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  • Writer's pictureJewellery Auctions Unlimited

Buying a Diamond at Auction

Jewellery auctions are an excellent place to consider when looking to source a diamond, and will almost always be cheaper than buying an equivalent diamond from a retail jeweller.

As with any major purchase or investment however, doing some informed research before you buy at auction will ensure you get the best value for money, no matter your taste or budget.

When it comes to diamond quality, this is determined by a system colloquially known as ‘The Four Cs’, referring to cut, colour, clarity and carat weight. Together these four factors contribute to the overall beauty of the diamond, and by extension the value of the gem.


The cut of a diamond refers to not only its shape (eg round brilliant, pear, oval etc), but the overall symmetry, proportioning and polish of a diamond.

The cut of a diamond greatly affects its brilliance; a well-cut diamond will sparkle and reflect light, whereas a poorly cut diamond will appear dull and flat.


A diamond’s colour refers to how clear or yellow it is. In general, the highest quality diamonds are totally colourless, whereas lower quality diamonds have a slight yellow tint.

Diamond colour is measured using a scale which goes from D (colourless) all the way to Z (light yellow or brown in colour).

In the case of rare ‘fancy coloured’ diamonds such as a natural pink, rarity drives the value upwards even further.


Clarity is the element that categorises the purity of the stone. Every natural diamond is unique and can have a wide variety of clarity characteristics, such as crystals, feathers, clouds, twinning wisps, chips, nicks, graining and others, and their density and position within the stone determines their clarity grade.

Clarity grades range from Flawless to Included. Whilst some inclusions may be visible to the naked eye, many are only visible with a 10x loupe. Keep in mind that these natural inclusions are what makes each diamond unique!


Diamonds are measured by weight rather than size, and therefore the heavier the diamond the greater the carat weight. Larger carat weights are generally rarer and more desirable, making them higher in value.

And Lastly...

When purchasing a diamond it is important to think about The Four C’s in conjunction with each other in order to achieve the best value for your budget. For example an E color stone might be able to exhibit SI2 clarity if the cut is good.

Our Jewellery Specialists welcome your enquiries, whether you are looking for a particular stone or if you have any questions about the auction bidding process.


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