The 4C’s of diamond grading establish the basis for valuing diamonds, but there are also a number of other factors that go into valuing diamonds which we will also briefly mention.
The most obvious factor in determining the value of a diamond is its weight. The standard unit of weight for a diamond is the ‘carat’, which is equal to 0.2 grams.
Diamonds are valued on a per-carat cost in different pricing categories, with price ‘jumps’ at certain thresholds. For example, a diamond that is 1.00 carat can be worth as much as 50% more than a diamond weighing 0.99 carats of the same quality, even though it is impossible to detect the size difference without a precise weight scale when all else is equal.
However, depending on proportions, two diamonds weighing the exact same may appear very different in size, if more weight is being held in the depth. They can also have extremely different values, as the other quality factors listed below play just as important a role.
Cut quality, also known as the ‘make’ of a diamond, refers to the proportions and finish of a diamond. This is a critical factor, which can also affect the value of diamonds by as much as 50%. Proportions and angles determine the internal reflection and dispersion of light as it leaves the diamond,
The cut determines the beauty of the diamond through its perceived brilliance and sparkle, and no two diamonds are ever exactly the same. This is one of the reasons why it’s so important to see a diamond before buying it, because the effect of the cut on beauty walks hand in hand with its effect on value.
Many diamonds are not cut for beauty however, they are cut to maximise weight retention. For example, to cut a well-proportioned round brilliant shape diamond the cutter will lose at least 50% of the rough diamond. In other words, weight is sacrificed for brilliance and vice versa. Although badly made diamonds sell at a discount in the wholesale trade, realistically the unsuspecting retail customer will pay the same price regardless of make.
The colour of a diamond is either ‘Cape Series’ or ‘Fancy Coloured’. Most gem quality diamonds are ‘Cape Series’, having a trace of yellow body colour, ranging from the colourless ‘D’ and increasing gradually in tint through the alphabet down to a light yellow ‘Z’. With the exception of some natural ‘fancy colours’, such as pink, purple, red, and blue, the colourless grades at the top of the scale are the most valuable.
The colour of a diamond must be determined under laboratory conditions by comparing it to a registered set of master diamonds through visual assessment. The differences between colours are very subtle and graded according to the International Colour Grading Scale. The DCLA laboratory has the official Registered Diamond Colour Master Set for Australia.
Diamonds are formed under immense heat and pressure deep within the earth’s crust before they are brought to the surface through volcanic activity. This process causes most diamonds to have various inclusions or imperfections such as fractures, feathers, other crystals, the list goes on. The number, size, relief, and positioning of these imperfections determine the clarity grading as established by a team of trained gemmologists in a qualified laboratory.
Grades correspond to the International Clarity Grading Scale as below. Each grade represents a range of quality; consequently, diamonds of the same clarity grade are not always equally desirable. That’s why it’s important to visually examine diamonds instead of just relying on grades when selecting diamonds. For example, in some cases, a high SI2 diamond can look better than a low SI1 diamond due to the number, brightness, positioning, and types of inclusions.
Other factors when valuing diamonds:
When all other factors are equal, round brilliant cut diamonds are more valuable than any other diamond shape. This is both because there is more rough diamond weight loss when the round brilliant shape is polished, and because it is the most popular. Other shapes also vary in popularity over time.
Transparency is the extent to which a diamond conducts light and is directly related to the effect of any cloudiness, or haziness. Contrary to popular belief, although related, transparency is separate from clarity. A diamond can be hazy or slightly cloudy and still get a high clarity grade, yet be less valuable than a highly transparent diamond. This effect can be caused by particular kinds of inclusions, such as clouds or twinning lines, as well as graining, low colour, and even fluorescence can influence the ability of a diamond to transmit light.
Fluorescence is a natural attribute of many diamonds which causes them to glow under ultra violet light (UV) which is abundant in sunlight and certain types of artificial lights. Diamonds can fluoresce various colours, with blue being the most common.
Normally fluorescence does not affect the appearance of a diamond, but in some cases it affects the transparency and the diamond appears ‘milky’ or ‘cloudy’. When present, it may significantly affect the value as well.