How to buy diamonds

Diamonds might be immortalised by such song lyrics and quotes as Marilyn Monroe’s “Diamonds are a girl’s best friend” and Zsa Zsa Gabor’s “I never hated a man enough to give him his diamonds back” but the mineral is defined by its hardiness – it is the hardest known mineral and a transparent variety of nearly pure carbon. When faceted, it is very brilliant! And hence its desirability – there are more quotes besides that convey so.

There’s also cubic zirconia, a man-made synthetic stone, which sets out to do a reasonable impression of a diamond (but doesn’t quite cut it – if you’ll pardon the pub); and rhinestones, which are not diamonds at all, a transparent and artificial gem made from glass which is usually cut like a diamond but used more for costume jewellery and buttons.

There are also, however, colourless diamonds, which typically come in yellow, brown, green, red and blue. A fancy diamond is a term used to refer to any diamond with a distinctive colour and transparency – it’s thought that green, red and blue are the most rare.

A diamond’s overall appearance, therefore, is influenced by its colour which is measured in by a range that runs from D, which is colourless, to Z, which is a light yellow. The less colour is perceived to give it higher value. Unless, of course, it’s one of the rare ones – as per the Hancock Red.

It was in April 1987 that the auction house Christie’s offered a fancy purple-red diamond at 0.95 carats as its top lot in a New York sale. For context, only one 100,000 diamonds qualifies as a “Fancy” colour and these odds become even wilder for red diamonds which are considered rare by diamond dealers to the extent that if they get to hold more than three in a lifetime they are lucky.

This particular diamond belonged to Mr Hancock, a farmer from Montana who had apparently bought it in 1956 for $13,500. The Hancock Red was offered for sale in 1987 with an estimate of $100,000 to $150,000 – and sold for an incredible $880,000, which translates as $926,000 per carat.

And the Oppenheimer Blue was the most expensive blue diamond in auction history, bought for $57,973,000 in 2016 at Christie’s Magnificent Jewels auction in Geneva. Named in honour of its previous owner Sir Philip Oppenheimer, the Oppenheimers have been leaders in the diamond industry for generations. It’s in recent years that blue diamonds have become more popular – not only are they aesthetically pleasing but they are incredibly rare. This one is classified as “Fancy Vivid Blue” by the Gemmological Institute of America, the highest colour grade and colour intensity for blue diamonds. It comes in at 14.62 carats, the largest Fancy Blue Vivid to have ever appeared at auction.

Diamonds are graded according to colour, cut, weight, clarity and brilliance – and these are all things you should take into consideration when buying them. Typically when shopping for engagement rings – which traditionally are diamonds – jewellers talk about the Four Cs : colour, cut, clarity and carat. Finding the perfect balance – which is a personal thing – of these is the key when shopping for diamonds, which is all to do with research.

First off, there are a lot of cuts: emerald cut, with all four square corners cut off diagonally and used mostly for emeralds and large diamonds; heart-shaped cuts are used for large diamonds also; brilliant cut is a faceted cut which is used specifically for diamonds – as well as transparent gems – and appears with a flat surface on top, known as the table, sloping out to the widest point and tapered to a point at the bottom. When mounted, interestingly, only about a third of the gem can be seen. It’s the number of facets and the expertise in cutting that works to increase the brilliancy of the stone, which can be oval, pear, parquise or heart-shaped.

Cabuchon cut is used for gemstones that are higher in their centre and is used often for sapphires and rubies. The cushion cut is a variation of the brilliant cut, shaped square with corners cut off and rounded in the widest part of the stone – which is also known as the girdle. It’s often used for large diamonds. As is the marquise cut – a basic oval shape with pointed ends, sometimes thought to look like a boat. It was introduced during the reign of Louis XV and named after his mistress Marquise de Pompadour.

An old mine cut refers to a brilliant cut from the 19th century that retained a substantial amount of the original stone and had a larger cutlet and smaller table compared to modern counterparts. While the oval cut is simply an oval version of the brilliant. And a pear cut is a cross between a brilliant and marquise but with one pointed end and one rounded. Again, it is favoured among large diamonds. The rose cut is a simple faceted cut and often used for inexpensive gems.

When it comes to clarity, the scale runs from IF, meaning internally flawless, to I3, for included grade 3. There are 11 grades and they take into account inclusions, which are the markings inside – sometimes these have been referred to as “nature’s birthmarks”. A diamond is more valuable the fewer inclusions it has.

And carat refers to the measurement of what a diamond physically weighs, which has been in use since 1913. 1 carat is equal to 0.2 grams.

