Selecting the Perfect Diamond

If you are wondering how to choose a diamond, look no further than our comprehensive diamond buying guide. We explain the importance of the 4 Cs of diamond grading to ensure you obtain the best colour, clarity, cut and carat weight possible. We explain how to choose a good quality diamond for your diamond jewellery, diamond earrings, diamond necklace or engagement ring. Read our guides and look at our diamond grading charts to help in your search for the perfect diamond.


Choosing the shape of diamond that you want should be one of the first considerations. A round brilliant cut diamond is the most popular diamond cut in engagement rings, and indeed other diamond jewellery. The round brilliant cut is unrivalled in its brilliance, fire and scintillation. These optical properties are key for maximizing a diamond’s unique sparkle.

Fancy cut diamonds are any diamond cut that is not a modern round brilliant cut. These include the elegant step cuts: the emerald cut, Asscher cut, and the modified brilliant cuts: the princess cut, the pear cut, the oval cut, the heart cut and the radiant cut. It also includes historical cuts such as the old mine cut, the old European cut and the transitional cut diamond. A fancy cut diamond is the ideal choice for someone who wants something a little bit different, something geometric, fun, sentimental or historical. You name the style and there will be a fancy cut diamond that fulfills the brief.

It is beneficial to decide whether you want a round brilliant cut diamond or a fancy cut diamond from the very start of the process. This is because the fancy shapes are priced differently to round brilliant cut diamonds, and to get an accurate idea of what quality you can obtain in a specific shape for your budget, it is only fair to compare like-for-like stones.  

You may, however, find that you cannot obtain the round brilliant cut diamond of your dreams for your budget. This is when it is worth considering if one of the round or geometric fancy cuts will be suitable.


The cut of a diamond is not the shape of the stone. It is actually the quality of the faceting of the finished stone. Cut is the only one of the 4 Cs that is entirely dependant upon the craftsman. A good cut is crucial to a diamond’s sparkle and brilliance.

Round brilliant cut diamonds are graded for cut on a scale from excellent to poor. The cut grade assesses three criteria: proportions, polish, and symmetry. If the proportions of the diamond fall outside of the recommended tolerances for a well cut round brilliant cut diamond, the visual impact of the stone is lost. For example, a stone that is too shallow will let light leak out of the back facets, compromising the brilliance of the stone. Likewise, a diamond that is cut too deep will not provide anywhere near the maximum return of light. When purchasing a round brilliant cut diamond, aim for the highest cut grade you possibly can, as this is where the fire and brilliance are often lost.

Unfortunately, laboratories do not grade fancy cut diamonds for cut in the same way as a round brilliant cut diamond. As such, there are no set tolerances of angles and facet dimensions that a fancy cut diamond must adhere to. However, it is important to purchase a fancy shape with a good symmetry, and this can be assessed by examining the stone face up and comparing either half for obvious symmetry flaws.

With fancy cut diamonds, the length to width ratio is key. We have listed the ideal length to width ratio of each of the fancy cut diamonds below. Ensure that this is your top priority when purchasing a fancy cut stone as these ratios prevent the longer fancy shapes from losing light in the centre – an optical effect created by poor cut quality known as the ‘bow tie effect.’

Fancy Cut

Recommended Length to Width Ratio

Asscher Cut



Cushion Cut

1.00-1.05 for square outline

1.10 for rectangular outline


Emerald Cut


Heart Cut


Marquise Cut



Oval Cut



Pear Cut



Princess Cut



Radiant Cut

1.00-1.05 for square outline

1.20-1.30 for rectangular outline


Trillion Cut



As diamonds grow, they can contain natural impurities. They are also subject to external imperfections, such as polish marks, graining and naturals. These are known as ‘inclusions’ and the clarity grading scale assesses the diamond’s freedom from inclusions and blemishes. The GIA clarity grading scale ranges from flawless to imperfect, and selecting the right grade in between these parameters is key to obtaining a sparkling stone that is full of life.

Flawless diamonds are incredibly rare, yet it is not until the clarity grade SI2 in which inclusions can be seen with the naked eye. Therefore we suggest the following grades:

Clarity Grade

What this means for your diamond

Flawless to Internally Flawless

Obtaining a diamond with a flawless to internally flawless clarity grade is a huge investment. These clarity grades are truly for perfectionists and diamond collectors who desire the knowledge that the diamond is free from inclusions (up to 10x magnification).

