The rough and the smooth of valuing Diamonds

The rough and the smooth of valuing Diamonds

By Heidi Kjeldsen - 24th February 2016

We immediately think of rarity and quality when valuing diamonds, however, sometimes this is not always the case…

Diamonds, like other precious gemstones, have a number of determining factors which are taken into account for the purpose of valuation; there are excellent stones, unique and rare examples, and then there are many Diamonds which are imperfect and offer little value.

There are a also a few attributes to consider when purchasing Diamond jewellery, especially if in the long term you hope that the jewellery will retain its value, or even appreciate in value.

When considering the value of Diamonds there are four main classification factors often referred to as the four Cs: Cut, Colour, Carat and Clarity, with the finer examples of Diamonds possessing higher grades of each characteristic.

What are the factors considered when valuing diamonds?

There are many factors taken into account when valuing diamonds

The cut of a Diamond can have a vast impact over the value of a stone. The cut does not necessarily have a direct link to the shape of the Diamond, but is more to do with the finish and is as a result of the craftsmanship employed when cutting the stone. Diamonds which have been cut too shallow or too deep will not reflect the majority of the light out of the top of the stone, rather allowing light to emit from the stone’s sides and even bottom, which will lessen the sparkle and thus affect value.


The absence of colour within a white Diamond impacts directly to its value. A white Diamond containing no colour at all will have a higher value than one which has a slight hue. This colour scale is measured and marked with letters from D to Z, with the letter D denoting a Diamond with no colour, while Z indicates the greatest presence of colour in which a stone is still considered to be a white diamond. A stone at that end of the colour scale is then considerably lower in value.


The weight of a Diamond is referred to in carats. One carat weighs 200 milligrams, or 0.20 grams. Diamonds with a greater carat weight are more valuable than the more common, smaller examples. The largest white Diamond (as yet) found and cut is the Cullinan I Diamond, weighing some 530.4 carats, having been 3,106.75 carats when uncut and mined from the Premier Diamond Mine at Cullinan in South Africa (which my husband has visited), and then cut into 105 diamonds! It can be viewed at The Tower of London, when not being worn by Her Majesty Queen Elizabeth II.


Visible flaws and even those invisible to the human eye also impact on the value of the stone. Again there is a scale which ranges from those completely flawless specimens which will carry the highest value, through to slightly “included” (flawed), to the lowest end included specimens. Diamonds with a clarity categorised as included will very rarely see any significant appreciation in value.

Other factors to take into account when valuing diamonds

Heidi Kjeldsen Jewellery diamond fire ring
The diamond in this ring was so hardwearing that it withstood the immense heat from a house fire and I was able to recreate the ring for my client without so much as a scratch on the diamond.

There are many factors even within the categories above which should be considered when a professional is valuing diamonds. For example the type of inclusion (flaw) inside a Diamond, which makes up the internal characteristics of the stone, has a bearing on where the Diamond sits on the Clarity scale. Inclusions may take the form of tiny cavities, internal graining, clouding and other included crystals or minerals.

The blemishes on the surface of the stone are also taken into account, whether they are natural or as a result of human activity such as polish lines and scratches, chips, breaks and other defects. All the decisions on the grade of a Diamond are made when the professional valuer views the stone at 10x magnification, or higher, and then checks all of the above criteria and more. A high grade Diamond will rarely depreciate in value and as sources of natural Diamonds (untreated Diamonds) deplete, the demand and joy of owning these precious stones inevitably will rise.

Diamonds also occur naturally in red, pink, blue and yellow colours, with red being the rarest, and blue and pink less rare. Red and blue Diamonds have the greatest potential for being the most highly regarded at present, with the potential for red Diamonds to as much as double in cost the next five years.

Having a professional grade certificate for a Diamond also increases the desirability of a stone, as a certificate offers physical proof that the Diamond has received an appraisal by an unbiased, qualified expert and acts as a “passport” for that stone. Diamonds are extremely hardwearing and can withstand enormous temperatures and pressures, although they can still be damaged as they do have cleavage points which are areas of weakness.

Someone I know well had a terrible fire where the whole house was burned down. The lady of the house had some fine Diamond jewellery which she had inherited from her mother. When the ashes had cooled down her great friends sifted through the debris, and remarkably they found the Diamonds which were completely unscathed, although the gold from the ring mounts had literally burned away.  I made the ring (pictured above) with a design which was similar to the original.

If you already own a piece of jewellery which contains Diamonds and you would like it valued professionally for insurance or for sale purposes, you are welcome to book an appointment with our Valuer (see the top of the page).  The charge is £50.00 per item, unless it is a Premium item where we will advise you ahead of the Valuation.  You will receive a beautiful portfolio with photographs and a current replacement value. This will enable you to recreate your jewellery, should the unthinkable happen.

Some of my latest Diamond jewellery creations, including wedding and engagement rings, are available to view on our website or at our Mill Street shop by appointment.

If you would like a bespoke piece of Diamond jewellery created just for you then please ask about my CAD (Computer Aided Design) service, and I can source the grade and size of Diamonds to suit your requirements.

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Heidi Kjeldsen

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