Diamond Grading Explained – The 4 C’s.

Diamond Grading,

We’re Uncompromising When it Comes To Diamond Grading, Painstakingly Considering More than Thirty Unique Criteria.

What makes a diamond's quality? We explain the grading criteria known as the 4 c's or carat, clarity, colour & cut.

The 4c’s Are What Determines Diamond Grading

Diamond grading criteria, also known as 4 c’s are determines the quality of a diamond. These criteria, invented by GIA are what determines diamond grading. At Guthrie’s we take diamond quality beyond the 4 c’s, however knowing how these four criteria determine diamond quality is a great place to start.

Every gem we procure we personally select for its unique characteristics.  We critique each stone, in conjunction with the 4C’s, however it is the unique qualities within the stone that determines our final choice.

Understanding the 4c’s and other terminology used in the diamond industry, will give you the confidence in discussing with us, knowing what goes into selecting the perfect diamond that meets your discerning criteria, to create the perfect engagement ring or item of fine jewellery.

Diamond Size or Carat

The first C in the four C’s, is carat. Carat is a diamond’s weight, 1 carat is equal to 0.2 grams. While carat weight does have a direct correlation to size, different shaped diamonds of the same carat weight can appear larger, or smaller. 

Round, oval and marquise cut diamonds appear larger than emerald cut, cushion and princess cut diamonds due to both their shape but also the depth each unique shape requires.

Chart Showing Sizes in Round Brilliant & Emerald Cut
Round Brilliant And Emerald Cut Diamond Sizes*

Of course the size of a diamond is one of the key things to look at when purchasing a diamond, however this alone does not make a quality diamond, the other three C’s are what really determines quality.

*Please note this size chart is for example purposes and doesn’t directly show the true size of diamonds based of the indicated carat weight.

Diamond Clarity Grades

A Diamonds clarity is a measure of the purity of a diamond. Clarity is divided into grades based on the amount of magnification required to see an inclusion. I3 is the lowest clarity grade, an I3 diamond is a heavily included stone. The highest clarity grade is FL – a flawless diamond with no inclusions.

Flawless diamonds however, are incredibly rare. Most customers choose to allow for some inclusions in their diamond. Guthrie’s don’t supply diamonds with visible inclusions, or in other words diamonds that aren’t eye clean.

Chart Showing Diamond Clarity
Clarity Grades Ranging from FL to I3

The point where a diamond becomes eye clean varies by shape, in round this can be at the SI2 grade. Emerald cuts require a much higher level of clarity – normally VS1, this is due to their large flat surface. We recommend selecting a clarity grade that is higher than required to be eye clean. This is to ensure to be absolutely sure there is nothing to detract from the diamonds natural beauty.

Finally, not all inclusions are equal, at Guthrie’s we always select diamonds with well placed. Also we never purchase diamonds with brown, green or milky characteristics.

What Affect Does Colour Have?

The next C in the diamond grading criteria is colour. Colour grades start at D, being colourless and end at Z which is a light yellow colour. 

Diamond grades can also be put into groups, Grades D, E & F are all known as colourless diamonds. Grades G, H, & I are considered near colourless, and so on. We only source diamond grades in the colourless and near colourless grades.

Chart Showing Colour Grades
Example of Diamond Colour Grades

What’s more, colour has less effect on diamond price than clarity and carat. Therefore it’s worth ensuring your diamond is colourless to the naked eye. Finally, diamonds do come in many other colours, such as yellow, pink and blue.

The colour grades for these diamonds don’t follow the same grading criteria and instead measure the intensity of colour.

How Does Cut Affect Diamond Grading?

The final grade in the 4 c’s is cut. A diamonds cut grade is by far the best way to maximise the beauty of a diamond. Out of all of the 4 c’s, cut is what most affects a diamond’s overall look. Cut, not to be confused with shape, really refers to the overall quality or make of a diamond. This quality is how accurate the cutter has made the facets into the rough stone.

Chart Showing Diamond Cut Grades
Diamond Cut Grade Examples

A diamonds cut grade can be defined by these three criteria…

Fire: is the colours that a diamond reflects; these flashes of colour are a result from the diamond creating a spectrum effect with the white light.

Brilliance: is the reflection of the white light after it hits the diamond’s facets – or angles on the surface. The greater the contrast, the higher the grade.

Scintillation: is the amount of sparkle a diamond produces, or the light source illuminating as it is moved.

Diamonds reflect the most light when their cut grade is excellent (a.k.a. ideal). A diamond with an excellent cut grade reflects nearly all of the light that enters it, resulting in an exceptional looking diamond.