Diamonds are forever (not just for Christmas)

By Sarah Modlock

23 November 2005

A kiss on the hand may be quite continental, a mini ISA may be practical but diamonds are a girl's best friend. Apparently, more of these precious gems are bought in December than any other month. So if you are treating a loved one - or yourself - to something that will continue to sparkle long after the fairy lights have gone, make sure you get the best value for money.

First discovered 4,000 years ago in the riverbeds of the Golconda region of India, diamonds have mesmerised us ever since. According to the ancient Greeks, they were the tears of the Gods. The Romans believed they were splinters of fallen stars. Not bad for something which is 99.95% pure crystallised carbon.

In fact diamonds can be between one and three billion years old and are the hardest, naturally occurring substance known to man. No wonder we love them - the idea that something so naturally strong can be so beautiful is enchanting.

Talk to me Harry Winston, tell me all about it

The guiding principles of buying diamonds are captured by the 'four Cs' - colour, clarity, cut and carat. Diamonds with the perfect combination of these are the rarest and most valuable. It is well worth getting a feel for the four Cs before you shop, even if you already have an idea of what you want, as understanding them will help you buy and appreciate your diamond.

Most diamonds appear white, or colourless. Jewellers grade absolutely colourless diamonds with a 'D' on a scale that goes right up to 'Z'. In between is a range of yellow-coloured tones, many of which may not be detected with the naked eye but which subtly reduce the value of the stone. Diamonds with a very strong and pure colour such as pink, blue, yellow, green or orange are extremely rare and are called fancies. Ben Affleck presented Jennifer Lopez with a pink diamond engagement ring and sparked a new fashion for these unusual gems.

Also largely invisible to the naked eye are any small flaws, known as 'inclusions' in a diamond. Again, the volume, type, colour, size and position of these will help determine the value of the stone. The fewer inclusions, the rarer the stone. Jewellers use a grading system ranging from 'IF' or Internally Flawless through to 'I3', the highest level of three levels of Imperfection. In between are two levels of 'VVS' (Very Very Slight inclusions), two of 'VS' (Very Slight Inclusions) and two of 'SI' (Slight Inclusions). It is unlikely that you will notice the inclusions in a stone graded SI1 or better and remember that these help make every diamond unique.

The cut of your diamond is the only aspect which is not influenced by nature and so is open to human error as well as genius. Many jewellers, such as Tiffany & Co, consider cut to be the defining characteristic. The precision with which a diamond is cut and polished determines its brilliance, or 'fire' and ultimate beauty. The arrangement and proportions of its 57 or 58 facets (tiny planes on the surface of the gem which create angles) will determine how much light can reflect within the diamond. Making the cuts too deep or too shallow will reduce the sparkle. The cut will also determine the shape of the diamond and this is a matter of personal taste. The round brilliant cut the most popular but other shapes such as emerald cut, pear shape, marquise, princess cut, oval and heart shape are widely available.

Finally, the weight of a diamond is measured in carats - not to be confused with the karats, the measure for gold purity. A carat is equal to 0.2gm, or 200mgm and is divided into 100 smaller units called points. For example, three-quarters of a carat is 75 points. A diamond in a engagement ring is typically between half and one carat in size.

Any reputable jeweller will know about the four Cs and be prepared to talk you through them. You can also request a 'cert stone' which has been assessed, graded and coded with a laser by an independent gemmological laboratory. The most internationally recognised certificates are issued by GIA (the Gemmological Institute of America). Other popular certificates include HRD, IGL, EGL and AGS. Diamonds can also be artifically treated to improve their appearance. This must be disclosed by the seller but to ensure you buy an untreated gem avoid any mention of it being 'clarity enhanced'.

Frost yourself

My good friend and trusted jeweller is Nick Gray, owner of design and repair specialists Jewelworks in the heart of London's jewellery centre, Hatton Garden. These are his tips for getting the best value for money when you buy diamonds:

•  Try to buy single diamonds at just under the carat weight you require ie. you would like a half carat so buy a .45 to.49ct stone or you want 3/4 carat so look for a .70 to .74ct. The result is that you are buying from the lower price structure but getting the same 'show' as a half or 3/4ct diamond.

•  Learn to use a loupe - the magnifying eye glass used by jewellers - and ask to borrow one in store. It's very simply and will help you to see what natural inclusions are inside your diamond. This can be brought into a negotiation or used to check the integrity of your retailer. View diamonds against a white background and look for stones that are clean in the centre as marks in the table are easier to see with naked eye. If you are buying a marked stone, look for something with inclusions at the edge.

•  There are many low-cost diamond labs in the UK now who will assess the four Cs of a diamond which is already in a finished mount. Make this a stipulation of your negotiation. You should be able to view rings which have uncerted diamonds - this gives you a price advantage as you can then ask the seller to have a cert done (2/3 days) at his cost if he wishes to conclude sale with you. Make him guarantee the outcome of the cert against a sale ie. minimum quality of stone.

•  Above all and after assessing four Cs, look for a nice 'make' in the stone - that it has been well cut and in proportion, not too deep or to shallow. A good cut or nice make will result in a lively stone with lots of fire (colourful varied spectrum under correct lighting conditions). Don't be afraid to ask the sales person if you can go outside to look at stone(s) in the daylight to check this. Once you have the basic requirements in place you should buy from the heart.

•  Consider buying a loose diamond and having it mounted. The whole process may take a few weeks so this is not an option for urgent purchases but it gives you the chance to see the stone from all angles and spot any hidden inclusions. Then you can have input on the design of the mount, making the piece more personal.

Gemmological Association and Gem Testing Laboratory of Great Britain: Tel: 020-7404 3334 or www.gagtl.ac.uk

Diamond Information Centre (sponsored by the Diamond Trading Company, part of the De Beers Group): Tel: 020-7404 4444 or www.uk.forevermark.com

Jewelworks: 0207 831 3195