The Gem Guide: Buying a Diamond

Buying a Diamond can be fun and exciting while also being scary and intimidating, especially for those choosing a Diamond for an engagement ring. One of the things I really enjoy doing is helping clients through this journey and after looking at hundreds of different Diamonds of all shapes, colours and qualities, I wanted to give you a few tips to help you choose your perfect Diamond.

What is a Diamond?

It is always useful to understand a bit of information about a gem before you go and buy one, so here is a little bit of information about Diamonds.

  • Unlike many other gemstones, Diamonds are not part of a gemstone family.
  • Diamonds are the hardest known natural material in the world, they measure 10 on the Mohs scale and are considerably harder than Ruby and Sapphire. Even though diamonds are very hard they can still be chipped but only a diamond can scratch another diamond.
  • Diamonds are not only very hard, they are also very durable which means that they are perfect for any type of jewellery, including engagement rings.
  • Colour: Colourless, can have varying degrees of yellow or brown tint. Fancy coloured diamonds include red, yellow, pink, blue and green.
  • Birthstone Month: April
  • Anniversary: 60th and 75th
Round Brilliant Cut Diamond. Credit: GIA

The Symbol of Love

In modern times the Diamond has become a symbol of everlasting love which is why nearly every engagement ring sports a Diamond and as much as it would be nice for this notion to stretch back centuries but unfortunately it only goes back to the late 1930s. The Diamond as a symbol of love was created by the De Beers Diamond group as part of a marketing campaign, this was to help retain the value of Diamonds following the discovery of the African fields in the late nineteenth century.

However there is reasoning behind why Diamonds are a great choice for an engagement ring. There is no natural material that is harder than a diamond, that means that diamonds are quite resistant to being scratched or chipped. What most jewellers won’t tell you is that hardness is only a surface feature. You also need to consider how tough the stone is, toughness is an internal feature of a stone to resist fracture or cleavage and diamonds are a tough material which should easily stand up to daily wear and tear that an engagement ring faces.

Understanding the 4 C’s

When you are looking to buy a diamond, one of the things you will undoubtedly come across is the 4 C’s, but what are they and what do they mean?

Carat – Carat is the unit of measurement we use to weigh diamonds and gemstones. A 1ct diamond is the equivalent of 0.2 grams. You may see total carat weight or TCW on some pieces for sale, this is the combined weight of all the diamonds on the piece, not the weight of the main stone. On stones that weight less than 1ct, they may be referred to as points, this is where they break the 1ct into 100 points so for example a 50pt stone is equivalent to 0.5 carats.

Cut – Many people say that this is just the shape of stone but there is a lot more to it than just the shape. The cut also refers to the quality of the cut, which is a combination of how good the proportions (this is often referred to as the quality of cut on diamond reports) are, how symmetrical the stone is and how good the polish is. All these three elements of graded as poor, fair, good, very good and excellent. If you see a diamond being sold a triple x, this means that the proportions, symmetry and polish are all excellent.

Colour – When we say colour, what we are actually talking about is how free the stone is from yellow or brown colouration. The GIA colour scale is the industry standard and it ranges from D colour at the top of the scale down to Z colour at the bottom. For fancy colour stones such as pink or blue, a different grading criteria is used. The picture below illustrates how colour changes through the different grades.

Clarity – Clarity is how free the diamond is from inclusions. An inclusion is an imperfection in the stone and these can range from very very small to large and easily to spot, other factors such as the position and the number of inclusions also impact on the clarity grade. My advice is to not buy a diamond that has a clarity grade lower than SI2 as the inclusions in I clarity stones can affect the durability of the stone.

What is the most important of the 4 C’s?

I have seen a lot of people saying that one of the 4 c’s is the most important or you should prioritise one over another. Honestly, none of them are the most important. My advice to clients is always to get the best compromise between the 4 for your budget as I feel that this way you get the best quality stone for your money.

A lot also comes down to personal preference, especially when it comes to colour as some people prefer a tint in their stone where as some prefer it to be as bright and white as possible. I say this on pretty much all my guide, when it comes to buying your perfect Diamond, buy what YOU like! Not what the sales person says is the best or what other people like, you will be the one wearing it so make sure you like it before spending your hard earned money.


I see a lot of information on the internet that having fluorescence in a diamond is a bad thing and that it can affect the colour of the diamond. The only time it impacts the colour of the diamond is if it is very strong blue fluorescence as this can reduce the yellow tint in some diamonds. If the stone has faint to medium fluorescence, this will not impact the colour of the stone but you may find that a diamond with medium fluorescence will be cheaper than the equivalent quality diamond with no fluorescence.

Don’t buy a diamond just from the report

Diamond reports are a useful tool but buying one just from the information on the report is not the best way to buy one. It is always best to view the stone in person, preferably with the guidance of someone who knows what they are looking at. The reason I say this is because I have seen diamonds that look great on the report but when you actually look at them, they are not that nice or they look dull or lifeless.

Also a diamond report is not fact. It is the opinion of an experienced diamond grader/s who have viewed the stone and it should be used as a guide only.

Avoid buying treated diamonds

Even though they are quite rare in UK, treated diamonds are still available on the market. These are low quality diamonds that have been either been fracture filled or laser drilled to reduce the appearance of fractures or inclusions. They appear to be very good value but there can be durability issues, especially with fracture filled stones and I would generally advise against buying one of these and instead go for a natural diamond.

I hope this guide has helped, so that you can make a more educated decision when purchasing a diamond.

Other posts from The Gem Guide series:

Buying a Sapphire

Buying a Ruby

Buying an Emerald