The 4 C’s of choosing and buying a diamond

In 1939 De Beers sought to take the confusion out of buying a diamond by introducing the “4 C’s” to understand the characteristics of a diamond. The “4 C’s” are Carat, Clarity, Colour and Cut and is now the industry standard for classifying diamonds. The four C’s are;


Just like a dollar is divided into 100 cents a diamond is measured in carats with 1 carat (which weighs 200 milligrams) divided into 100 points with 1 point being written as 0.01 carat. For example,  when a jeweller talks about a “half carat” diamond this is written as 0.50 ct. (with the abbreviation for carat being “ct”).

A well cut 1 carat diamond will have a diametre of  about 6.5mm. The weight of the diamond will, together with the cut, determine the diametre of the diamond as we can see in the following chart for approximate diametre of a round brilliant cut diamond per carat weight;


Clarity indicates the number, size, type and placement of inclusions inside the diamond as well as external natural marks on the surface of the diamond after remaining polishing. Most inclusions just consist of uncrystallised carbon left over from the formation process of the diamond. The GIA divides clarity from best to worst; Internally Flawless (IF), Very Very Slightly Included (VVS1, VVS2), Very Slightly Included (VS1, VS2), Slight Inclusioned (SI1, SI2) and Imperfect (I1,I2, I3).  Engage Diamonds doesn’t sell Imperfect category diamonds.

IMPORTANT:  As a general rule you will find that a Modern Round Brilliant (Round) diamond should be “eye clean” (you’ll be unable to see any inclusions with the naked eye) above the Slightly Included (SI2) category but we recommend SI1 and above. Diamonds of other shapes, which usually have a larger table (the largest facet on a diamond) such as Princess Cuts, Cushion Cuts and so forth should be over “eye clean” over a Very Slightly Included (VS2) category but we recommend VS1 and above.

Please see the following chart for a helpful guide;


The GIA, the industry standard, starts it’s colour grading system at D (for diamond we presume) which is a colourless diamond and runs all the way to Z. Each letter has a defined colour and the GIA says diamonds are “colour-graded by comparing them to stones of known colour under controlled lighting and precise viewing conditions.”

Diamonds of a D, E, F colour are considered “colourless,” G, H, I, J” are considered “near colourless” while “K, L, M,” fall under the faint yellow category.  A diamond of “H” colour or above will be “white” but we recommend “G” and above depending on your budget.

The GIA colour scale is as follows;


Cut is not to be confused with the shape of the diamond. Cut refers to how well cut a diamond is. Diamonds are graded for 3 factors which make up the cut; Proportions, Symmetry and Polish with a diamond’s performance being determined by the quality of the cut. The three attributes of a diamond’s performance are Brilliance (the light refraction of the diamonds), Fire (the light dispersion of a diamond into the colours of the spectrum) and Scintillation (the flashes of light, commonly referred to as “sparkle” when a diamond is moved).

The GIA divides the Cut Scale into, from best to worst,

  • Excellent (EX)
  • Very Good (VG)
  • Good (G)
  • Fair (F)
  • Poor (P).

Cut is possibly the most important of the four “C’s” and in our opinion we would happily select a Very Good cut diamond or above for earrings or a pendant but wherever possible choose an Excellent cut diamond for an engagement ring. 

To put it simply, the better the cut the more light refraction occurs for better diamond "performance" eg sparkle and brilliance, the diagram below illustrates this;

For more information please see the GIA website information about the 4 C’s