The basics
If you are planning to join the 75% of British men who buy their "special lady" a diamond engagement ring, you will want to pay close attention to the following advice. This is not something you want to get wrong. Not only are you about to part with a substantial amount of money (all women know the engagement-ring mantra about the fiancé waving goodbye to at least a month's salary), but you are also about to purchase an object that will be a permanent symbol of the most important relationship of your life.
There are universally agreed rules on buying diamonds. Follow them and you should avoid the pitfalls.
First, a geology lesson: diamonds are 99.95% pure crystallised carbon and can be extremely old - one to three billion years old, in fact. They are the hardest naturally occurring substance known and are formed beneath the Earth's surface when crystals of diamond occur in volcano feed-pipes. When volcanoes erode down, they release diamonds from their feed-pipes into layers of gravel which are later mined. However, due to the relative rarity of this natural process, diamond mines are found in just a handful of sites around the world. In rough form, diamonds are shipped to the world's cutting centres to be shaped and polished before being set as jewellery. It is the hardness, brilliance and sparkle that emerges during this process that transforms them into a girl's best friend.
Now for a quick history lesson, as you may be curious to know where the fashion began. Legend dictates that in 1477, a lovestruck Austrian, Archduke Maximilian, came up with a gem of an idea: why not give Mary of Burgundy a diamond ring to celebrate their imminent engagement? He placed it on the third finger of her left hand - the finger believed by ancient Egyptians to have a vein that led straight to the heart. It is not known whether the marriage was a success, but you don't need to worry about that.
The Four Cs
So now that you know why you are buying an engagement ring made with a diamond, you can familiarise yourself with the "Four Cs" - cut, colour, clarity and carat. All must be considered equally when comparing diamonds, but more than any other factor, according to Tiffany and Co, it is how the diamond is cut that will determine its defining characteristic.
Cut: As the only characteristic of a diamond not influenced by nature, the cut is open to mistakes and bad practices. Cut a diamond incorrectly and the defining sparkle will be compromised. It is how the 57 or 58 facets (the tiny planes cut on the diamond's surface) are angled and sized that dictate how light reflects and exits the diamond, an effect known as its "fire". Make the cuts too deep or too shallow and the diamond will be less brilliant.
The cut will also determine the shape of the diamond. The most common shape is the round cut, but others include the emerald, the pear, the marquise, the princess, the oval and the heart shape. Ask to see all of these shapes, if only in a picture, to make sure you have covered all your options.
Colour: The most valuable and rare colour is white, that is to say, colourless. Jewellers grade absolutely colourless diamonds with a "D". The scale moves up to "Z" (don't ask what happened to A, B and C) and, between these two extremes, diamonds will display subtle coloured tones. Diamonds with a very strong and distinct colour are extremely rare and are called fancies.
Clarity: Many people get unnecessarily hung up over the clarity of a diamond. Look into most diamonds with a jeweller's loupe (magnifying eyeglass) and you will see small "inclusions", also known as "nature's fingerprints". They look like small clouds or feathers but are usually invisible to the naked eye. Inclusions can affect the diamond's fire, but they also make your diamond unique and shouldn't always be seen as a fault. Why worry too much about something you can't see, anyway? As long as the stone is graded SI1 (Slightly Included 1) or better (best and most expensive is IF, or Internally Flawless; worst is I3, or Imperfect 3), you should be all right.
Carat: The weight, and thus the size, of a diamond is measured by carat. A carat is equal to 0.2gm, or 200mgm. A carat is divided into 100 smaller units called points. For example, three-quarters of a carat is 75 points. The average size of most engagement-ring diamonds is somewhere between one carat and half a carat. Do not confuse carats with karats, the unit of purity for gold.