Setting, too, is important – too fine and the stones could fall out, too heavy and the ring mount might suffocate the stone. You bought it to be seen, after all.

Types of coloured diamond include the canary diamond, a fancy diamond in yellow which is rare and expensive. While the Cape May diamond is not one at all – and actually refers to rock crystal from Cape May, New Jersey. Neither is the Herkimer diamond or Lake George diamond a diamond. Both are also rock crystal.

There have been, however, some serious diamonds through history: The Hope diamond, for example, which perhaps somewhat ironically is meant to be cursed. Currently housed at the Smithsonian – where it is meant to be the museum’s most popular attraction – the diamond is famous for its size and colour: 45.52 carats in saturated blue. It has been stolen several times and changed hands on numerous occasions, recut and reshaped. At one point it belonged to Marie Antoinette and Louis XIV and the heiress Evalyn Walsh McLean – who, after acquiring it, lost several members of her family. It was later sold to Harry Winston who sent it by mail to the Smithsonian museum. Apparently the mailan who delivered it was in a truck accident.

It’s no surprise to hear the names Elizabeth Taylor and Richard Burton in reference to diamonds. Her jewels have been among some of the highest or impressive lots in auction history. At one in 1969, Cartier paid a staggering $1,050,000 for a flawless 68.4 carat pear-shaped diamond which, the next day, Richard Burton bought for his wife Elizabeth Taylor. Following the divorce of the couple, Taylor sold the diamond to New York jeweler Henry Lambert.

And the 140.6-carat Regent diamond is thought to a beautiful stone, noted widely for its purity and size. Discovered in the early 18th century in India by a slave, rumour has it, he concealed it in a self-inflicted wound. An English sea captain promised to smuggle him and the gem out of the country but actually ended up killing him and keeping the gem for himself. Cursed, it would disappear during the French Revolution, reappearing in the sword of Napoleon I.

Diamonds were originally found only in India but now many come from South Africa and Brazil. And among the many jewellery houses that work with them, a handful are known especially for them. Harry Winston, after all, was called King of Diamonds, and De Beers is well known for its unique combination of rough and shiny diamonds, as well as brilliant diamond pieces. The former launched in 1932 – though Mr Winston had launched his first diamond business, The Premier Diamond Company, in 1920 – while the latter has over 130 years of diamond experience.

It’s all of this information – which may seem like a lot of information – that is useful to know when buying diamonds. The houses, the styles and designs, cuts, the provenance and more.

A diamond’s cut, for example, will affect its sparkle and brilliance – symmetry and polish boost magnificence; and it’s the cut that determines the symmetry of the stone’s facets, which is a jewellery term used to describe a small plane cut in a gemstone to enhance its ability to reflect the light.

Notably, the purchase of a diamond usually chimes at a time of social significance or importance, such as a wedding or engagement, birthday or anniversary. It’s a big purchase. So it’s important to choose a reputable jeweller or jewellery house. Find out as much as you can about them. And make sure you trust them.

Likewise, provenance and certification are very important when it comes to diamond buying. The GIA, which stands for Gemmology Institute of America, is well known and the most respected in the diamond industry. The diamond will be given a GIA report number which will detail its cut, colour, carat and clarity, all the relevant details.

Similarly, the provenance of the stone – how and where it is mined – is incredibly important. Suppliers should be members of the RJC, Responsible Jewellery Council, which means they are committed to the council’s Code of Practices, which is an international standard on responsible business practices for diamonds gold and platinum group metals. It also addresses human rights, labour rights, environmental impact, mining practices, product disclosure and more.

By shopping with jewellers registered with the Kimberley Process Certification Scheme, you can avoid ending up with a conflict stone, or “blood diamond” as it is also known. Established in 2000, it prevents this from happening by tracking every diamond from where it was originally mined to where it is sold. There is an estimated 99.8 per cent of diamonds among the diamond market that are conflict free as a result.

Going back to the note on buying from a reputable name, it’s good to ask around: who have friends and family bought from in the past and been impressed by? And why? Again, it is a serious purchase and not one to take lightheartedly. Speak to people first, then book some appointments – try some styles on for size (our guide on sizing and buying engagement rings will also help you on this). What’s your budget and who does best for that? The great thing is that you can do a lot of research before you even step foot in a store – websites are regularly updated to reflect what is in stock, so you can go armed with specific questions and an idea of what you want.

If buying from an auction or antique dealer, the questions regarding stone provenance and certification (and curse potential) are especially important. What’s the story behind the stone? Ultimately, once you are informed, you should be led by your heart – something you love you will treasure and wear time and again. Because diamonds are meant to be a girl’s best friend after all!

For more on diamonds read our best diamond guide