The most important features of colourless diamonds evaluation - the 4C method

Each diamond is unique - but not all of them have the same value. Diamonds with a very good cut, impeccable clarity, great colour and considerable weight are among the rarest and their price is the highest. The most popular diamond grading system is the 4C method. 4C is an abbreviation derived from the first letters of the four English words cut, clarity, colour, carat. For some people in the diamond market, the cut in colourless diamonds seems to be the most important parameter. Another school talks about the same level of significance for each parameter. What is certain is that the cut is the most complex of all, and diamonds should be judged by all 4C parameters. Knowing this method will make it easier to navigate the diamond market.

Cut - the cut and polishing of a diamond

A very important parameter that is often confused with the shape of a diamond. The cut refers to the interaction of the diamond with the light falling on it. In a diamond that is cut perfectly, the light reflects and the stone shines. A diamond that has been cut too shallow or too deep - reflects poorly and presents itself poorly in general.

A perfectly cut diamond achieves various visual effects when exposed to light. A rough diamond does not possess these features.

A polished diamond under the influence of light and movement will achieve the following effects:

Brilliance - refers to the light that is reflected from the inside of the diamond. This is what makes the stone appear to glow. The rays of light fall inside the stone, refract and return, resulting in a sparkling diamond.

The brilliance can be compared to a window. Light enters through the window depending on how the glass absorbs it. The rays will pass through the window if the glass quality (diamond cut) is high. Uneven and defective glass will not transmit light rays as well as transparent glass. So is the diamond. The brilliance effect can be seen in the best cut diamonds. Those with a worse cut will not shine because they will not reflect light and will appear darker.

Dispersion (fire) - occurs when some rays of white light passing through a diamond are broken into the colours of the light spectrum. White light diffuses into all the colours of the rainbow.

Scintillation - refers to the colours that start to sparkle when the diamond is moved, for example, back and forth. In fact, as the stone moves, some facets should appear dark while others shimmer. 

Graph 1. Brilliance, fire and scintillation

Source: https://www.withclarity.com/education/user/pages/02.diamond-education/08.diamond-cut/14.diamond-brilliance/diamond-brilliance-fire-scintillation.gif 

Of all the features of the 4C group, the cut is the most complex and difficult to analyse parameter. Gemological Institute of America (GIA) divides diamonds, according to their cut, into 5 groups:

· Excellent - maximum brilliance and dispersion. It reflects almost all the light entering the diamond, creating a unique brilliance.

· Very Good - correctly reflects most of the light entering the diamond, creating excellent brilliance and dispersion. Under normal lighting conditions, it looks very similar to the Excellent Cut.

· Good - reflects most of the light entering the diamond resulting in an above-average look.

· Fair - allows much of the light entering the diamond to escape from the sides or bottom, reducing brilliance and dispersion.

· Poor - allows most of the light entering the diamond to escape from the sides or bottom. The diamond may appear noticeably dull.

 Chart 1. Reflection of the light inside the diamond

The cut is assessed on the basis of:

Symmetry. Assessment of the diamond cut in relation to the vertical axis (main axis of symmetry) and the horizontal axis (auxiliary axes). Symmetry affects the strength of a diamond's brilliance.

Polish. The quality of the polished surfaces of the diamond, which determines the external and internal reflection of the light. A diamond that is too poorly polished does not let light in and does not reflect it. It gives the impression of a stone "without life". A poorly polished diamond has micro pores on its surface that can absorb grease and other impurities, causing permanent damage to the stone.

Proportion. The ratio of the individual elements of the diamond structure to its diameter, expressed as a percentage. How well the light refracts inside the diamond depends on the proportions obtained. Depending on the shape of the diamond, its ideal proportions will be different.

Triple Excellent

A highly sought-after diamond whose cut, polarity and symmetry are of the highest GIA standard (Excellent). Not each such a diamond will immediately be more expensive, because other parameters such as colour, carat and clarity must also be taken into account.

Graph 2. Anatomy of a round brilliant cut

Glossary:

· Crown- the portion of the diamond’s anatomy above the girdle.

· Table - the biggest facet on the diamond, where light enters the diamond and the brilliance begins. 

· Star Facet - one of the eight small triangular facets adjacent to the table.

· Bazel Facet - one of the eight kite-shaped facets, connects the girdle to the table facet.  

· Upper Girdle Facet - the triangular facets which border on the top of the girdle.

· Girdle - the widest part of a diamond, its outermost edge (When looking at a diamond from the top, the girdle is the part of the stone that creates the outline).

· Pavilion - the base, the part of a cut gemstone below the girdle. 

· Lower Girdle Facet - the triangular facets which border on the bottom of the girdle.

