Buying Diamonds: 4CS, Diamond Cuts & Shapes Guide

When it comes to buying diamonds, the 4Cs are the most important characteristics to consider. Here, we’ll explore in detail what the 4Cs mean, the differences between them, as well as the most popular types of diamond shapes, so you can be fully prepared before purchasing.

The classification and value of a diamond is determined by four factors - the 4 Cs; Colour, Clarity, Cut and Carat. It is not possible to accurately value a stone based on any of these factors in isolation.

Carat for Diamonds (and indeed all other gemstones) is a measure of the weight of the stone - unlike with gold, where the term refers to its purity.

The term carat is derived from the word 'carob'; owing to the uniform size of the seeds found on the Carob tree which were traditionally used on precision scales as units of weight for small quantities of precious gemstones.

The weight of an average carob seed is 200 milligrams. The weight of one carat is precisely 200 milligrams, or 0.2 grams. Smaller diamonds, generally those under one carat, are also referred to in points, whereby 100 points make up one carat. Therefore a half carat stone can also be described as 0.50 points, and a 3/4 carat stone has 0.75 points.

It is worth noting that the price of a diamond does not increase on a linear scale with increases in the carat weight of a diamond. There are various weights above which there is a steep increase in value. As a carat is a unit of weight and not size, meaning that two one carat stones may appear to be different sizes.

Colour in this context does not refer to a diamond of specific colour (these are treated separately and known as 'fancy coloured diamonds'), but to diamonds which are white with a faint tinge of yellow or brown.

The hint of colour is often so slight that only trained eyes are able to detect it, and it definitely does not detract from the beauty of the stone. Pure, colourless stones are incredibly rare meaning that the value of a stone will usually increase or decrease according to how much 'colour' is present.

The cut of a diamond, often called the make, depends upon the proper proportions of the cut stone and the accurate alignment of the facet edges. In order to reflect all of the light entering the stone from the front, a well cut diamond should have proportions as near as possible to a predetermined ideal.

There are a number of different shapes of cut. Brilliant, Princess, Navette, Asscher, Emerald and Pear are some popular examples.

Despite what many believe, the terms ‘diamond cut’ and ‘diamond shape’ have different meanings. Diamond cut refers to how the diamond has been cut and polished, whereas the diamond shape is the shape the gem has been cut into.

The process of diamond cutting turns the rough stone into a faceted gem. So, the diamond cut refers to the overall proportions of the diamond and is, arguably, the most important C when it comes to deciding its value and price, as the cut of a diamond directly impacts its beauty and ability to reflect light.

The various factors that impact the cut of your diamond are the proportions, symmetry, brilliance, fire, scintillation and finish. All of these factors will determine the quality of the diamond cut and its reflectiveness. The finer the diamond cut, the better the brilliance and sparkle will be.

The cut proportions of a diamond will impact the gemstone’s ability to reflect light and produce dazzling brilliance. These proportions, the table, width and depth, are often based on the ratios between the size, angle and shape of the diamond’s facets. However, it’s important to remember that different diamond shapes will have different proportions.

The diamond table, the flat view from the top, is calculated by dividing the width of the top surface area by the width of the entire diamond. If the percentage is too big, the light won’t reflect off the diamond’s angles and facets. If it’s too small, the light will be trapped inside the diamond.

The width of the diamond is calculated by measuring from one end at the widest point to the other. This information is important to determine the length-to-width ratio of the diamond and how proportionate the diamond is overall so it can be made into its intended shape.

The depth of the diamond is the height from the culet to the top of the table - measured in millimetres. Generally, a lower depth will appear larger than it is because of the increased width. However, if the depth is too low, it can cause a slightly darker appearance as it’ll struggle to reflect the light.

Symmetrical diamond's facets 

The symmetry of a diamond refers to how precise the facets align. Facets are tiny mirrors within the diamond that help reflect the light and are controlled by the manufacturing process. The size and placement of the facets impact the sparkle and brilliance of the diamond, so diamonds with perfect symmetry produce the most sparkle.

Inside the diamond will be a number of facets, which are essentially tiny mirrors that bounce the light around to create excellent sparkle. These often surround the diamond’s table, and the symmetry of the diamond mirrors will impact how well the diamond reflects light.

Diamond windows are the part of the facet that enables the light to enter and exit a diamond, which is how you see it sparkling.

Before the brilliant cut, which has 58 symmetrical facets, diamonds almost always had step facets. Step facets create a sleek and sophisticated design but don’t produce as much fire and brilliance as brilliant cut facets. However, diamond steps are still popular in shapes, such as the Asscher cut.

Diamond brilliance

The brilliance of a diamond is the brightness of the white light reflection. This means that when you look at a diamond under a bright light, it should reflect an almost endless amount of stunning white light. If a diamond isn’t symmetrical, the diamond will look dull instead.

The diamond’s fire refers to the dispersion of coloured light reflecting off the table and facets. When looking at a diamond in the light, you should see some coloured light reflection. A well-cut diamond will have both brilliance and fire.

The scintillation of the diamond is the flashes of sparkle when the light moves around the facets. Ideally, a large amount of scintillation is desirable as this means the diamond will sparkle more brightly when moving around. A diamond with low scintillation may appear dull.

The finishing details of the diamond include permanent treatment and polishing to improve the quality and overall condition of the facets and surface. A well-polished diamond will create a clearer stone for light to reflect easier and vividly.

Every diamond is graded on its cut quality. There are 5 grades in total, ranging from excellent to poor, that are based on the diamond’s brilliance, symmetry, polish, and fire. The better the cut, the more sparkle the diamond will have, which is why many consider the cut to be the most important of the 4Cs.