A diamond’s cut grade is an objective measure of a diamond’s light performance, or, what we generally think of as sparkle or shine. When a diamond is cut with the proper proportions, light is returned out of the top of the diamond (which gemmologists refer to as the table). If it is cut too shallow, light escapes out of the bottom; too deep and it escapes out of the side.
A diamond’s weight is measured in carats, with one carat being equivalent to 100 points or 200 milligrams. You will often hear of a diamond referred to as a 3/4-carat, 0.75 carat or a 75-point diamond. The larger the diamond is, the more valuable it will be.
Though diamonds come in a wide range of colours, colourless diamonds have traditionally been considered the most valuable. Most diamonds are graded on a scale using the letters of the alphabet, from D (colourless), the best grade, through Z (a light yellow). It is difficult for the untrained eye to notice such variations in colour. The comparatively rare coloured diamonds are known as fancy-coloured and are valuable, sometimes being more expensive than a D flawless diamond. They range in hue from the more common yellow (also graded Z+ on the alphabetic scale) to pink, blue, green, red. Diamonds that are graded D, E, and F tend to be the most expensive because of their rarity. Grades G, H, I and J are considered near colourless stones and are used in most jewellery items.
No two diamonds are alike. A diamond’s most distinguishing characteristics are its inclusions, marks that are often invisible to the naked eye. However, under a jeweller’s magnifying loupe or microscope they can look like crystals, tiny rivers, or clouds. A diamond’s clarity is determined by the presence or absence of inclusions–fewer inclusions mean better clarity–and how visible they are. The greater a diamond’s clarity is, the greater its brilliance and value.