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How to buy a diamond

When you're buying the bling for your intended's engagement ring, do your homework first to make the perfect choice.

single diamond with reflection

On average, Australian couples will spend $5134 on an engagement ring, according to the 2018 Australian Wedding Industry Report, but it's nearly impossible for most of us to judge the real value of a diamond.

Without expert understanding of diamonds, synthetics and simulants, you might find you're paying too much for a stone which isn't what you think it is.

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Diamond buying advice

When you're choosing a diamond – especially if it's for something special like an engagement ring or wedding band – it pays to keep the following advice in mind:

  • Look for jewellers that are members of the Jewellers Association of Australia and/or Diamond Guild Australia – both have a code of ethics committing members to ethical selling practices.
  • Ask questions – a good jeweller will spend some time with you and help you find a diamond you like that's in your price range.
  • Specifically ask if the diamond has been treated. The Gemological Institute of America (GIA) says a relatively small percentage of gem-quality diamonds are treated for two reasons: to improve clarity or to alter colour. But advanced treatment technologies are difficult to detect and require sophisticated instruments, so it's best to ask for a diamond that's been graded by GIA or another reputable lab such as Sydney's Gem Studies Laboratory (the Gemmological Association of Australia's endorsed diamond grading lab). It's worth knowing if the diamond has been treated as some treatments (colour coating) can wear off while others (laser drilling) can weaken the stone. Plus, treatments to turn a clear diamond into a 'fancy' colour may elevate the price and potentially be deceptive if not disclosed.
  • Examine the diamond in good light.
  • If you're looking for a diamond of 0.5 carat or more, ask for a grading certificate from an independent laboratory. A reputable jeweller sells stones with genuine Diamond Grading Reports or Certificates, says DCLA (Diamond Certification Laboratory of Australia).
  • Shop around – different stores sometimes price similar stones very differently.
  • Once you pay a deposit, ask for a detailed receipt describing the characteristics of the diamond and any associated piece of jewellery.
  • Get a valuation certificate from a valuer registered with the National Council of Jewellery Valuers. Valuations start from about $50, though some valuers charge a percentage rate attached to the final valuation price. Call ahead of time to agree on the cost.


There's a great deal of variation when it comes to the price of a diamond. How much your rock will cost you depends on the size, the cut, the origin of the diamond, whether or not it has any inclusions or irregularities, as well as a number of other factors. Do your research, shop around, and remember that if a deal seems too good to be true, it almost certainly is.

Dodgy diamonds

Take your business elsewhere if:

  • the salesperson tells you you're getting a huge discount on the stated value of the stone
  • their prices are just too cheap to be true, and no reliable certification is available
  • what's promised in advertising material isn't available in the shop.

The four Cs

You may have heard of the four Cs, especially if you've already started looking for an engagement ring. They're a set of criteria that help determine the value of a diamond and they include carat, cut, clarity and colour.


One carat equals 0.2g and is subdivided into 100 points. However, small weight differences undetectable to the eye (between 0.99 and 1 carat, or 0.74 and 0.75 carat, for example) can make a large difference to the stone's value. 

But weight isn't the only factor. A smaller high-quality diamond may be worth more than a larger one of lesser quality.


Diamonds are available in all kinds of cuts – brilliant (round), marquise (pointed oval) and princess (square) are just three possibilities, and refer to the shape that the raw diamond has been cut into. Look at examples and decide which you prefer, remembering that the better the standard of cut and quality of the finish, the better the brilliance and fire (brightness and sparkle) of the diamond.


Diamonds were formed millions of years ago through pressure and heat, so most contain imperfections or foreign material such as other stones or minerals called inclusions. A diamond's clarity grading tells you if inclusions are present. There are different grading systems, usually ranging from flawless (loupe-clear) to a small inclusion only seen through a 10x loupe (VS1), right through to those visible to the naked eye (I3 or P3)

Obviously, the fewer inclusions, the higher the grading and the more expensive the stone.


A perfect diamond is colourless, but most have a hint of yellow or even brown in them, which results in a lower grading ranging from D (exceptional white+) down to Z (tinted, usually yellow). However, very rare pink diamonds (mainly from the Argyle mine in Western Australia) and 'fancy coloured' diamonds, like canary yellow, can be very valuable.

Diamonds can be treated to improve their appearance. Treatments include artificial colouring, laser drilling to remove inclusions and fracture filling to conceal cracks. When a diamond is treated it's considered less rare and is viewed as an inferior product to a natural, untreated stone of similar specifications. Consequently, it's much less valuable.

Can man-made be as good as natural?

Synthetic diamonds (created in labs in a matter of weeks) and even imitation diamonds are readily available, and while some man-made stones are just as beautiful as naturally occurring diamonds, they're much less valuable than the real thing. The way to make sure you're getting what you paid for is certification – sometimes called the fifth C. A grading certificate from an independent laboratory exactly describes the characteristics of the stone.

There are independent Australian laboratories, some of them recognised by the World Jewellery Confederation (CIBJO), but the best-known labs are GIA in the US and HRD in Europe. In Australia, Gem Studies Laboratory (GSL) in Sydney is the Gemmological Association of Australia's endorsed diamond grading laboratory.

Certification is usually done before setting the stone, so if the diamond is already mounted, it'll need to be taken out before it can be certified.

Stock images: Getty, unless otherwise stated.