Buying Diamonds at Auction | A Guide to the Four Cs

JEWELLERY

The Four Cs: A Guide to Diamond Buying

Kate Jolley

1 April 2024

The process of buying a diamond can be extremely daunting. When making a purchase, one would hope that a salesperson would explain all the important details in an approachable and easy-to-understand way.

As many of us have experienced in a pushy and sales-driven environment though, that is not always the case. In many instances, we end up either leaving frustrated or filled with buyer's remorse.

What is the alternative though? It seems like buying a diamond at retail is the only option when making such a large purchase. Buying diamonds at auction can seem even more daunting than facing the gauntlet of high-street jewellery stores.

Auctions don't have to be scary, however. Following our few simple diamond buying tips ahead of placing a bid, can go a very long way in making the process less stressful.

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What are the Four Cs?

The Four Cs is a phrase frequently cited in diamond discussions. Each C, carat cut, colour and clarity, represents a different aspect of diamond analysis, and we will address each one below.

THE FOUR Cs

Carat

One of the most obvious but often misunderstood factors in diamond buying. A common question is: "What is the carat weight?"

The answer is in the question, a carat is a unit of weight. This weight equals 200 milligrams and originally derived from the seeds of the carob tree. As these seeds are relatively uniform in size, they were a somewhat reliable counterweight when measuring small gemstones.

Our modern calibration system is far more accurate than this antiquated method, however, the name has stuck, and we are left with carats rather than milligrams when weighing diamonds.

What is frequently misunderstood though, is that carat weight does not immediately translate to the apparent size of a diamond. While our modern cuts do have average millimetre dimensions, it doesn't mean that a 1.00ct diamond will always conform to a particular size.

There are a multitude of factors that go into cutting and faceting a diamond and these variables impact the depth of a diamond as well as the width of a diamond which all affects the visual size when worn. This is one of the reasons it is important to either see the diamond in person or ask for a photo/video of the gemstone being worn.

THE FOUR Cs

Clarity

This relates to the internal clarity of a diamond. If anyone refers to the term ‘inclusion’ or ‘included’, clarity is what they are referencing.

Diamonds are formed when carbon is exposed to immense heat and pressure. During this process, different chemicals or even crystals can become trapped within the forming diamond (think amber and insects).

When viewed under high magnification, gemmologists can see carbon deposits or even other gems, like garnets, hidden inside diamonds. These are not inherently bad characteristics and are evidence of the diamond’s formation millions of years ago, a type of geological history that relates to the formation of Earth as we see it today.

The way we denote clarity is based on the GIA (Gemological Institute of America) system which has 6 categories that are divided into 11 specific grades. Although they may seem intimidating, these are just shortened phrases that describe how a diamond looks under 10-power magnification: I3, I2, I1, SI2, SI1, VS2, VS1, VVS2, VVS1, IF, F.

I3-I1 is the category for Included

These are diamonds that are obviously included or ‘spotted’. We like to call these ‘Dalmatian diamonds’. Viewed with the naked eye, they will show dark or grey/white spots and will not appear totally clear. Each grade relates to a level of severity, where a grade of 3 is nearly opaque and a grade of 1 will have sections of clarity.

SI2-SI1 is the category for Slightly Included

These diamonds may appear totally clear to the naked eye, but under magnification will have visible inclusions. SI1 is typically the starting grade for diamond engagement rings in the United States.

VS2-VS1 is the category for Very Slightly Included

These diamonds are even more clear, and the viewer should not be able to see inclusions with the naked eye. Inclusions should only be visible under magnification and will not be very obvious. VS is the average starting category for engagement rings in the United Kingdom.

VVS2-VVS1 is the category for Very Very Slightly Included

This category is rarely seen in high street jewellery shops unless specifically requested by a client. VVS diamonds have difficult-to-locate inclusions and will appear totally clear to the naked eye.

IF is the category for Internally Flawless

This refers to a diamond that may have a surface blemish like a scratch but has no inclusions. Diamonds of this category are just one step below flawless diamonds and are the highest category one might see in jewellery.

F is the category for Flawless

These are investment-grade diamonds, gemstones that are held in safety deposit boxes or secure vaults, not to be worn or mounted in jewellery. Even though diamonds are the hardest known material in the world, they can still be damaged and scratched by other diamonds. Too much force can also damage a diamond.

Any surface blemish will impact the category of a Flawless diamond and knock it back to Internally Flawless. While it may be appealing to own a Flawless-graded diamond, very few are ready to pay the price to own a gemstone they more than likely should not be wearing.

While these grades certainly impact the pricing of the diamond, they don’t necessarily correlate to a good or bad gemstone. So much of how we individually value a diamond is based on preference. Many people enjoy the obvious physical history that is apparent in a ‘Dalmatian diamond’ while others prefer the watery clearness of a Very Slightly Included gem.

