Diamonds are graded according to the 4C system, i.e. cut, colour, clarity and carat weight.

So what is the 4C system?

The "4Cs" is a global standard for the four main characteristics of diamonds: cut, colour, clarity and carat weight. These qualities interact with each other to create the beauty and sparkle that make diamonds so appealing.

If you are planning to buy a diamond, it is important to have a basic understanding of what these terms mean and why these ratings are important. However, if you plan to buy based on this knowledge alone, beware. Jewellers often try to push substandard diamonds on gullible customers. Therefore, while an understanding of the 4Cs is a very important starting point, these ratings alone are not sufficient to make a purchasing decision. Work with an expert you trust, and you are sure to get a better diamond and a better price.

Below is a brief description of all four characteristics.

Cutting and polishing

Cutting is essential to the beauty of a diamond and is not an area to skimp on. The GIA (Gemological Institute of America) grading is a good guide to cutting round brilliant diamonds, but there are no guidelines for cutting other diamond shapes. For non-round diamonds, it is essential to work with an expert to review high-quality diamond images.

The cut grade of a diamond shows how all the dimensions of the stone interact with each other to create a visual effect. The faceting of a diamond determines how much light the stone will reflect. A poorly cut stone will appear lifeless - dark or transparent like glass. A well-cut diamond has a huge impact on appearance, which is why this characteristic is usually referred to as the most important of the 4Cs.

The GIA has a comprehensive set of standards for the analysis of round brilliant cut diamonds, which it has developed to maximise the desired visual effects:

Radiance: the inner and outer white light reflected off the diamond

Dispersion: dispersion of white light into all colours of the rainbow

Scintillation-glow: the sparkle-glow of the diamond and the pattern of light and dark areas resulting from reflections within the diamond.

Cutting is divided into 3 parameters: proportion, symmetry and cut. Each criterion is evaluated separately according to the following quality classes:

Ideal faceting. Such diamonds reflect light to the maximum. Among diamonds for sale, approximately 3% are perfectly faceted.

Very good faceting. Gemstones with this cut reflect almost as much light as those with an ideal cut. The number of such diamonds is around 15%.

Good faceting. These diamonds reflect less light than they receive. There are approximately 15% of such stones in the range.

Medium faceting. Such diamonds are still considered to be of high quality. Medium-cut diamonds account for around 35% of all diamonds sold.

Poor faceting. Such diamonds reflect light poorly and do not shine.

A diamond with an ideal shape reflects most of the light through the top facet. If the diamond is cut too flat, some light will be lost through the bottom cut. If the diamond is too elongated, light will be lost through the edges. 

Colour

A diamond's colour rating refers to the level of colourlessness of the diamond, particularly its yellow hue. Slight variations in ratings are slight and may be outweighed by other factors such as the shape of the diamond and the metal in which it is set. 

Few diamonds are naturally colourless. Most are yellowish (but brown, grey or greenish), due to traces of nitrogen. It is the colourless diamonds that are the most prized. The GIA has developed a standard colour scale for diamonds, ranging from D (colourless) to Z (light yellow). This scale is divided into 5 categories.

Colourless. This category includes diamonds marked with the letters D, E or F. Their colour can only be seen with an extremely powerful microscope.

Almost colourless. These diamonds are labelled G, H, I or J. Their pale yellow hues are hardly visible to the naked eye.

Pale. Diamonds with a pale yellow colour are marked K, L or M.

Very bright. Diamonds of darker shades are graded N to R.

Light. These diamonds are the yellowest and are at the very end of the scale from S to Z.

Transparency-Clarity

Diamonds are formed by exposure to extreme heat and pressure, a process that takes more than a billion years in nature. As diamonds form, many imperfections can occur. When assessing quality in diamonds, these are called inclusions if they are internal and defects if they are external. In Lithuania, clarity is assessed by the CIBJO classification. This criterion is divided into the following categories:

Flawless (LC). Without any internal or external defects - the rarest.

Very, very small inclusions (VVS1, VVS2). Also very high quality diamonds, with flaws only visible under high magnification microscopes.

Very small inclusions (VS1, VS2). The flaws of such diamonds are also not visible to the naked eye.

Minor inclusions (SI1, SI2). Only rarely are flaws visible to the naked eye.

Visible inclusions (P1, P2, P3). The flaws in such diamonds are clearly visible to the naked eye.

It should be noted that focusing on how the diamond looks at 10x magnification is not always correct. Most people are concerned with how a diamond looks to the naked eye and not how it looks under a microscope. Some inclusions, which are easy to see at 10x magnification, have no effect on the visual appeal of a diamond to the naked eye. Others are harder to see at 10x magnification, but they are detrimental to the visual appeal of the whole diamond. This is therefore the most difficult characteristic of diamond appraisal, as it may also depend on the subjective viewpoint of the buyer. 

Carat

The carat weight is the standard unit of measurement for diamonds. It is derived from an ancient unit of measurement called the rose seed. These seeds were roughly the same size and weight and were therefore used as early units of measurement. A modern carat is equivalent to 200 mg.

The weight of a carat is closely related to (but not identical to) the dimensions of a diamond. The dimensions of a diamond on its surface are often referred to as the area. The width of a perfectly cut 1,0 ct round brilliant is approximately 6,4-6,5 mm.

Some diamond shapes appear larger than others when they weigh a certain carat. For example, a 1ct cushion-cut diamond usually looks smaller than a 1ct round, while a 1ct emerald looks larger. This is because different shapes of diamond accumulate their weight differently: some expand widely, such as trillions, while others, such as round diamonds, expand deeply to catch the light.

Be especially careful when comparing the size of a diamond with that of other gemstones. Different gemstones have different densities and therefore different carat weights, even in the same dimensions. For example, a 6.5 mm round diamond might weigh 1ct, while a 6.5 mm round alexandrite might weigh 2ct! Therefore, when it comes to non-diamond gemstones, we always recommend using the mm size as well as the carat weight.

Certification of diamonds

The characteristics of a diamond are confirmed by a diamond certificate. In Lithuania, this service is provided by the Lithuanian Assay Office. Other globally recognised grading laboratories include the aforementioned GIA, the European Gemological Laboratory (EGL), the International Gemological Institute (IGI) and the American Gemological Society (AGS).