VVS1 to VVS2

Diamonds in the VVS grades have an exceptional clarity. They contain inclusions that are almost invisible under magnification, even to diamond graders with years of experience!

VS1 to VS2

These clarity grades are for diamonds with inclusions that are difficult to see under magnification. These appear flawless face up, and to the naked eye.


Diamonds with an SI1 clarity grading contain inclusions that are noticeable under magnification, but are barely visible to the unaided eye or when worn. For an engagement ring, we would recommend this as the lower threshold of your clarity grade preferences.


SI2 is a grade in which the imperfections inside the stone may be visible to the wearer. This grade represents a range of clarities however, and some imperfections are certainly more unsightly than others!


The ‘imperfect’ clarity grades feature diamonds that have inclusions that are easily visible without magnification. Further down the Imperfect grades, these inclusions may affect the durability and longevity of the diamond.


For the majority of diamonds, colour is graded on a scale from colourless to tinted. These grades range from D to Z. For fancy coloured diamonds, the hue, saturation and tone of the diamonds are valued, but for diamonds on the colourless to tinted scale, a distinct lack of colour is prized.

On the scale of colour grades, D is the highest. Diamonds with a D colour are incredibly rare, as most diamonds are formed with elements such as nitrogen in the crystal structure that give an off-white to yellow tint. It is worth noting that whilst a D colour diamond would be the most technically ‘perfect’ colour, it is not until I in which colour can be seen in the stone when viewed face up.

Therefore, when browsing diamonds for colour gradings we would recommend:

Colour Grades

What this means for your diamond

D to F

These colour grades are for the purists out there! Inimitable colourless stones that are otherwise known as exceptional white and rare white.

G to I

Diamonds that are assessed as a G, H, or I colour are colourless face up, with only a slight hint of colour when viewed face down. This means that once these diamonds are set in jewellery, they will appear as colourless as those in the D-F colour grades, particularly to the untrained eye. A grade I diamond should be your lowest colour preference if you are searching for a ‘colourless’ diamond.

J to K

Diamonds in the J-K colour bracket display a slight tint of colour face up that is noticeable. This is the perfect option if you desire a warm tone to your diamond, as indeed a warmer tone may complement other jewellery and gemstones, as well as skin tones better than the cool colourless grades.

L to Z

Diamonds with a colour grading between L and Z have an obvious to definite colour to them, both face down and face up. These stones are on the cusp of a ‘fancy’ colour and may well be enhanced by setting into a yellow gold mount if you are after a stone with a warm colour.

Inspect the diamond’s fluorescence too as this factor can have a bearing on the perceived colour. A diamond with a strong blue fluorescence can appear cloudy in daylight and this is maybe not the appearance you are hoping for.

Carat Weight

The size of the diamond is signaled by its weight in carats. The higher the carat weight, the larger and heavier the diamond is. All other factors being equal, the larger the carat weight, the more expensive the diamond. This is because larger diamonds of exceptional quality are rarer than smaller diamonds of this quality. However, we would argue that carat weight is not the ‘be all and end all’ as a large unsightly stone will be less well received than a smaller stone of an excellent quality. However, this decision is down to personal preference. Perhaps you have a size in mind that you would like to purchase. In this case, it is worth balancing out the remaining three Cs to find the perfect diamond for you.

It is worth considering an unusual carat weight in order to find the diamond that is right for you. For example, if you are after a 1ct round brilliant cut diamond, considering a 0.90 to 0.95ct diamond may well afford you a better quality stone for the same price. Once the diamond is set into a ring, who is to know that it doesn’t weigh exactly 1ct? With a discrepancy in weight that small, there will be no visible difference in size once the diamond is worn.


Finally, check whether the diamond you are interested in has certification. This certification provides you with a permanent record of its properties, and a summary of the 4 Cs assessed by experienced gemologists in controlled laboratory conditions. The British Diamond Company proudly stocks diamonds with certificates from the GIA, IGI, HRD and other reputable laboratories that can give you a peace of mind when making such an important purchase.

For further assistance in choosing the perfect diamond of your dreams, contact our team of diamond specialists on 01335 453 453 or email