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The Guide to Gemstone Grading


The Guide to Gemstone Grading

Learn everything you need to know about Gemstone Grading, including colour, clarity, cut and carat. Our expert gemologists are on hand to break-down everything you need to know.

When thinking about quality you may have heard of the 4 C’s. These stand for Colour, Clarity, Cut and Carat and are the four categories used to grade diamonds. However, Gemstones are more complex, so although the four C’s still apply, there’s a lot more to consider! Read on for your gemstone grading education.

Gemstone Colour

Colour is probably the first thing you will notice about any gemstone, be that emerald green, ruby red or a classic blue sapphire. Each gemstone type has a different chemical composition which determines the colour we see.

There are then three key factors which make up the different characteristics of each colour; hue, tone, and saturation.

Hue is the basic colour of a gemstone, and what most people mean when they say ‘blue’ or ‘pink’.

Tone is the depth of colour of a gemstone, so we describe it as light blue, or dark pink.

Saturation is the intensity of the hue, which can be soft all the way up to strong.
At Fenton, we look to source gemstones of a mid to darker tone, to ensure a rich body of colour in your gemstone with a good quality of saturation so your gemstone pops!

It’s always worth bearing in mind that the appearance of the gemstone colours can change depending on which light source you are viewing them under. We would always recommend viewing a gemstone in both natural daylight as well as a warm indoor light, to make sure you love the colour no matter what!


What is Clarity

Clarity is defined by a number of factors when it comes to coloured gemstones. Every gemstone will have a number of characteristics or features which become part of the crystalline structure of the gemstone during formation and in fact prove that the gemstone is a natural, rather than synthetic product.

These characteristics are known as inclusions and they can range from microscopic to clearly visible with the naked eye. It is important to remember that the formation of coloured gemstones is complex - many factors go into forming their brilliant and distinct colours and the same chemical traces can be more or less likely to cause inclusions in the gemstone.

Certain gemstones are more likely to display visible inclusions than others - for example it is extremely rare to find emeralds and rubies which are eye-clean (meaning magnification is required to see the imperfections). In each of these cases this is due to natural processes in the formation of each gemstone and should not be viewed as a defect, but rather as part of your gemstone’s formation history. By contrast, we can reliably and confidently source eye-clean aquamarines, garnets and sapphires for example so if you are very sensitive to inclusions then we would recommend going for one of these gemstones over an emerald or ruby.

Some dealers will label gemstones as AA, AAA or AAA+ in an attempt to define quality, however these are not universally accepted definitions and as such should not be seen as firm indicators when assessing the quality of your gemstone. This is still an undocumented art, as much as a science so it is best to find a jeweller you feel comfortable with to guide you through the process.

Gemstone Cut (AKA Shape)

All Gemstones of a significant size are cut by hand. This is because each crystal is unique, and the lapidary (stone cutter) will choose how to cut the stone to best maximise colour, clarity, life and sparkle. Gemstone cutting is usually practised by skilled local artisans who have passed the skill of cutting on from generation to generation. Symmetry is undoubtedly important, however if you notice some irregularities in your gemstone, it is likely because your cutter has used their knowledge to cut your gemstone such that other important factors such as the surface colour are even and enhanced.
At Fenton, we offer 4 different cuts: oval, emerald, round and cushion. They come in five different sizes, depending on the style of the ring you choose. 

Oval Cut
Oval gemstones are faceted to allow for maximum sparkle and lustre. It is a great option if you are looking for both surface area on the finger and maximum sparkle, as the oval is longer than the square cushion or round cut, but more sparkly than the emerald cut.

Our Sizes: 7x5mm, 8x6mm, 9x7mm, 10x8mm, 11x9mm, 12x10mm

Round Cut
The round cut, similarly to the oval cut, is faceted in order to maximise the sparkle of the gemstone.

Our Sizes: 5mm, 6mm, 7mm, 8mm, 9mm, 10mm

Cushion Cut
The Fenton cushion cut is square in shape, but with rounded edges rather than sharp, straight corners. This blends the geometry of the square with the softness of the round or oval cuts.The Faceting also allows for maximum sparkle.

Our Sizes: 5mm, 6mm, 7mm, 8mm, 9mm, 10mm

Emerald Cut
Emerald cuts are ‘step cut’, which means there are fewer facets than the other cuts, making the emerald cut more subtle with more of a focus on showcasing the clarity, rather than sparkle of the gemstone. Unlike the above cuts, the emerald cut is less forgiving when there are inclusions in a gemstone.

(Fun fact: the emerald cut was named so because it was originally created for an emerald. The cut was created to show off the colour of these fantastic gemstone by allowing long “window facets”) 

Our Sizes: 7x5mm, 8x6mm, 9x7mm, 10x8mm, 11x9mm, 12x10mm

What Is Gemstone Carat (AKA Weight)

The word “carat” in connection with a gemstone refers to its weight. For a simple conversion, there are five carats to one gram. Whilst the carat weight is a good indicator of the overall dimensions of a gemstone, it does not guarantee the dimensions.

As we have already noted, gemstones are cut by hand and each cut is dependent on the individual stone. This means that the carat weight for two stones of the same dimensions may vary, as for example, one stone may be slightly deeper than the other.


This is why at Fenton we evaluate our gemstones by their diameter instead of their carat weight, as it is a more accurate judge of the overall size that you will see on your finger! You can find out more about our gemstone sizes here.

Gemstone Choice And Care

The most important C’s - choice and care!
Coloured gemstones are more unique and complex than diamonds and as such it’s important to find a jeweller who will listen to you carefully and help guide you through the maze of the 4 Gemstone C’s to arrive at the perfect choice for you.  

Our Concierge team (the best ‘C’ of all!) are here to do just that so if you are contemplating an coloured gemstone then please reach out today! You can also now book a consultation online here.


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