Diamonds have an enduring, universal appeal and have been used in jewellery, including engagement rings, for centuries. Diamonds are a desirable gemstone and often a status symbol signifying their owners' success. Diamond engagement rings have been popularised by the 1947 advertising campaign by De Beers, 'Diamonds Are Forever". Buying diamonds can be a significant investment and there are many factors to consider - the main criteria are the so called 4Cs used to grade diamonds: colour, clarity, cut and carat weight, which have a significant influence on a diamond's price. Here we explore the famous 4Cs.