Understanding the 4C's:


Unlocking the Mysteries of the 4 C's: Carat, Cut, Colour, and Clarity in Diamonds - By Melissa Holt DGA

In our final blog post all about the famous 4 C's of Diamond grading we will be touching on another critical factor in a diamonds quality and style; Cut!

The cut of a diamond is really what brings a diamond to life, without cutting and polishing, most stones would simply not sparkle or appear how we'd expect. When evaluating a diamonds cut, the symmetry, polish and proportions are all taken into account, how the facets interact with light is how we measure the quality of the cut.

Lets start with an uncut diamond, and look at rough diamonds before cutting!

Uncut diamonds

Did you know that naturally mined diamonds look very different from the finished dazzling article that you see for sale in jewellery? Uncut gems when mined appear as dull pieces of frosty looking glass! The most common form for natural uncut diamonds is an octahedral shape, the stone is then cut to create facets and these are polished. The adamantine lustre of a diamond can then be fully appreciated when light bounces off of their surfaces, as well as being refracted from within the stone.

A typical octahedral rough natural diamond will usually be cut into two brilliant cut diamonds for maximum yield. This is normally a 60/40 split with one larger and one smaller stone being cut.

Understanding cut

The quality of a diamonds cut is what we judge when it comes to diamond grading, how well the cutting is executed really determines how well a stone will refract and reflect light so it's really important to consider this. The symmetry, proportions and polish of the stone all affect how it reacts with light, this is ultimately what gives a stone its sparkle.

If a stone is cut too shallow then the diamonds girdle can begin to reflect around the table, causing a ring called a 'fisheye' to appear in the stone. This is due to light entering the stone and being lost through the sides, these stones can appear dull and without much fire and brilliance.

If cut too deep the stone can appear to have a dull and dark appearance through the table, causing a 'nailhead' effect. This is caused by light being lost through the back of the diamond.

A well cut diamond is often referred to as an 'ideal cut', this is used to describe a diamond with desirable proportions for pavilion depth, crown angle, table diameter, girdle thickness, culet size and polish and symmetry grades! Each of these factors affects the overall look of the diamond and essentially how well it sparkles.

TIR - Total Internal Reflection

TIR refers to light entering the stone and being able to be reflected internally within the stone and then reflected back out and into the eye. This is all possible when the angles within the diamond are 'ideal'. Which is why it's really important to consider how well the diamond is cut when selecting the perfect stone.

Diamond shapes

Another factor to consider with cut is the actual shape of the diamond and the cut it has been made into, the most common being the Round Brilliant Cut. Other shapes include Princess Cut, Cushion Cut, Radiant Cut and Oval Cut, these are all examples of Brilliant Cut facets. Emerald Cut, Asscher Cut and Baguette Cuts are all examples of step cuts.

Some types of cut such as ovals will have what's known as a 'bowtie' effect, this is when shadows can appear on the sides of the diamond, the better the stone is cut the less obvious these effects will be.

Cut grades

A diamonds cut is graded from poor to excellent, with an excellent cut meaning that the stone is well proportioned and will be able to refract light at the perfect angle for maximum sparkle. A poor cut indicates a stone that might not appear as bright or sparkly as the proportions of the cut limit the stones ability to refract and reflect light. However Old Cut Diamonds are often given a poor cut grade, this is because they are being judged against the more modern standard of cutting and therefore can't be expected to fair up against stones cut with more modern technology. Unfortunately there isn't a separate grading system for old cut diamonds and they are graded against the same criteria as modern stones, there are many calls from within the industry for one to be developed however.

Triple Excellent

Diamonds with excellent grades for cut, polish and symmetry are often referred to as Triple X Diamonds. These stones are very desirable when it comes to modern cut diamonds and carry a premium in price as well.

There are so many factors to consider when looking at the 4C's of Diamond grading, but Cut is crucial, a diamond with the best colour and clarity can only meet its true potential when paired with a perfect cut!

If you have any questions about diamonds cut then do get in touch, our diamond expert, Melissa Holt DGA, would be very happy to help.