Diamonds - cut
Based on scientific formulas, a well-cut diamond will internally reflect light from one mirror-like facet to another and disperse and reflect it through the top of the stone. This results in a display of brilliance and fire, thereby placing well-cut diamonds higher on the Diamond Quality Pyramid than deep or shallow-cut diamonds. Diamonds that are cut too deep or too shallow lose or leak light through the side or bottom, resulting in less brilliance and ultimately, value.
Cut also refers to shape—round, square, pear, or heart for example. Since a round diamond is symmetrical and capable of reflecting nearly all the light that enters, it is the most brilliant of all diamond shapes and follows specific proportional guidelines. Ask a jeweller to find out more about these guidelines.
Non-round shapes, also known as “fancy shapes,” will have their own guidelines to be considered well-cut.

Colour
Diamonds range in colour from icy winter whites to warm summer whites. Diamonds are graded on a colour scale established by the Gemological Institute of America (GIA) which ranges from D (colourless) to Z.
Warmer coloured diamonds (K–Z) are particularly desirable when set in yellow gold. Icy winter whites (D–J) look stunning set in white gold or platinum.
Colour differences are very subtle and it is very difficult to see the difference between, say, an E and an F. Therefore, colours are graded under controlled lighting conditions and are compared to a master set for accuracy.
Truly colourless stones, graded D, treasured for their rarity, are highest on the Diamond Quality Pyramid. Colour, however, ultimately comes down to personal taste. Ask a jeweller to show you a variety of colour grades next to one another to help you determine your colour preference.

Carat
Carat is often confused with size even though it is actually a measure of weight. One carat is equivalent to 200 milligrams. One carat can also be divided into 100 “points.” A .75 carat diamond is the same as a 75-points or 3/4 carat diamond.
A 1-carat diamond costs exactly twice the price of a half-carat diamond, right? Wrong. Since larger diamonds are found less frequently in nature, which places them at the rarest level of the Diamond Quality Pyramid, a 1-carat diamond will cost more than twice a 1/2-carat diamond (assuming colour, clarity and cut remain constant).

Clarity
Cut and mounting can make a diamond appear larger (or smaller) than its actual weight. So shop around and talk to your jeweller to find the right diamond and setting to optimise the beauty of your stone.

Inclusions are natural identifying characteristics such as minerals or fractures, appearing while diamonds are formed in the earth. They may look like tiny crystals, clouds or feathers.
To view inclusions, jewellers use a magnifying loupe. This tool allows jewellers to see a diamond at 10x its actual size so that inclusions are easier to see. The position of inclusions can affect the value of a diamond. There are very few flawless diamonds found in nature, thus these diamonds are much more valuable.

Inclusions are ranked on a scale of perfection, known as clarity, which was established by the Gemological Institute of America (GIA). The clarity scale, ranging from F (Flawless) to Included (I), is based on the visibility of inclusions at a magnification of 10x.
Some inclusions can be hidden by a mounting, thus having little effect on the beauty of a diamond. An inclusion in the middle or top of a diamond could impact the dispersion of light, sometimes making the diamond less brilliant.
The greater a diamond's clarity, the more brilliant, valuable and rare it is—and the higher it is on the Diamond Quality Pyramid.