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Guide to Buying a Diamond Engagement Ring: The 4C's

At Paul Sheeran Jewellers, we emphasise that the most important factor when buying an engagement ring is how it makes you or your partner feel.
Guide to Buying a Diamond Engagement Ring: The 4C's

At Paul Sheeran Jewellers, we emphasise that the most important factor when buying an engagement ring is how it makes you or your partner feel. Does it make you or them feel special? Does it make you or them smile? These are the things that will count in the long-term. 


But understandably, a diamond engagement ring is a pricey purchase. It is also likely you, or your partner, will be wearing it day in and day out for many years to come. Therefore, its quality is equally as important. 


Now, if you haven’t dealt with diamonds in the past, it is completely normal if you feel overwhelmed with the amount of choice and information out there. It can be hard to feel sure that you are choosing the right one - the one that is both beautiful enough to put smiles on faces, yet durable in order to withstand the natural knocks and bumps of daily life. So, to make things easier, we’ve put together this guide to buying a diamond engagement ring, using the famous 4C’s model for diamond quality. 


The 4C's of Diamond Quality

Historically, there had never been a set standard to determine diamond quality, until the mid-twentieth century when the Gemological Institute of America (GIA) devised the 4C’s model. Assessing cut, clarity, colour and carat, the standard is now accepted the world over by diamond merchants, jewellers and customers alike. 


So, when buying your engagement ring, these are the things to consider in order to determine the quality of the stones used in your band. 



The cut of a diamond is often mistaken for the shape. However, the two are very different aspects of the overall design and quality of a diamond. While the shape can typically be seen and recognised by an untrained eye, the cut requires a much more technical assessment.


The cut actually refers to the way in which a diamond has been crafted and, you guessed it, cut, in order to interact with light. Fundamentally, the angles, lengths, widths and depths of facets on a diamond determine how well it shines when light is reflected on its surface. 


Of course, the more a diamond sparkles, the more desirable it is. Therefore, in order to classify diamond cut quality, GIA, and now most jewellers and retailers, use a five grade scale. The classifications include Excellent, Very Good, Good, Fair and Poor. At Paul Sheeran Jewellers, we recommend diamonds that have an Excellent or Very Good cut to ensure maximum sparkle! 


But as well as sparkle, certain ways in which a diamond has been cut can impact its quality. For example, any extreme variations in girdle thickness can negatively impact a diamond’s durability, and should therefore, be avoided. 



Colour is another factor that can impact the quality of a diamond. The universally accepted GIA scale is used to measure the level of hue present in any diamond. The scale runs from D - Z, with earlier letters representing those that are purest in colour, and the latter end showing a slight yellow tint. 


The scale is broken down as follows:


  • D to F - Colourless - Colourless diamonds are the rarest, which makes them more expensive.
  • G to J - Nearly colourless - The colour is only noticeable to professional gemstone graders.
  • K to M - Faint - There is a hint of yellow that is difficult to detect to the untrained eye.
  • N to R - Very light - A hint of colour is visible to the untrained eye.
  • S to Z - Light - Diamonds can appear yellow or brown.


Note: Coloured diamonds (pinks, blues and yellows) are graded on a separate colour scale and are known in the industry as fancy coloured diamonds.



Clarity is the next indicator of a diamond’s quality. Clarity refers to the blemishes on the external of a diamond, and any inclusions in its internal. 


As diamonds are naturally made, it is extremely rare for one to be found with no blemishes or inclusions. In fact, only 1% of the world’s diamonds can be classified as flawless, meaning they have neither any blemishes nor inclusions. 


Similarly, this is what makes no two diamonds the same. Although, while they can add to the uniqueness of a stone, they can also impact the shape, colour and the way in which it reflects light, which could be translated to quality. 


The GIA scale for diamond clarity is broken down as follows: 


  • Flawless (FL) - No inclusions or blemishes visible under 10x magnification.
  • Internally Flawless (IF) - No inclusions are visible under 10x magnification.
  • Very, Very Slightly Included (VVS1 and VVS2) - Inclusions are so slight they are difficult for a skilled grader to see under 10x magnification.
  • Very Slightly Included (VS1 and VS2) - Inclusions are observed with effort under 10x magnification, but are minor. 
  • Slightly Included (SI1 and SI2) - Inclusions are noticeable under 10x magnification.
  • Included (I1, I2, and I3) - Inclusions are obvious under 10x magnification, which may affect transparency and brilliance. 


t’s important to note that the clarity of a diamond will not necessarily impact an engagement ring’s overall beauty. However, due to the difficulty to assess the factor with a naked eye, it is recommended you pose the question to your jeweller.



The carat refers to the weight of a diamond, and is measured and expressed using a points-based system. For instance, if you have been looking into diamond engagement rings, it’s likely you’ve come across terms such as 0.5ct, 1ct, 1.5ct and so on. 


A trap that many people fall into is believing the larger the carat, the more expensive the diamond. However, as you will be aware, all aspects in the 4C model help determine the value of a diamond. This may even explain why you might have seen higher carat rings for lower prices, as it is probably the case that the diamond set in it is lacking in cut, clarity or colour. 


Therefore, when buying a diamond engagement ring, it is vital to consider all aspects equally to ensure you are getting the best deal and quality diamond for your budget. 


A Lifelong Investment

With the right quality and style, you are on track to choosing a diamond engagement ring that is guaranteed to last a lifetime. And to help you along the way, we offer life-long servicing appointments to ensure your ring is maintained and cared for, and remains looking brand new, no matter how many years it has been. 


Ready to choose your dream diamond ring? Browse our collection, or get in touch with our specialist team today.