Buying a diamond involves more decisions than buying bullion, and unlike bullion there is no spot price to check. Two stones of the same carat weight can differ in price several times over, and without knowing what drives that you cannot tell a good buy from a poor one.
Here is the order the decisions actually matter in.
Step one: decide lab grown or natural
This is the first fork and it changes everything downstream, particularly budget.
Lab grown and natural diamonds are the same material, with identical hardness, appearance and optical properties. No jeweller can tell them apart by eye. What differs is that lab grown stones currently sell for roughly 80 percent less than comparable natural ones.
That means the same money buys a substantially larger or higher graded lab grown stone. It also means lab grown prices have fallen sharply and continue to fall, and resale returns a small fraction of purchase price.
Our full comparison is in lab grown or natural diamonds. The short version: buy either to wear and keep, and neither with resale in mind.
Step two: set the priority order
The four grading characteristics are not equally important, and knowing the order is where most of the value in a budget sits.
Cut first. Cut determines how the stone returns light. A poorly cut diamond looks dull no matter how good its other grades are, and a well cut stone at lower colour and clarity will outshine it.
Then carat, buying just under a round number. Price jumps at round weights, so a 0.95ct stone costs noticeably less than a 1.00ct one and looks essentially identical.
Then colour, in the near colourless range. G through J appear white to most eyes once set, at meaningfully less than D through F.
Then clarity, buying eye clean. Clarity is graded under 10x magnification. If inclusions are invisible to the unaided eye, paying for a higher grade buys nothing you will ever see.
The detail is in the 4Cs explained.
Step three: choose a shape
Shape is the genuinely personal decision, and it affects price and apparent size.
Round brilliants cost the most per carat because cutting one wastes the most rough. Elongated shapes such as oval and pear look larger for the same weight. Step cuts such as emerald and Asscher need higher clarity, because their large open facets show inclusions that a brilliant cut would hide.
More in diamond shapes explained.
Step four: insist on certification
This is the one step with no flexibility in it.
Without an independent grading report, terms like colourless and eye clean are the seller's opinion, and prices between sellers cannot be compared at all. A report from a recognised laboratory states the measured grades, whether the stone is natural or laboratory grown, and whether any treatment has been applied.
Check the report yourself using the laboratory's online verification tool, and check that the laser inscription on the girdle matches the report number. It takes a minute and almost nobody does it.
Note also that a certificate is not an appraisal. An appraisal estimates retail replacement value for insurance and is not independent grading. See diamond certification explained.
Step five: see it in person if you can
Two stones with identical paperwork can look different. Grades describe measurable characteristics, not the overall impression a stone makes, and things like a bow tie in an elongated shape or the effect of fluorescence do not always show on a report.
If a purchase is significant, viewing the stone is worth the trip.
What about coloured stones
Fancy coloured diamonds work differently. They sit outside the colourless grading scale, colour intensity dominates value, clarity matters much less, and cut is optimised to present colour rather than brilliance. See fancy coloured diamonds explained.
Frequently asked questions
How do I start buying a diamond in New Zealand?
Decide between lab grown and natural, prioritise cut over the other grades, choose a shape, and buy only certified stones you can verify.
Should I buy lab grown or natural?
Lab grown gives far more size and quality per dollar. Natural has better secondary market support. Neither should be bought expecting to recover the purchase price.
Which of the 4Cs should I prioritise?
Cut, because it determines how the stone actually looks. Then carat just under a round number, then colour in the near colourless range, then the lowest eye clean clarity.
Do I need a certificate?
Yes. Without one, the grades cannot be verified and prices cannot be compared.
Can I see diamonds in person in Christchurch?
Yes. Our showroom is at 124 Peterborough Street, Christchurch.
Our diamonds
We hold certified lab grown and natural stones, including a 5.03ct lab grown round brilliant, a 1.06ct fancy vivid pink, and a 2.00ct natural round brilliant. See the range or visit the showroom at 124 Peterborough Street, Christchurch.
This article is general information about buying diamonds and is not financial advice.