Any reputable jeweller will know about the four Cs and be prepared to talk you through them all without prompt when displaying diamonds. But if you don't wish to place your trust entirely in a jeweller, you should request a "cert stone" - a diamond that has been assessed, graded and coded with a laser by an independent gemmological laboratory. The type of certificate is important, as not all are universally recognised. The most internationally recognised are issued by GIA (the Gemmological Institute of America). Other popular certificates include HRD, IGL, EGL and AGS (see Diamond Certificate Issuers, right). The fee for a grading certificate varies depending upon the carat of your diamond, but for exact prices, contact a specific laboratory. And do not be afraid of organising your own certificate rather than accepting the jeweller's recommendation.
Another good reason for getting cert stones is to guard against buying "diamonds" made with substitutes. Zircon, white sapphire, topaz and quartz are natural minerals that can be nearly colourless and used as natural diamond substitutes. Synthetic substitutes include cubic zirconia and moissanite. All these are sold as legitimately cheap alternatives, but be aware that they are sometimes, albeit rarely, passed off as real diamonds.
Diamonds can also be artificially treated, most commonly by being fracture filled, irradiated or laser treated. All of this is legal, as long as it is disclosed to the buyer, but if you want a "real" and untreated diamond, guard yourself against terms such as "clarity enhanced".
How much should I pay?
This is the fifth C - cost. Obviously, how much you spend is a personal matter, but you will no doubt hear that one to two months' salary is the norm. There is one point to say about this: it seems to stem from De Beers' publicity machine. Spend whatever you like and can realistically afford. Remember that De Beers has a near monopoly on the diamond industry and has an interest in what you spend. And scotch any thoughts that a diamond ring is a sound investment. A retailer can mark up a new diamond ring by up to 100%, and it could lose half its value the moment that you leave the shop. Even with a diamond bought at the virtually wholesale rates of London's jewellery centre, Hatton Garden, it could take more than five years to regain its price.
Give her what she wants
It is all well and good knowing your IFs from your I3s, but if you don't buy her the right type of engagement ring, all is lost. Perhaps the most important piece of advice is never to surprise her with a diamond ring, and not to buy something according to your own taste.
One way to find out what she likes is to take a cue from the style of jewellery that she already owns. Does she prefer modern or traditional? Does she favour white gold, yellow gold, two-tone (white and yellow gold) or platinum (currently the most popular metal for engagement rings)? Also, how does she react to other women's engagement rings? Does she ever express an interest in a particular style when flicking through fashion magazines? The chances are, however, after a quick consultation with her girlfriends and female relatives - if you can trust them with your secret - that you will glean a fairly accurate picture of her likes and dislikes.
She will probably prefer a classic diamond solitaire - which account for 76% of all sales of engagement rings - but there are many ways to present a quality stone on a ring. Would she like a Tiffany-style solitaire in which prongs hold the diamond high? Or perhaps a basket setting, or some other low-head style? Without doubt, though, you should involve her in the decision. It may run counter to your romantic instincts, but she will thank you.
1: Buying from a jeweller
There are alternatives to buying an engagement ring from a jeweller. You could, perhaps, consider buying an antique ring from a shop or auction, but if you want a new ring it is best to visit as many jewellers as possible to gauge what is available on the market. It is worth remembering that major high-street jewellers are inevitably pricier than London's jewellery centre at Hatton Garden, so if you can visit there - many different shops, all in one street - so much the better. Consider, too, that jewellers are busiest in the run-up to Christmas and before Valentine's Day. August is traditionally their slowest month, so it may be the best time to ask for a better deal. Make sure you run this checklist through your head every time you visit a shop:
· Does the store have a long-standing and solid local reputation?
· Do the staff evidently possess a sound gemmological knowledge? Watch out for gratuitous and unexplained jargon.
· Is the shop willing to sell you diamonds with a well-known gemmological certificate? If so, make sure you keep the original rather than a copy.
· Is the shop a member of a trade association? If so, which one?
· Will the shop present a detailed receipt with your purchase? This is key to any possible insurance claim or future repair.
· Does the shop appear to have a busy repairs service? (A good indication of customer trust.)
· Exactly which warranties and guarantees does the shop offer? Read them closely.
