Your Guide to Diamond Grading

Your Guide to Diamond Grading

The diamond grading process is accepted worldwide as the standardised way to assess the characteristics of diamonds. Established by the Gemological Institute of America (GIA), the system is used to determine a diamond’s rarity and value. And, while we at Trilogy Jewellers encourage clients to select the perfect diamond by the way it makes them feel, we bring a touch of science to the decision and can talk you through the traditional diamond grading process.

In this guide, we’ll examine what these grades mean, where they came from and how they affect a piece’s price tag. 

A brief history of the diamond grading system

It’s said that the oldest known diamonds are more than 3 billion years old, and while various grading systems have come and gone over the last few centuries, the current GIA system didn’t come into play until 1931. Robert M. Shipley, founder of the Gemological Institute of America, noticed the industry was missing the standardisation and science needed to compare and therefore properly value diamonds.

The mission of the GIA was to “ensure the public trust in gems and jewellery by upholding the highest standards of integrity, academics, science, and professionalism through education, research, laboratory services, and instrument development.”

In the 1940s, Shipley introduced the “4 Cs” to the industry (we’ll touch more on this in the next section), which he began informally teaching to jewellers. In 1955, this became the universally recognised diamond grading system - and we still use it to this day.

Cut, colour, clarity & carat weight

Cut, colour, clarity and carat weight, also known as “the 4 Cs”, are used to evaluate the quality of a diamond. While each component measures just one characteristic, together they form a comprehensive evaluation of a diamond’s beauty, according to science.

  • Cut: The diamond’s shape, angles, symmetry, facets and finish
  • Has the largest impact on a diamond’s brilliance, fire and scintillation
  • Colour: How colourless the diamond is
  • In a white diamond, a yellow tint indicates a lower quality
  • An ideal diamond has minimal body colour, so it can reflect more true colour
  • Clarity: Describes the presence of inclusions and blemishes
  • Diamonds are formed under intense heat and pressure, which causes inclusions (imperfections inside the diamond) and blemishes (imperfections on the surface)
  • Diamonds with less inclusions and blemishes have more brilliance
  • Carat: The diamond’s weight
  • Measures the weight, not size, of a diamond

What do the clarity grades mean?

The GIA system sorts diamonds into 11 grades or categories. Size, nature, position, colour or relief, and quantity of clarity characteristics visible under 10x magnification all determine the clarity grade. At the highest point of the grading system is the flawless (FL) classification, which covers exceptionally rare diamonds. 

The accepted scale, taken from the GIA website is:

  • Flawless (FL) - No inclusions or blemishes are visible to a skilled grader using 10× magnification
  • Internally Flawless (IF) - No inclusions and only blemishes are visible to a skilled grader using 10× magnification
  • Very, Very Slightly Included (VVS1 and VVS2) - Inclusions are difficult for a skilled grader to see under 10× magnification
  • Very Slightly Included (VS1 and VS2) - Inclusions are minor and range from difficult to somewhat easy for a skilled grader to see under 10x magnification
  • Slightly Included (SI1 and SI2) - Inclusions are noticeable to a skilled grader under 10x magnification
  • Included (I1, I2, and I3) - Inclusions are obvious under 10× magnification and may affect transparency and brilliance

How does grading affect price?

It’s a common misconception amongst those without much experience in diamond buying that carat weight is the leading factor in setting the value. In fact, two diamonds can have the same carat weight and have wildly varying costs, due to differences in cut, colour and clarity.Clarity is one of the leading determinants of price, and is the assessment you should pay most attention to when buying, for example, an engagement ring. Clarity reflects how flawless the diamond is and the less imperfections there are, the higher the price tag will be. 

When it comes to colour, the less colour the better. Therefore, you can expect to pay more for a more colourless diamond. Colour is measured on a scale from D-Z, where D is the most valuable. However, colours other than white - such as diamonds containing reds, blues and greens - are even more valuable than D diamonds and can be sold for an even higher premium.

The diamond experts at Trilogy Jewellers can guide you through the buying process, in-store or over the phone. Visit us in Hatton Garden or call 0203 929 8227.


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