The most important factor of the four Cs is how the diamond is cut. The colour, clarity and carat of the diamond are predetermined; but it only displays its full brilliance once it is cut to the right proportions. This depends primarily on the expertise and experience of the diamond cutter, who can turn a raw diamond into a work of art.

The type of cut is determined by the natural shape of the raw diamond. Brilliant diamonds are only those that have been cut into a round shape with at least 57 facets. Grading the cut quality of a diamond also takes into account the symmetry of the facets, the proportions, the size of the table (the largest of the 57 facets) and the total depth of the diamond. A good cut releases a diamond’s inner sparkle. The light is reflected from one face to the other and reflects back out through the surface of the stone.

The third quality criterion of the four Cs is colour. Experts in grading diamonds rate the colour of the stones on a scale from D to Z. Specialist retailers refer to diamonds with a colour grade from D to H as white diamonds. From grade I, the stones have an increasingly yellowish hue. Although diamonds are usually encountered in their transparent form, a stone of flawless transparency is very hard to find. Even uncut diamonds have yellowish hues. Fancy colour diamonds are just as rare as flawlessly transparent diamonds. They have colours outside of the D to Z scale and come in all shades – red, orange, yellow, green, blue, purple, brown, grey and black.

For the casual observer, a higher colour grade is the key factor. For example, even the untrained eye can distinguish between a D- and G-grade colour, while the clarity of a diamond can only be determined under 10-fold magnification. This is the only way to determine the presence of inclusions and other factors that inhibit clarity.