With enough diamond jewellery, you may be able to evaluate the quality and grading of diamonds yourself, but for the most part, consulting an expert is best. Diamonds are graded and assessed on the 'Four Cs,' which are carat weight, cut, colour, and clarity.
A carat is the diamond's weight, and one carat equals 0.2 grams. The cut refers to how well the diamond has been shaped and faceted–both of which impact the way it sparkles. Colour ranges from a scale of D (colourless) to Z (light yellow or brown), with D being the rarest and so most valuable. Clarity refers to the presence of inclusions (internal flaws) or blemishes (external flaws).