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.

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.

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.

An excellent cut diamond is the best-rated as it will be perfectly proportional and symmetrical with the most beautiful brilliance and fire. This diamond will reflect almost all of the light, making it sparkle like no other.

A very good cut diamond is the most popular cut as it's extremely similar to the excellent cut and allows most of the light to enter to create a dazzling sparkle but at a more reasonable price.

A good cut diamond won’t have the same fire or brilliance as an excellent or very good cut, but it will still be able to reflect a substantial amount of light. This type of cut is suited to those on a budget.

A fair cut diamond reflects only a small portion of light and won’t have much fire or brilliance. Fair cut diamonds are for people who prefer a higher carat weight and are willing to sacrifice the other Cs to fit within the budget.

A poor cut diamond is a gem that has been cut too deeply and, therefore, doesn’t reflect much light. Unless you are on a very tight budget, we wouldn’t recommend diamonds with a poor cut grade, as they won’t produce any sparkle.

A diamond shape refers to the shape appearance of the gem, for example, oval, round, or pear. The shape contributes to the overall look and style of the diamond jewellery piece, with many shapes going in and out of fashion over the years.

There are many different types of diamond shapes, and while some are more popular than others, trends always come and go, and diamond shapes are forever evolving. Below, we’ll explore the most popular diamond shapes and who they’ll be most suited for, depending on their taste and preferences.

The round brilliant diamond shape is most commonly used for engagement rings as it features 58 facets, which generate the highest amount of sparkle, and offers a modern yet timeless appearance that suits every type of bride-to-be.

The princess diamond shape is the second most popular shape in the world thanks to its modern, square appearance. Ideal for diamond rings, the princess cut is also a popular choice for diamond stud earrings as the sparkle is high, and any inclusions are well-hidden.

Emerald diamond shapes feature an elongated, rectangular shape with long step cuts to give it an elegant and unique finish. This type of shape gives the appearance that the diamonds are larger than diamonds of the same carat weight.

The cushion shape diamond is similar to the round brilliant but is more square in shape, with rounded corners and large facets for more brilliance. Timeless and elegant, this shape has been a favourite for over a century and can hide inclusions well while producing great fire.

An oval diamond shape is perfectly proportioned with 58 facets and a similar brilliance to a round brilliant. This shape, when worn as a ring, helps to elongate fingers for a more elegant look. It’s also very well suited as a diamond pendant or diamond locket for everyday or special occasions.

Heart shaped diamonds are the ultimate symbol of love and are perfect to give to someone special as a ring or a pendant. This shape often features between 56-58 facets, ensuring it produces brilliant sparkle. As it's more difficult to see in smaller weights, it's recommended to choose a heart shaped diamond over .50 carats.

A pear shaped diamond, also known as the teardrop shape, is a combination of the marquise and oval, known for its rounded shape and pointed tip. This popular, elegant shape offers plenty of sparkle and is well-suited as a pendant for sophisticated events and parties.

The marquise shaped diamond is a long and narrow shape with tapered edges to give the illusion of a greater size. First commissioned by Louis XIV of France, this historic and beloved shape is ideal for those looking to maximise carat weight.

The navette diamond shape is essentially another term for the marquise shape. However, the navette is slightly narrower. Pointed at both ends with curved sides, this style will help to elongate the fingers when worn as a ring.

Asscher shaped diamonds are similar to the emerald shape as they also feature large step cuts, but have a more square appearance. This shape also has a large crown and rectangular facets, which creates a stunning brilliance and unique formation when combined with the step cuts.

Radiant shaped diamonds are square with a brilliant cut facet pattern for a distinctly modern look. This shape offers impressive brilliance and fire and is very popular for engagement rings as not only do they look beautiful, but they are also more affordable since they use more of the diamond's rough.

The baguette diamond shape is long and rectangular with either straight or tapered edges that often angle inwards. This shape is popularly used as side stones in eternity or wedding rings as they only have 14 faces and don't produce a lot of sparkle or brilliance.

The trilliant shaped diamond is one of the more unusual shapes as it comprises three equal sides with 30-50 facets and either straight or curved edges. This shape is often used as an accent stone and is popular amongst those wanting fashionable, statement-making jewellery.

At Astley Clarke we are committed to sourcing our diamonds in the most ethical and environmentally responsible manner and we adhere to the Kimberley Process to do so.

The Kimberley Process is a system put in place to regulate the trade in rough diamonds. It aims to prevent the flow of conflict diamonds; ensuring that the journey from mine, to supplier, to designer is conflict free.

We require that our suppliers and designers work within the strict rules of the Kimberley Process, and believe wholly in offering our customers conflict-free diamonds only.