The basis of diamond grading starts with the 4 C’s: Cut, Colour, Clarity and Carat (weight). These four factors all interplay to determine a diamond’s price. However there are many more factors to consider when purchasing a diamond that go beyond the 4C's. We discuss below.
Understanding the 4C's
Cut - This refers to the proportion and arrangement of a diamond’s facets and the skill of workmanship in the cutting of the diamond. A diamond’s brilliance, sparkle and fire are all influenced by cut. Cut grades generally range from 'Ideal' or 'Excellent' to 'Poor' and these are based on how all the diamond’s different proportions (e.g. crown height, table diameter, total depth, pavilion depth) interplay with each other. We place Cut at the top of the list as we believe it is the most important of the 4 C’s. Exceptional cutting can make a diamond of lower colour appear brighter and whiter, it can help to conceal clarity characteristics and can even make a stone appear larger than it’s normal weight.
Diamond Cut is often overlooked by customers in favour of colour, clarity and carat (size/weight). It is also the hardest of the 4C’s to understand as an immense amount of skill and knowledge goes into assessing and cutting a diamond to excellent proportions.
Choosing a well-cut diamond is as much an art as a science. For this reason we encourage buyers to beware of companies that list hundreds of diamonds online, leaving the expertise on cut up to the purchaser. It is worth paying a little bit extra to buy a diamond from a company that specialises in well-cut diamonds.
Colour - In non-fancy colour diamonds, this term actually refers to the absence of colour. The less colour in the stone, the more desirable and the higher the price. In most cases, diamond colour grading follows the GIA colour grading chart from D -Z. The whitest diamonds are graded D. Most diamonds higher than G will appear colourless.
Clarity - This refers to the amount, size and placement of internal ‘inclusions,’ and external ‘blemishes’ on the diamond. In most cases, clarity grading follows GIA’s grades from ‘Flawless’ to ‘Included,’ which contain a significant number of imperfections, many of which can be seen with the naked eye. The more included a diamond, the lower its value. Likewise, the less included, the more valuable the stone becomes as these diamonds are more rare.
Carat - This refers to a diamond’s weight. Generally, the higher the carat weight, the more valuable the diamond, however the other quality factors of cut, clarity and colour are taken into account to achieve an overall value. Prices increase at carat points. Therefore a 1 carat diamond will be considerably more expensive than a 0.95ct of the same cut, colour and clarity and a 2 carat diamond will be considerably more expensive than a 1.95ct. However it may be worth noting that a well-cut 1.95ct may appear larger than a poorly cut 2 carat diamond.
Beyond the 4C’s - other diamond quality factors
Brilliance - This is essential to a diamonds performance. Brilliance refers to a diamond's light return, that is, its ability to reflect lots of light from its surroundings. A poorly cut diamond will leak light through the stone.
Fire - Fire refers to how a diamond returns or flashes all the spectral colours, similar to how a rainbow is reflected in the sky after rain. Diamonds act like a prism and fire in a diamond is light that has been separated into individual colours reflecting back at the viewer.
Scintillation - This refers to the interplay of intense white and black/colour flashes and sparkles that a diamond will return. The contrast of dark vs light will make a diamond appear brighter overall, especially when it is moved.
Fluorescence - About 25-35% of all diamonds exhibit some form of fluorescence under UV light. Fluorescence is the glow you sometimes see when an object emits visible light. An example is the way plankton will sometimes fluoresce in the ocean under a full moon. Fluorescence is neither good nor bad but medium and strong fluorescence can give a diamond a slightly oily look and impact its value.
Lustre - This is a largely unknown quality when it comes to buying diamonds as GIA do not report a lustre grade on their certificates. It refers to the surface quality of the actual diamond crystal and its ability to reflect light. A diamond with good lustre will appear clean and crisp, with good light reflection. A diamond with poor lustre will appear milky or murky, sometimes overly white in colour.
What is the best way to buy a diamond?
It has become a trend in recent years for diamonds to be sold online with the onus on the consumer to do all the research and understand all quality factors relating to the purchase. This is no easy task, diamond buying is an enormous subject with many pitfalls for an inexperienced buyer. It can be incredibly overwhelming and stressful to decide which diamond to buy when faced with thousands of options online. For this reason, it is worth working with a trusted jeweller or gemstone dealer who will do that work for you and present you with a refined range of well-considered options.