The cut of a diamond determines how it reflects light, which is responsible for its sparkle or brilliance and refers to the angles and proportions of the polished stone. A well-cut diamond is cut by a skilled professional to the best proportions possible so that light will be reflected from each of its mirrorlike facets and disperse through its top. Too shallow a cut will let light escape through a diamond's bottom, causing it to appear dull, while too deep a cut will allow light to be lost through a diamond's sides, making it appear dark. It is the only one of the 4Cs that is not created naturally by Mother Earth, but is generated by the skill of an experienced craftsman. Cut is often also used in reference to the physical shape of a diamond.
Because a diamond with perfect colour and clarity could nevertheless have poor brilliance if it is not well cut, many gemologists consider this to be the most important property to note when choosing a diamond. Diamonds can carry cut grades of Excellent, Ideal, Very Good, Good, or Fair.
The traditional round cut provides a combination of the best qualities a diamond can have. The symmetry of this shape means it is capable of reflecting nearly all of the light that enters it and it therefore has the greatest potential for exuding diamond hue and brilliance. There are also other shapes that can emphasise a diamond's different features. The choice of a shape is best based on personal taste and the design of the jewellery.
No two diamonds are the same. A diamond's most distinguishing characteristics are its inclusions or 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, the greater its brilliance and value. A diamond categorised as internally flawless will have no inclusions, but this is extremely rare. Diamonds with very, very small inclusions are graded as VVS1 or VVS2. Those with larger inclusions appear lower down the grading skill. Diamonds with inclusions that are visible with the naked eye are graded I1 to I3.
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 unless stones are being compared side by side. Truly colourless diamonds (D) are admired for their beauty and rarity and are therefore more valuable than lower graded diamonds which are more widely available. The choice of preferred colour is purely down to personal taste.
The comparatively rare coloured diamonds are known as fancy colours and are also quite valuable. They range in hue from the more common yellow (also graded Z+ on the alphabetic scale) to pink, blue, green, red, and even black and white.
Diamonds that are graded D, E, and F tend to be the most expensive because of their rarity. However, any diamond you buy should have a good balance of cut, color, and clarity, so as to impart the most brilliance and dazzle possible.
A diamond's weight is measured in carats, with one carat being equivalent to 100 points. You will often see a diamond referred to as a 3/4-carat stone or a 75-point diamond. Larger stones are often more highly valued, but size should not be the only consideration--clarity, cut, and colour grade, will all impact the desirability and value of a diamond.
Diamonds, as the hardest substance on earth, are resistant to damage. However, diamond jewelry is set in different metals, and care will vary from piece to piece. The girdle can be chipped by a hard blow, making a protective setting extremely important. Diamonds should be cleaned in a solution of one part ammonia to six parts water, using a gentle scrubbing brush to remove any dirt. It is a good idea to have them cleaned once a year by a professional jeweller, at which time the security of the setting can be checked as well. Diamond jewellery should be stored in a soft cloth pouch to ensure that the stone will not scratch other jewellery.