Ask The Experts: How To Choose The Perfect Diamond

Heart thumping. The soft click of a ring box. Four words. A lifetime ahead of you. We know it's not easy choosing an engagement ring. Round cut or emerald? What about the 4Cs? Colour. Cut. Carat. Clarity. With our guidance, discover the fine details of diamonds and how to choose the perfect one.

16 December 2021 Editor - Ernest Jones

Radiant. Strong. Enchanting. Rare. A diamond really is the ultimate expression of love. With December 25th drawing ever closer and romance in the air, what could be more magical than a Christmas proposal? We want to make sure this moment is every bit as joyful as it should be. Combining our in-depth knowledge of quality and craftsmanship, along with the insight of our diamond expert Alexandra Zagalsky, let’s help you find a diamond ring that celebrates your story.

What do you find compelling about a diamond?

When first approaching diamonds, perhaps start by thinking about what they symbolise and what special meaning they hold with you.

For Alexandra, “there’s something to be said about the mythology of diamonds.” Captivating civilisations across the world, as Alexandra elaborates, “the ancient Greeks thought they were the tears of gods, while the Romans believed they were godly gifts offered to us mortals to protect us.”

From the journey it's undergone to become its final exquisite form to the ethereal light it radiates, a diamond ring really is a beguiling way to express your love. That’s why it’s fundamental that you find the right one that perfectly captures everything you cherish about your significant other.

What are the 4cs?

As suggested by Alexandra, learning what the 4Cs are will help you greatly with your search.

Every diamond has its own unique distinguishing characteristics by which the world judges its beauty and value. Known as the 4Cs (colour, clarity, cut and carat), these are the globally accepted standards that define the quality of a diamond. Each one of the 4Cs plays a vital role in determining the worth of a diamond, and so will help you have a clearer understand when choosing yours.


Diamonds are measured in carats, which are the measure of weight (not of size as commonly thought). To be perfectly precise, one carat is equal to 0.2 grams.

An important thing to bear in mind is that the higher the carat weight, the higher the value. However, remember to consider that the better quality of diamond is always best, whatever the weight.

Carat weight can appear differently across different diamond shapes such as round, princess, pear, oval, cushion, marquise, emerald, radiant, square or heart. A diamond may have a higher carat weight without appearing larger and two diamonds of the same carat weight can vary in size if one is cut deeper than the other. Essentially, carat weight does not necessarily indicate size.


Another of the 4Cs is the colour, which Alexandra clarifies as being much rather “the absence of colour” that signifies its worth. Diamond colour is all about what you can’t see. Diamonds are valued by how closely they approach colourlessness – the less colour, the higher their value. (The exception to this is fancy colour diamonds, such as pinks and blues, which lie outside this colour range).

The Gemological Institute of America’s (GIA) colour-grading scale for diamonds is the industry standard. As explained by Alexandra, “the most colourless, purest diamond is the D”. The scale begins with the letter D. Each letter that then follows shows an increasing presence of colour, with the scale finally finishing with the letter Z.

Z+ represents fancy-coloured diamonds. These diamonds are highly prized due to their rarity – only 2% of the world's diamonds are fancy colours.


A diamond’s cut is often thought of as shape (round, marquise, square, pear), but as Alexandra advises, “the cut of a diamond is not only its shape but also how light is optimised to make the most of the way light is refracted within the diamond.”

How well a diamond’s facets interact with light is measured by its ability to create the following desirable visual effects:

  • Brilliance: Internal and external white light reflected from a diamond creating the sparkle
  • Fire: The colours you see within a diamond because of the scattering of white light through the stone
  • Scintillation: The amount of sparkle a diamond produces, and the pattern of light and dark areas caused by reflections within the diamond.

The cut of a diamond should have a good balance of brilliance, fire and scintillation and appear full of light and life. If there are any large dark areas or patches, however, this means the cut grade will be lower.


Like snowflakes, every diamond is unique. Even those of identical cut, weight, and colour-rating might vary significantly in terms of clarity. Why? In the process of a diamond's natural formation deep within the earth, extreme heat and pressure often result in unique birthmarks. These are referred to as internal flaws (inclusions) or external imperfections (blemishes). Diamond clarity refers to the absence of these inclusions and blemishes. Diamonds without these marks are rare and known as flawless. Therefore, the fewer inclusions and blemishes a diamond has, the more valuable it is.

Clarity grade considers the size, nature, position, colour, location, and quantity of inclusions and blemishes visible under 10x magnification. For example, a stone is graded as flawless if, under 10x magnification, no inclusions or blemishes are visible. A diamond with a central inclusion will be graded more harshly than one which is located towards the girdle, even if the inclusions are the same size.

A helpful point that Alexandra touches on is that certain diamond shapes hide blemishes better than others. Round diamonds have a lot of facets which cleverly conceal imperfections, but because emerald cuts are designed in a certain way, blemishes are more prone to exposure.

Which diamond shape should I go for?

Baguette? Radiant? Oval? Heart? We want to make finding the shape of love easy for you.

For Alexandra, when choosing the shape of a diamond, consider factors such as personality, hobbies and lifestyle, which can inspire your decision.

A classic choice, a round diamond will forever be cherished due to a circle metaphorically representing the eternal, never-ending nature of love, while the marquise, which resembles the shape of lips, signifies passion and romance in a more physical form.

Beauty is in the eyes of the beholder and so we understand that not everyone wants to opt for traditional styles. Thankfully, there are an abundance of different cuts available. The princess cut – defined by its square, geometric design – exudes an architectural appeal as does an emerald cut, while the vintage-looking pear cut allow the wearer to experiment with how it is worn, for example, whether you prefer the point to face the knuckle.

Create a diamond ring made with love

If you really can’t decide what diamond ring to go for, then let’s put the creativity into your hands courtesy of Ernest Jones’ For You, By You bespoke design experience. Available in store, you can build your dream engagement ring by selecting a diamond, cut, style, setting and budget to your taste.

For something that truly celebrates the unique nature of your love, you can design a one-of-a-kind piece of jewellery from a sketch. There is also the option of restoring or reimagining an existing piece of jewellery such as an engagement ring that has been passed down the generations.

We’re here to help you every step of the way

Our advice on helping you to understand more about diamonds and their different shapes and forms doesn’t stop here. We want to help you whenever and wherever we can, so book a virtual appointment or visit your nearest Ernest Jones store where you can speak to our friendly team of experts, who will be delighted to assist you. Bright, brilliant and unquestionably beautiful, diamond jewellery is symbolic of a love that will last forever. Discover your perfect diamond online or in store at Ernest Jones today.