With over 135 years of experience under our belts, Robert Openshaw knows a thing or two about diamond jewellery. Our knowledge and expertise means that we can help you through the minefield of information when you are considering buying a diamond.

So, what do you need to know when you are buying diamonds? The most important attributes that you need to remember are covered by the diamond 4 C’s – Colour, Clarity, Cut and Carat.


Diamonds are graded on a colour chart from D, which is the clearest and brightest of all stones with no hue to it, through to Z which would be classified as a ‘fancy colour’ stone. To the naked eye it isn’t possible to see the difference between three consecutive colour grades, so a D stone would look the same as an E or an F stone. The highest grade of stones are an H grade or higher – anything less would start to look yellow to even the untrained eye, especially if the stone is sat next to a stone of a higher grade. The clearer a stone the better the light will bounce through it and this light is what is making your diamond sparkle!


Diamonds evolved millions of years ago when carbon was heated and subjected to intense pressure deep within the earth’s core. It is an organic substance and therefore it is hardly surprising that most diamonds are flawed in some way with tiny particles buried deep within them. These fragments in a diamond are called ‘inclusions’ and the number and size of inclusions will greatly affect the value of a stone.

There are diamonds that have no inclusions and these rare items earn the classification of ‘IF’ Internally Flawless. Stones are otherwise graded as having VVS (Very Very Small) inclusions, VS (Very Small) and simply S for Small. Within the grades (other than IF) they are numbered either 1 or 2 to denote a slighter finer or harsher level of inclusions within the category. Each inclusion needs to be viewed differently. A light feathered inclusion on the edge of a diamond might not affect the sparkle whereas a large dark inclusion in the centre would certainly affect the way the light bounced through the facets and may prevent that all important sparkle.

Cut and Carat

So, we have looked at the more technical side that you need to know before you buy a diamond, but the two things that people will notice first is the cut of the stone and its carat (size).

Diamonds are cut into lots of different shapes, each one a combination of facets cut precisely to ensure that the maximum amount of light can scatter through to make your stone shine. In the industry this is called the ‘Make’ and its delicate process ensures that all important refraction of light – one degree out and the diamond will look flat and dead.

Everyone knows about the Round Brilliant Cut diamond, where 57 facets are cut for optimum light reflection and that amazing sparkle but there are lots of other cuts you could consider if you fancy something a little different – for instance a square cut Asscher, Princess or Radiant cut? Or for a more rectangular stone you could have an Emerald cut and there are more unusual cuts like Marquise or Pear shaped which will certainly ensure that the ring on your finger gets noticed!

The size of a diamond is measured by Carat. And when it comes to diamonds, size does matter! But as we have already seen, a lot more determines the price of a diamond than the size, so a small stone that is a colour D and has an IF clarity may cost more than a big stone with a large inclusion or is an L/M colour. Everyone is different as to what is important to them and every diamond purchase is a careful balance between all these factors. Generally most diamonds in commercial jewellery are up to 1.5 carats in size but they certainly do come bigger! When you are buying a diamond either online or in a store you need to compare different stones to see what size of carat you can get for your budget whilst balancing that with the other 3 C’s.


Classic round brilliant cut stone


A stunning Asscher cut with diamond shoulders


This unusual cluster has an oval diamond at the centre.