diamond, where they are better hidden. These stones could be used for investment purposes, but diamonds of this quality are also commonly used in jewelry.
- VS2 (Very Small Inclusions 2, Very Slightly Included 2) - as with the VS1 grade, the inclusions can be identified under a magnifying glass, but the larger ones may also be located under the table of the diamond, which means that they are more visible. An untrained eye would not be able to notice them. These diamonds are used in more expensive jewelry.
- SI1 (Small Inclusions 1, Slightly Included 1) - small inclusions that are rarely visible to the naked eye. They are noticeable at 10x magnification with a loupe but they don’t reduce the optical properties of diamonds. These diamonds are commonly used in jewelry.
- SI2 (Small Inclusions 2/ Slightly Included 2) - small inclusions that are visible to the naked eye. Under a magnifying glass they are clearly visible. However, they don’t affect the optical properties of the diamond. These are the most commonly used stones in jewelry.
- I1 (Included 1) – there are numerous inclusions, clearly visible, but they don’t diminish the optical properties of the diamond. They are commonly used in the jewelry industry as a more affordable alternative to higher quality and more expensive stones.
- I2 (Included 2) – the inclusions are clearly visible to the naked eye and degrade the optical qualities of the cut stone.
- I3 (Included 3) - The worst quality grade a diamond can have. There are many very visible inclusions and the optical qualities of the stone are adversely affected by them. In addition, they can cause the diamond to crack when it is being set or during wear.
Carat weight
Carat weight is a physical measurement that expresses the weight of precious stones. It is abbreviated as the symbol ct and 1 carat exactly equals 0.2 grams. One gram is therefore equivalent to 5 ct. The karat (kt), which is used to express the purity of precious metals is a completely different measurement.
Precious stones are weighed to 3 decimal places and there are special scales which are used to weigh them. The weight can be rounded off, but special rules apply for this. The weight can only be rounded up if the number 9 is in the third decimal place. So a diamond weighing 0.999 ct can be rounded up to 1.0 ct. However, a 0.998 ct diamond will weigh 0.99 ct after rounding.
Because the parameters of a brilliant cut are so precise, we can estimate the approximate carat weight of a diamond in a brilliant cut just by knowing its diameter.
When choosing a diamond, it’s very important to remember that two 1ct diamonds are not worth the same as one 2ct diamond because the 1ct diamonds are not nearly as rare. A 2ct diamond will be much more expensive than both 1ct diamonds combined simply because of its rarity.
Cut
The cut is the most variable feature of gemstones. There are many ways a cut stone can look. When assessing this, the shape and type of cut are first described. Next, the quality of workmanship is examined and this is then broken down into three components - proportions, polish and symmetry.
All cuts have one thing in common: the desire to maximize the optical properties of the diamond. Each cut has precise parameters and percentages applied to the different parts so that light that enters the stone is maximized and reflected exactly where it should be. This is the only way the gemstone can shine. And it is exactly this which is examined when assessing the proportions of a stone. A stone that has been cut in the best way has a perfect balance of brilliance, fire and sparkle:
- Brilliance is the amount of white light that is reflected from a cut stone.
- Fire is the number of spectral colors that are produced when the white light coming from the cut stone is broken down.
- Sparkle refers to the degree of color play that is evident when the stone is moved from side to side.
In this respect, a perfectly done brilliant cut is an ideal that has not yet been surpassed. It has 57 facets (58 including the culet), precisely defined angles between the facets and an exact proportion in percentage terms to the crown and pavilion.
When checking the polish, the quality is particularly important. There must be no visible traces of stone cutting, that is, grooves, dull areas, dents, etc. All surfaces must be perfectly polished. The edges between the facets should be sharp and not show signs of wear, or of being under polished. The number of facets is also checked because it is possible that an extra facet may appear which has no place in a well-made cut.
The final factor is symmetry. The stone must have a symmetrical shape and a symmetrical cut. However, it is not only the whole that is considered, but also the symmetry of the individual facets. A perfectly cut stone may even exhibit what is known as the hearts and arrows effect.
If the cut lacks symmetry or the correct proportions have not been maintained, light escapes from the diamond and is reflected somewhere else other than where it should. In this case, black areas may be visible inside the diamond - it does not shine, it does not have any brilliance and its optical properties are simply not at the required level.
After all three sub-categories have been assessed, the cut of the diamond can be assessed as a whole. The assessment scale for this has five grades:
- I/E (Ideal/Excellent) - diamonds given this rating have been cut the best. They represent approximately 3% of the world's total production. They stick to all of the parameters and use light to the maximum. In terms of their cut, they are considered simply perfect. If their other Cs are also high quality, these diamonds would be suitable as investment diamonds.
- VG (Very Good) - diamonds with this grade comprise about 15% of the world’s production. Their optical properties are almost of the same quality as those graded I/E.
- G (Good) - about a quarter of the world's diamond production falls into this category. The optical properties are good and these diamonds reflect most light. They are ideal for jewelry but are not suitable for investment. To the untrained eye, they may be indistinguishable from higher grades.
- F (Fair) - these diamonds have less brilliance and the quality of their cut is lower. However, they are still considered high quality and are widely used in jewelry.
- P (Poor) - these diamonds are not well cut, light is lost in them and the stones have almost no brilliance. Reputable jewelers don’t use them in their jewelry.
The fifth C: Certification
While diamonds are graded according to the 4Cs, there is also another category called the fifth C. It doesn’t refer directly to the grading of the stone, but to its certification. Genuinely credible certificates which guarantee the quality and accuracy of the diamond's parameters as they are stated on the certificate are issued by specialist gemological laboratories. Among the best known are the GIA (Gemological Institute of America) and the IGI (International Gemological Institute). At the KLENOTA Jewelry Studio, we use this international certificate for jewelry with natural and laboratory diamonds weighing over 0.30 ct.
