BUYING DIAMONDS – A Novice’s guide


The following is a simple outline of the key elements that affect the price of diamonds. You will probably have heard of the ‘four C’s’ – Carat , Cut , Colour and Clarity .

It is the combination of these that dictates the price, in tandem, of course, with current market forces.



The weight of a diamond is measured in carats (cts). The weight of a stone under a carat is divided into 100 ‘points’ (pts). So a half carat diamond is 50pts, a quarter carat is 25pts, etc, whereas a larger stone might be 1.50cts or 1.75cts. There is a correlation between the dimensions of a diamond and it’s weight, but you have to be careful in estimating the carat weight of diamonds as it depends on the way the diamond has been cut. Modern brilliant cut diamonds are cut to exact, calibrated proportions, so you can say that a modern brilliant cut diamond of 6.42mm diameter will weigh 1 carat. However, old cut diamonds, for example, are irregularly cut. So the diameter of the ‘table’ (top) facet will not tell you the weight of the stone, as the depth and width of the stone below the table will vary.


This is a huge subject that I can not do justice to here. In brief, the most popular cut today is the modern brilliant cut, created in 1914, with exactly 56 facets. This creates the maximum fire and ‘brilliance’ due to the precise number and angle of reflections from its facets. In antique pieces you will often find ‘old cut’ diamonds (of which there are several variations), which preceded the modern brilliant cut. Other popular cuts include the princess (square cut), pear-shaped, marquise, trillion (triangular), Emerald cut (oblong with cut corners), baguette and many others.



Diamond colour today is usually graded using an alphabetical scale from D downwards (see grading scale below). The difference between each is almost undetectable to the untrained eye and it is only when you get down to about K and L that the slight drawing of colour is obvious. The best way to look at stones is therefore to compare them with others, so you can see which is ‘whiter’ or ‘yellower’ than the next.


Clarity refers to the presence or otherwise of imperfections or marks within the diamond. It is measured using a grading scale, a simplified version of which is show below. As with colour, the untrained eye will not perceive the differences between each grade and flaws will not become obvious until you move some way down the scale. Many flaws are not visible to the naked eye, so the grading is based on the use of a 10 X lens (magnification times 10).


Diamond Replacement

Grading diamonds is a job reserved for a small number of qualified and registered experts. To the untrained (and naked) eye, there is often little to choose between many commercially available stones, apart from their size and cut. However, the colour and clarity have a huge bearing on the value of the stones, so it is worth gaining a certain level of understanding, so that you can make an informed decision when choosing stones.

Reputable jewellers should be able to help by showing you how to use a jewellers ‘loupe’ (10 X lens) and pointing out differences between stones in their stock. At the lower end of the market, stones are often referred to as ‘commercial white’ and customers are not given full details. You often see diamond jewellery being sold on the internet (and even in some shops) described as, for example, ‘a 1 carat diamond solitaire ring’, with a price. The value of a 1ct diamond solitaire ring could vary between say £1000 and £10,000 depending on the quality of the stone, so it is therefore very risky to buy diamonds in this way.

Larger and better quality stones can be bought with a Certificate, from a registered diamond grading laboratory. This provides full details of the ‘four Cs’, so you can be confident of the purchase you are making. There is normally a slight premium for a certified stone and for many purchases it may not be necessary – the important thing is that you like the stone you are buying, and trust the person you are buying from.

Finally, it is great fun to learn enough to be able to select stones for your special purchase yourself. There is nothing quite like sorting through diamonds and picking out the ones you want to wear forever!

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