August 02, 2021

What are the four C's of a diamond?

Round brilliant halor ring with round brilliant loose edited B

What are "The Four C's?"

"The Four C's" are a term often used to describe the basic assessment of the quality of a diamond and are the four main factors which affect a diamond's price. The Four C's are:

  • Cut
  • Colour
  • Clarity
  • Carat Weight

If you are just beginning the journey of searching for an engagement ring, or would just like more knowledge about the diamond studs you are buying, we are here to help.

Carat Weight 2

Carat Weight

Let's start with the most basic of the 4 C's, the carat weight. All gemstones are weighed in carats, and 1 carat is equal to 0.20 grams.

The carat originates from the carob seed, the traditional method to weigh diamonds. These seeds all were all roughly the same size and weighed the same amount and were found in areas where the diamonds were mined. This gave a consistent and fair weighing measurement.

Today, the carat is standardised and weighs the same all over the world. One carat can be broken down into 100 points to allow precise measurements. Sometimes jewellers may refer to carat weights in points, for example a pendant may be 0.70 carats but be described as 70 points.

Colour Scale GIA 2


All white diamonds have their colours assessed on a scale from D - Z, with D being colourless and Z having the most colour. D coloured diamonds have absolutely no saturation of colour, they are like looking at an ice cube, whereas diamonds further down the scale have a higher saturation of colour which is commonly yellow but can also be brown or grey. Each letter grade has a clearly defined range of color appearance. Diamonds are colour-graded by comparing them to stones of known color under controlled lighting and precise viewing conditions.

The colour scale is split into sections:

  • Colourless - D, E, F
  • Near Colourless - G, H, I, J
  • Faint - K, L, M
  • Very Light - N, O, P, Q, R
  • Light - S, T, U, V, X, Y, Z

The cause of colour in diamonds is commonly caused by different elements in the crystal lattice, yellow is caused by nitrogen and blue is caused by boron. Red, pink and brown is caused by shear stress causing plastic deformation pushing the crystal lattice out of line, affecting the absorption of light in the diamond. Green diamonds are produced as a result of radiation which over a long period of time causes vacancies in the crystal lattice leading to red light being absorbed and green light being emitted.

After Z, diamonds enter into the "Fancy" colour range, this is the point where the saturation is higher than Z and is consistent throughout the stone.

The colour grading scale was created by The Gemological Institute of America, or the GIA. The GIA are the most prestigious diamond grading lab in the world, giving fair and impartial gradings. Prior to the D-Z scale the colour of diamonds was determined by different terms in different countries, A,B and C was commonly used with A being the best, so it was vital to start the new scale from D.

At Blackacre we find that when choosing diamonds, our clients tend to look at diamonds from D-G.

GIA Clarity


Diamonds are between 1-1.3 billion years old formed at depths of 120-150km below the earths' surface, at pressures equal to balancing the Eiffel Tower on your finger tip. This immense heat and pressure produces a unique fingerprint within each diamond and this fingerprint is referred to as clarity. Whilst growing, diamonds can incorporate other minerals such as Garnet, Topaz and Peridots as well as other diamond crystals. The immense heat and pressure can cause small fractures within the diamond crystals which are referred to as feathers. Both of these are referred to as inclusions.

Based on the amount of inclusions, diamond clarity is divided into categories:

  • Flawless
  • IF - Internally Flawless
  • VVS - Very Very Slightly Included
  • VS - Very Slightly Included
  • SI - Slightly Included
  • I - Included

From Flawless down to SI1 these stones will be "eye clean" and no blemishes will be visible unless using 10x magnification. At Blackacre we will not use diamonds in the Included range, these stones have eye visible inclusions which could effect transparency, brilliance and durability.

Diamond cut diagram


The fourth C is one that at Blackacre we deem the most important. The overall cut of a diamond can be broken down into three main subcategories, polish, symmetry and cut this ultimately will affect how light enters and exits the stone. Cut can then be further broken down into brightness (amount of light being reflected from the stone), scintillation (sparkle) and fire (the breaking up of light into its spectral colours). When a diamond is graded the symmetry and placement of facets are assessed as a judge of craftsmanship and design. When a diamond is cut well, this adds to the beauty and allure, whereas if a stone is cut poorly, even a D colour Internally Flawless stone will look lifeless.

Round brilliant cut diamonds have Cut, Polish and Symmetry grades ranging from Excellent to Poor. A round brilliant has parameters which deem the cut "excellent", whereas fancy shapes (any other than a round brilliant cut), have no fixed cutting "rules", only guidelines. Fancy shapes have symmetry and polish grades, but their "cut" is judged on a personal preference basis; for example, one person may prefer an oval which is long and slender, whereas someone else may prefer a wider and more squat outline.

We think the best way to choose a diamond is in person, not to buy off what their certificate states. When creating a bespoke engagement ring, we will always provide a selection of diamonds and gemstones to assess and view each of their qualities for yourself.

Round and trillion trilogy ring
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