· Pavilion Facet- one of the long facets which form the lower half of a diamond, below the girdle, which meet in a point at the culet. Pavilion facets reflect light back through the crown facets. 

· Culet - a flat face on the bottom of a gemstone.

There are also other shapes of cut diamonds. The most common and most valued is the brilliant cut (Tolkowski's round cut). It is called a perfect cut.

In the case of diamonds in fancy colours - the type of cut does not matter. Due to the fact that these are very rare stones, the shape is selected so that the mass of the polished diamond is as large as possible.

Graph 3. The proportions of a perfect diamond in a brilliant cut

Graph 4. Sample diamond shapes

Clarity 

Diamonds are formed deep under the Earth's crust under the influence of extreme heat and pressure. To a greater or lesser extent, practically all of these stones contain minor imperfections. When they occur inside, they are called inclusions. If they occur on the surface, they are called blemishes.

Clarity refers to the degree to which these imperfections occur. Diamonds that contain numerous or significant inclusions or blemishes have a lower brilliance because the blemishes interfere with the path of light transmission through the diamond.

The position of the inclusions affects how easily they can be seen. Diamonds are cut in such a way that the inclusions are not visible when viewed from above through the table (top of a diamond) of the cut diamond. Ideally, the inclusions should be under the facets (bazel) or near the girdle as they are more difficult to see.

A scale created by GIA and used worldwide to indicate diamond clarity:

· FL (Flawless) - no inclusions or blemishes under 10x magnification. The purity of FL is extremely rare, approximately 1 in 5,000 diamonds.

· IF (Internally Flawless) - no inclusions but blemishes under 10x magnification may be visible to an experienced diamond grader expert. As rare as FL. Diamonds with IF purity constitute less than 3%.

· VVS1 and VVS2 (Very, Very Slightly Included) - small inclusions, difficult to see even by a gifted expert under 10x magnification. Most often, inclusions in VVS1 are visible in the pavilion and in VVS2 in the diamond crown. VVS1 is a higher purity than VVS2.

· VS1 and VS2 (Very Slightly Included) - inclusions visible under 10x magnification but small in size. Not visible to “the naked eye”. Diamonds from this purity upwards are the most popular in jewelry. VS1 is a purity higher than VS2.

· SI1 and SI2 (Slightly Included) - minor Inclusions are visible under 10x magnification. SI1 is a purity higher than SI2. Inclusions in SI1 are often invisible to “the naked eye" and in SI2 they are often visible.

· I1, I2 and I3 (Included) - inclusions are visible under 10x magnification, as well as "with the naked eye". Can affect the brilliance of a diamond.

Graph 5. GIA clarity scale

Graph 6. Types of inclusions

Colour – colour of a diamond

The colour of a diamond is one of the most important parameters in the evaluation of colourless diamonds and undeniably the most important parameter in the evaluation of diamonds in fancy colours.

An international colour scale has been defined for colourless diamonds. It starts with the letter D, which denotes colourlessness. As the presence of colour increases, they are labelled sequentially up to the letter Z, denoting diamonds with an admixture of yellow or brown colour. 

Diamonds are colour-graded by comparing them with stones of known colour under controlled lighting and precise viewing conditions.

Graph 7. Colour scale of colourless diamonds

 Source: https://www.gemsociety.org/wp-content/uploads/2020/09/diamond-color-chart.jpg

The fewer colours in a colourless diamond, the higher its value.

The exception are diamonds in fancy colours - they go beyond the standard range of D-Z colours. These are very rare diamonds, which are a small fraction of the mined colourless diamonds. And it is the colour that proves their value - the more colour they have, the more valuable they are. We write more about these unique stones here (https://301carats.com/blogs/diamond-education-center/features-of-coloured-diamonds)

Carat - the mass of a diamond

Unlike a carat in gold, which determines the purity of an ore, a carat in diamonds determines the weight. It is approximately 0.2 gram.

NB. Larger stones of a certain weight (e.g. 2 ct) are worth more than several smaller stones of the same total weight (e.g. 0.5 + 0.7 + 0.8 ct).

Graph 8. Carat scale

The 4C grading method is the starting point for diamond grading

Each diamond can be evaluated using the parameters of the 4C method. Undoubtedly, it has many advantages, because all cut stones can be assessed using the same guidelines. Unfortunately, the method is not perfect. Each stone is different and requires an individual approach. Its benefit or disadvantage may be influenced by other parameters not classified in the 4C method, e.g. fluorescence. That is why an individual approach to each of them is so important in assessing colourless and coloured diamonds. The 4C method is a great start - but it will not allow you to fully evaluate a diamond.

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