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When we think of diamonds we think of luxury, glitz and glamour. They may also conjure memories of loved ones wearing treasured engagement rings or dazzling cocktail watches. It is a pleasure to handle these objects of beauty but understanding them is key to valuing them.

Developed by the Gemmological Institute of America in 1953, the four C’s is a system created to define the characteristics of a diamond and in doing so ascertain its value. This grading system is extremely helpful in the auctioneering and valuing field whether assigning estimates for sale or valuing diamond jewellery for insurance purposes. The four C’s comprise, Colour, Clarity, Cut and Carat weight.


The colour of a diamond is measured with a grade on a scale of D (colourless) through to Z (light yellow). Between the grades of H to I very faint colour starts to be detected under the right conditions. The auction market favours colourless stones, with value significantly increasing the closer to D a stone is graded. There are also highly desirable fancy coloured diamonds including pink, blue and green, where increased colour intensity and saturation results in greater value. For an exact grade to be determined the stone needs to be loose and laboratory tested. At auction we provide colour estimations, if a lab report is not available, as the vast majority of the diamond jewellery we sell will be found in antique or modern settings.


The clarity of a stone in determined by close examination through a x10 loupe. The stone can then be graded into a bracket indicating the size, amount and position of the inclusions. Inclusions are imperfections naturally created during the formation process and include pinpoint mineral deposits, internal cracks (known as feathers) and clouds. When determining clarity the diamond also has to be assessed to check for any treatments the stone may have undergone which can also impact value dramatically. Treatments include fracture filling and laser drilling.


Diamond cut refers to the proportions, finish, symmetry and polish of the stone. The better the cut of the stone directly impacts the brilliance and fire of the diamond. A high quality cut will result in a head turning sparkling stone of great beauty. A poor cut, and therefore lack of symmetry, can leave a diamond lifeless and value can plummet. There are many different shapes of diamond cut ranging from the more common round through to cushion, pear, marquise and emerald to name a few. Combining a well cut stone with the desired shape means there is plenty of choice when looking to invest in an engagement ring or anniversary gift and auction can be a great place to hunt for the desired piece.

Carat Weight – Does size matter?

As always this is personal preference. Often the larger the carat weight, and therefore size, the greater the value. However, carat weight should not be favoured above the other characteristics but instead looked at in combination. A smaller stone of higher quality cut, clarity and more desirable colour can be worth many times more than a stone of greater carat weight but inferior clarity, cut and colour. Consider also that the diamond which is cut to maximise carat weight can often look smaller than the diamond that is cut for beauty due to light return not extending to the edges. In summary all four characteristics are important when assessing a diamond. They should be considered in combination with each being of high importance.

With the value of precious stones and metals currently high and millions of pounds worth of jewellery gathering dust at home in drawers, it is an ideal time to investigate the value of your jewellery. Whether buying, selling or updating an insurance valuation we would be happy to discuss your needs. We are proud to hold the current auction record in Wales for the highest selling single piece of jewellery (£34,000) showing we have the knowledge and international reach to expertly market your jewellery.

Below is a selection of diamond jewellery sold at our salerooms in the recent auctions with prices noted.

Diamonds can be valued by our qualified diamond assessor Charles Hampshire, free of charge without obligation. Please contact:

Charles Hampshire

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