Engagement ring questions, answered by a diamond dealer

The “two or three months' salary” rule comes from an old De Beers advertising campaign. Today, the right budget is one that doesn't put you under strain. My advice as a diamond dealer: set an amount first, then look for the finest stone you can get within that budget. For the same money, a well-cut diamond that is slightly smaller will sparkle more than a large, poorly cut one. And keep part of the budget for the setting.

The price per carat jumps at the “magic” weights (0.50, 1.00, 1.50 ct). A 0.90 ct can cost noticeably less than a 1.00 ct, while the visual difference is minimal: roughly 6.2 mm in diameter versus 6.4 mm for a round brilliant. If the “1 carat” figure doesn't matter to you, the 0.90 ct is often the best choice. Otherwise, go for the 1.00 ct with a colour or clarity one grade lower.

On a slim finger (French size 48 to 50), a 0.50 to 0.70 ct diamond already looks generous. On a wider finger (French size 54 and up), the same stone looks smaller. The best thing is to try: I place several diamonds of different weights on the hand so you can compare. For American clients: a US size 5 is roughly a French size 49, and a US size 6 a French size 52.

Chemically, both are real diamonds. The difference: a natural diamond formed underground millions of years ago and is rare, while a lab-grown diamond is produced in a few weeks and its price falls every year. Choosing lab-grown is not “cheap” if it is a deliberate choice. I work with natural diamonds because they hold their value and carry a story. Personally, I love the story of a diamond born hundreds of kilometres underground, 1 to 2 billion years ago: that is the whole magic of a natural diamond. What matters is knowing what you are buying, and having it stated clearly on the invoice and the certificate.

To the naked eye, no. A lab-grown diamond and a natural diamond look identical; only laboratory equipment can tell them apart. That is why the certificate matters: it must clearly state “natural” or “laboratory-grown”, and the stone usually carries a laser inscription that can be read with a loupe.

A certified natural diamond can be resold, generally below the retail price you paid, but it keeps real value, especially if it is of good quality and GIA or HRD certified. A lab-grown diamond is very hard to resell, if at all, because its production cost keeps falling. Personally, I do not buy back lab-grown diamonds.

Cubic zirconia is an inexpensive synthetic stone (zirconium oxide): it sparkles at first, then scratches and turns dull over time. Moissanite is harder and very brilliant, with stronger rainbow flashes than a diamond. But its brilliance is so intense that it can sometimes look unnatural. Diamond is the hardest natural material: it keeps its sparkle for a lifetime and, when well cut, it truly blazes with light. For a ring worn every day, that makes a real difference.

For a natural diamond, the two benchmark laboratories are GIA (American) and HRD (Antwerp). Their colour and clarity grading is the strictest and most widely recognised, including on resale. NGTC is the Chinese national laboratory, used mainly in China. My advice: for a natural diamond, ask for a GIA or HRD certificate.

Every GIA or HRD certificate carries a number you can check yourself on the laboratory's website. This number is often laser-inscribed on the stone's girdle: you read it with a loupe or a microscope, and it must match the certificate. Be wary of “in-house” certificates issued by the seller: they are not independent.

Since 2003, the Kimberley Process has regulated the global trade in rough diamonds. But the safest guarantee is still a seller who knows the supply chain. I bought rough diamonds in Angola, the DRC, South Africa and on the Antwerp market for more than 20 years, and I regularly use traceability tools (Tracr, iTraceIt) and RJC certification for my clients. The most important thing is knowing who you are dealing with, and who the partners and suppliers are. I don't work with just anyone: only with members of the diamond trade and the diamond bourses. Always ask the seller what they know about the stone's origin.

An “eye-clean” diamond has no inclusions visible without a loupe at a normal viewing distance. In VS2, that is almost always the case. In SI1, it depends on each stone: some are flawless to the eye, others have a black inclusion right in the centre. You shouldn't buy a clarity grade on paper, you have to look at the stone, and that is what I do when I search for a stone for a client. A well-chosen SI1 can save you a lot.

On a ring, colour is easier to notice than small inclusions. Between G SI1 and H VS2, if the SI1 is eye-clean, I often go for the G SI1. On yellow gold, it's the other way round: you can go down in colour and keep a better clarity.

Yes, in fact it's a very good pairing. Yellow gold reflects into the stone: a J or K diamond looks whiter in it than in platinum, and costs noticeably less than a D, E or F diamond. It's a smart choice to get a bigger stone for the same budget.

Fluorescence is a glow, often blue, that appears under ultraviolet light. When faint or medium, it isn't visible in normal light, and on a slightly tinted diamond (I to K colours) it can even make the stone look a little whiter. When it is strong (Strong, or even Very Strong Blue) on a D to F colour, it can sometimes give a milky appearance: in that case, you need to see the stone before buying.

Almost all ovals have a darker area in the centre, shaped like a bow tie. The question is how pronounced it is, and it doesn't appear on the certificate: you have to look at the stone, in person or on video, from several angles. A well-cut oval has a light bow tie that moves with the light. I often compare several ovals to keep just one.