· Will the salesperson let you examine the diamond through a loupe and on a white background? If diamonds are viewed on a black background, the eye's perception of colour is hindered.
2: On the web
Buying diamond rings via the internet is not recommended because you should view the diamonds in person so that you can cover all of the above details. If you do choose to do so, only buy cert stones and pay special attention to the delivery terms and possible tax and duty charges if buying from a foreign-based site. But the internet does offer you a chance to do your homework. The following sites will all let you gauge what styles and prices are currently available.
3: Only for the brave
If you are really on the hunt for a good deal, then you could try some of the companies trying to break with the traditional supply chain of the diamond industry. One such company is the mining firm Rex Mining Diamond Corporation, which has a website intended to bypass the retail route and sell wholesale to the public. The address is www.rexgems.com
Alternatively, try the Hatton Garden wholesalers who normally only sell direct to retailers. In most cases they will not have any recognisable street presence, just a bell to ring, but will sell loose diamonds up to 50% cheaper than available on the high street. They won't have time for people who aren't serious and probably won't be interested in delivering much of a sales spiel, but if you know exactly what you are after, give them a try. Contact the jewellery trade associations for names and numbers to try.
What else do I need to know?
Trade associations
British Jewellery and Giftware Federation
(Tel: 0121-236 2657, www.bjgf.org.uk)
British Jewellers' Association
(Tel: 0121-237 1109, www.bja.org.uk)
Jewellery & Allied Industries Training Council
(Tel: 0121-237 1109, www.jaitc.org.uk)
National Association of Goldsmiths
(Tel: 020-7613 4445, www.progold.net)
Gemmological Association and Gem Testing Laboratory of Great Britain
(Tel: 020-7404 3334, www.gagtl.ac.uk)
Diamond Information Centre (sponsored by the Diamond Trading Company, part of the De Beers Group)
(Tel: 020-7404 4444, www.uk.forevermark.com)
Diamond certificate issuers
Gemmological Institute of America Inc (GIA)
(Tel: 001 760 603 4000, www.gia.edu)
Diamond High Council (HRD)
(Tel: 0032 3 222 0511, www.diamonds.be)
European Gemmological Laboratory (EGL)
(Tel: 020-7916 3519, www.egl.co.za)
Independent Gemmological Laboratories, Inc (IGL)
(Tel: 001 212-557 0111)
American Gem Society (AGS)
(Tel: 001 702-233 6120, www.agslab.com)
Ethics watch
Do you really want a ring set with a diamond if the money you have paid for it is helping to arm a rogue government, or a militia group with a questionable human rights record? Unfortunately, the locations of some of the planet's key diamond mines happen to coincide with the locations of some of the world's bitterest conflicts, and those in control of the gems don't always invest their profits ethically.
Sierra Leone is perhaps the most infamous hot spot at present, but the diamond trade has been linked by the UN to troubles in other African states including Rwanda, Angola, Liberia, the Central African Republic, Congo-Brazzaville, Uganda, Ghana, Namibia, Mali, Zambia, Burkina Faso, Guinea and the Ivory Coast.
The UN has also criticised Switzerland, not a diamond-producing nation but a diamond free-trade area, for its role as a transit point for almost half the rough diamonds entering Britain. Antwerp, the "diamond capital of the world", is also criticised for "facilitating" the trade in so-called "blood diamonds".
As consumers, we are helpless when it comes to establishing the true origin of a cut diamond. "After the diamond is cut," says Stephen Kennedy, the laboratory director at the Gemmological Association and Gem Testing Laboratory of Great Britain, "there is no way of knowing the origin of source."
Kennedy's only advice is to be suspicious of dealers who suggest otherwise. The UN's advice is to apply consumer power by asking about the source of origin. That way the message might finally get across to an industry badly in need of better self-regulation.
· The next in the How to Buy series, on bicycles, will be published on February 27. A collection of these guides will be published in a Guardian book in the summer.