This is another reason it is important to check in with oneself when going about purchasing a diamond. What is it that you value in a diamond’s appearance, and do you care if you can see an inclusion or not?

THE FOUR Cs

Cut

This relates not only to the shape of a diamond but also the quality of the faceting. The shape of a diamond is what gives it its name and the most common example is ‘round brilliant’.

‘Round’ is the shape of the diamond and ‘brilliant’ is the faceting style. A diamond's cut grade is determined by how well the facets are placed by the artisan. It shows how well the diamond was cut.

Diamond cutting is an art in and of itself. The rough material is rarely uniform and seeing its potential takes practice and skill. Diamonds are an unforgiving material and once a portion is cut off or polished out, it cannot be replaced. The quality of the cut is responsible for much of the beauty of a faceted diamond and is one of the most complex and technical aspects of the Four Cs.

While this certainly seems like a heavy topic, the real judge of the quality of the cut of a diamond is the viewer. There are ratios and equations that one can follow to determine if what they are looking at is a technically top-quality cut, however, the quality of faceting is apparent when the diamond is examined. A poorly cut diamond will look it.

When judging cut, the variables one should consider are brightness, fire, and scintillation.

Brightness is the white light that is reflected from a diamond. This is the light that is reflected both internally and externally and gives the white flash when light hits a diamond.

Fire is the refractive quality of a diamond when it splits light. This is what causes the tiny rainbows one might see when looking into a diamond.

Scintillation is sparkle and is caused by well-placed facets bouncing light around the inside of the diamond.

All these variables can be judged from a diamond’s face-up appearance. When a diamond is of poor cut it will appear dull or have heavy ‘extinction’ which is when light passes through a diamond without reflecting out and occurs when facets are improperly placed.

Diamond shapes that are particularly difficult to facet well are pear and oval cuts. These elongated shapes can have what are termed ‘bow-ties’ which are points of extinction that look like a bow-tie through the centre of the diamond. Bow-ties have minimal scintillation and can appear grey.

The best way to judge if a diamond is well cut and faceted is to look down at the top, rock the gem back and forth, and see how it catches and reflects the light. The most important thing to consider though, is personal preference.

Some faceting styles emphasise fire over brightness, for those who prefer the rainbow flash, while others focus more on scintillation. When purchasing a diamond either for oneself or for another person, determining personal preference and developing an opinion for the type of sparkle is just as important as having a preferred shape.

THE FOUR Cs

Colour

This is perhaps the simplest of the Four Cs as it is exactly what it sounds like. This is the colour of the diamond. The colour scale for diamonds ranges from D to Z. D represents colourless and Z represents the most colour-saturated a diamond can be without being a ‘fancy colour’.

Traditionally, colour is graded when a diamond is unmounted. The gem is placed against a white card or compared against a set of masterstones that represent the various tones in the scale.

The colour of a diamond can only be accurately graded when it is outside of its jewellery mounting because the colour of the surrounding metal can influence the apparent colour of the diamond. When purchasing a diamond, it is therefore important to consider the final look of the jewellery, yellow-toned diamonds appear warm and buttery when worn in yellow gold but show out as off-white when worn in either white gold or platinum.

Fancy-coloured diamonds are what we think of as Canary Yellow or even Pink. Diamonds are one of the few gemstones that come in a full rainbow spectrum of colour and fancy-coloured diamonds have their own grading system. Personal preference is one of the most important factors to consider when judging colour, while D is at the top end of the colour scale, fancy-coloured diamonds can sell for extremely-high prices and low-toned diamonds have their own warm charm.

Now that the categories are broken down and explained, how do we determine what is a good or bad diamond? The answer may be shocking… there are no good or bad diamonds. While it is the job of a gemmologist or diamond grader to accurately examine and assign a quality to a diamond, when purchasing a gemstone, the most important opinion is your own.

These categories and variables are tools. Clarity and colour charts inform that there are elements to be considered when going about the purchasing process, but they don’t trump personal preference. When considering the average purchasing experience of diamond shopping, having this information is imperative, it would be equivalent to purchasing a car without doing any prior research.

Much of diamond pricing revolves around rarity and these grading factors help justify this cost. It is far more difficult to find a VVS-graded diamond than it is to find an I-graded diamond. It is harder still to find a VVS1 D colour 4-carat Excellent cut diamond.

This does not however mean that you would prefer that VVS1 D colour 4-carat Excellent cut diamond over a VS2 K colour 2.40-carat antique Asscher cut diamond. When buying at a jewellery or diamond auction, it's all about your preferences. Having all the details, coupled with the expertise of our auction house specialists, will help you determine what you like. You might even find a hidden treasure.

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AUTHOR

Kate Jolley

Junior Specialist

kathryn.jolley@lyonandturnbull.com

0131 557 8844

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