A natural coloured diamond is judged first on the intensity of its colour: Fancy Light, Fancy, Fancy Intense, then Fancy Vivid, the rarest. For a yellow, it is the strength of the colour that drives the price, far more than clarity. Insist on a GIA certificate stating “natural colour”. Some mines produce particularly intense and rare yellows, such as Zimmi in Sierra Leone.

Yes, and more and more couples choose one. Sapphire is almost as hard as diamond (9 out of 10): perfect for a ring worn every day. Ruby too. Emerald is more fragile: it needs a protective setting and a little care. For the same budget, a coloured gemstone often lets you have a bigger stone. Ask for a certificate from a recognised laboratory (GRS, SSEF, Gübelin, GIA, Carat Gem Lab, ALGT, Bellerophon, C. Dunaigre...) stating the origin and any treatments.

A few discreet tricks: borrow a ring she already wears, ideally on the same finger, and take it to a jeweller, who can measure the size in seconds (in a boutique or even in a shopping centre, it doesn't matter where). You can also trace the inside of the ring on a sheet of paper. If possible, ask her mother, her sister or a close friend. If in doubt, go slightly larger: it's easy to adjust, and the ring will slip on on the day of the proposal. With me, resizing and engraving are complimentary.

Yes, a gold or platinum ring can almost always be sized up or down by one or two sizes. It is trickier, or even virtually impossible, when the band is set with diamonds all the way round (full eternity band): the band sometimes has to be remade. With me, resizing is complimentary for my clients.

Both work, it really is 50/50. A complete surprise keeps all the magic, but you need to know her taste and her size well. The surprise is also the finished ring revealed as the box opens.

Antwerp is the world diamond capital, but that doesn't automatically make it cheaper for a private buyer: some shops mainly target tourists. What makes a good price is buying from someone with direct access to the diamond trade. I was born and raised in Antwerp. Quite naturally, I work with Antwerp, where I select stones and where some of my settings are made.

With a big brand, a large part of the price pays for the name, the boutique and the advertising. With an independent diamond dealer, you mainly pay for the stone and the craftsmanship. For the same quality, with the same GIA or HRD certificate, the gap can be significant. The right reflex: compare stones with the same type of certificate, not just brands.

Buying online can work if you know how to read a certificate. But two stones with the same certificate can look very different: brilliance, visible inclusions, tint. My clients trust me for my experience and because I always look for the best option. You need to see the stone in person, or at least on video: I always send several videos so the diamond I'm selling is properly understood. That is how I avoid unpleasant surprises.

It depends on the country and the timing. For visitors who live outside the European Union, the 20% French VAT can generally be refunded through tax-free shopping, which makes buying in Paris attractive. But you have to factor in customs duties when you return home. I also offer tax-free shopping (VAT refund).

Each country has its own rules: duty-free allowance, rates, declaration. For example, South Korea applies an $800 duty-free allowance, and the UAE requires jewellery above AED 60,000 to be declared. Always keep the itemised invoice and the certificate with you. For an exact calculation, check with your country's customs before you travel.

Always keep it in your cabin baggage, with the invoice, and insure it before you leave. So that she doesn't discover it at airport security, some people hand it to a friend or relative. The simplest solution: buy or collect the ring in Paris, the day before the proposal. I also sometimes keep the ring until the day of the proposal.

At sunrise, the Trocadéro or the Bir-Hakeim bridge give you the Eiffel Tower while it is still quiet. For more privacy: the Palais-Royal gardens, the Bagatelle rose garden in spring, or a private cruise on the Seine at sunset. Many couples bring in a discreet photographer to capture the moment.

Yes. I start with a 3D design of the ring, which you approve before production. You can still adjust the height of the stone, the thickness of the band or the shape of the prongs. The ring is then made in 18-carat gold or platinum, in Paris or Antwerp. It usually takes about 2 weeks after the design is approved.

An appraisal is a document that describes the ring and states its replacement value: it is what the insurer asks for. You can add the ring to your home insurance (check the limit for jewellery) or take out specialist jewellery insurance. Keep the invoice, the certificate and photos of the ring.

Yes, a well-made ring can be worn every day. Take it off for sport, gardening or household cleaning products. Have the prongs checked once a year: a worn prong can let the stone fall out. White gold is plated with rhodium, which wears off over time: re-plating restores its whiteness. To clean it: warm water, mild soap and a soft brush. Otherwise, my clients drop by for a quick ultrasonic bath: the time for a short stroll, and the ring is clean.

In France, the engagement ring is worn on the left ring finger, then together with the wedding band on the same finger. In Germany, the Netherlands or Russia, the wedding band is often worn on the right. To match the two well, think about it from the start: the setting can be designed so the wedding band sits flush against it with no gap.

Platinum is the most classic option: white, heavy and very strong. Palladium, from the same family, is lighter and less expensive. Silver is possible but scratches more quickly. I make wedding bands in platinum and sometimes in palladium.