All About Diamonds and the GIA 4 C's

Like snowflakes, no two natural diamonds are exactly alike. Assessing stone qualities there are over 16,000 different evaluations! What is of most importance is how a stone is going to sparkle and shine in jewellery. Most of our stones have been appraised by the GIA (Gemmological Institute of America), before being subjected to further scrutiny by our own experts who’ve been in business over 60 years. This is the important part – the diamond information in a report is no guarantee the stone is going to have a big glittering personality. Our knowledge provides our clients peace of mind that they have just secured the very best stone available for their budget. We can’t condense this amount of time into one web page, but we have supplied the basic terms, and what they are evaluated on, to provide some help when considering the options.

Looking for a loose diamond? We offer a handpicked list of exceptional stones.


Until the middle of the twentieth century, there was no agreed-upon standard by which diamonds could be judged. The GIA (Gemmological Institute of America) created the first, and now globally accepted standard for describing diamonds: Cut, Colour, Clarity, and Carat Weight.  Here is some more more about what each one means, and its influence on stone value;

1. CUT

This is most important, as it is what makes the stone sparkle. We all know diamonds are renowned for their ability to transmit light and glitter so intensely. And that is due to CUT. Of the 4Cs, this is the most complex and technically difficult to analyze. From Heirloom’s perspective, this is the one that matters most. While many sites will refer to Cut as shape (round, emerald, pear etc), a diamond’s cut grade is really about how well its facets interact with light. Precise artistry and workmanship are required to fashion a stone so its proportions, symmetry, and polish deliver the shine and sparkle only possible in a diamond.

At Heirloom, we source diamonds generally rated as ‘excellent’, meaning that the return of light is always at the very best the stone can deliver.

The GIA diagram below illustrates what we mean;

Cut evaluation


The diamond colour evaluation of most gem-quality diamonds is based on its absence. A chemically pure and structurally perfect diamond has no hue, like a drop of pure water, and consequently, a higher value. Colour is assessed in stones on a spectrum of D – being colourless, to Z, which is yellowish.

Diamond Colour


Natural diamonds are the result of carbon exposed to tremendous heat and pressure deep in the earth. This process can result in a variety of internal characteristics called ‘inclusions’ and external characteristics called ‘blemishes.’

Evaluating diamond clarity involves determining the number, size, relief, nature, and position of these characteristics, as well as how these affect the overall appearance of the stone. While no diamond is perfectly pure, the closer it comes, the higher its value.

To assess inclusions and blemishes, the industry uses a scale as follows;

  • Flawless (FL)
    No inclusions and no blemishes visible under 10x magnification
  • Internally Flawless (IF)
    No inclusions visible under 10x magnification
  • Very, Very Slightly Included (VVS1 and VVS2)
    Inclusions so slight they are difficult for a skilled grader to see under 10x magnification
  • Very Slightly Included (VS1 and VS2)
    Inclusions are observed with effort under 10x magnification, but can be characterized as minor
  • Slightly Included (SI1 and SI2)
    Inclusions are noticeable under 10x magnification
  • Included (I1, I2, and I3)

If you are interested in seeing the difference – the diagram below shows the basic principles for clarity;

Diamond Clarity


Diamond carat weight is the measurement of how much a diamond weighs. A metric “carat” is defined as 200 milligrams. Each carat can be subdivided into 100 ‘points.’ This allows very precise measurements.

A jeweller will often describe the weight of a diamond below one carat by its ‘points’ alone. For instance, a diamond that weighs 0.25 carats is a ‘twenty-five pointer.’

Diamond weights greater than one carat are expressed in carats and decimals. A 1.08 carat stone would be described as ‘one point oh eight carats.’

Larger stones are only more valuable, if their quality is good. There are a lot of large diamonds in which the cut is less than ideal, or the colour poor, or they have a lot of inclusions – these are not expensive. A large stone which is an excellent cut, and near colourless as well as having no inclusions visible is extremely valuable – because it is rarer.

Diamond Carat scale

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