Clarity refers to diamond’s purity and is determined by presence or absence of internal or surface impurities (often called inclusions). Most of naturally formed diamonds have some imperfections in their structure, which is normal given diamonds growth process. For example, small crystals can become trapped in a diamond when it is forming. Sometimes diamond when it grows can develop irregularities in its atomic structure.
The inclusions in polished diamonds are usually invisible when looking at them with naked eye and can be detected only using a loupe or a microscope. This is because polishers aim to achieve stones of best purity without losing substantial weight.
There are internationally recognised categories of diamond purity. They range from loupe clan (flawless) to piqué (included). Internationally recognised diamond laboratories use different terms – for example the HRD (Hoge Raad voor Diamant/Diamond High Council) prefers terms ‘loupe clean’ and ‘piqué’ and the GIA (Gemological Institute of America) uses terms such as ‘flawless’, ‘internally flawless’ or ‘included’.
Diamond value increases with its purity, meaning that the fewer imperfections it has, the more expensive it is. The difference in price between purities of the same size, colour and cut diamonds can vary between 5% and 50% depending on the size, colour and clarity of the diamond. For example, the price difference between 1ct D Flawless and 1 ct D VVS1 is 25%, the difference between 1ct H VS1 and 1 ct H VVS2 is 5%, whereas the difference in price between 1 ct J P1 and 1 ct J SI2 is 32%. These are the price differences at the moment of writing this text and they can fluctuate over time, but this example illustrates how purity can affect diamond value.