A guide to choosing the right engagement ring

It is by far the most common, and the most logical: you spot a ring online, fall in love with its design, and then look for the gemstone that will fit it.

The problem is arithmetic. A design fixes dimensions; you must then find a stone that matches that exact format, in that colour, within that budget — three simultaneous constraints. Nine times out of ten, you end up accepting a gemstone chosen by default.

The reverse order costs less and produces a better result: you choose the stone from what actually exists, then the setting is designed around its dimensions. In this respect, a sapphire engagement ring offers the widest scope — ten colours and the deepest stock in our catalogue, hence the fewest compromises to make.

The carat measures weight, not a cut. Two stones of the same weight can differ by more than one millimetre in diameter depending on their cutting depth — and many are cut deep precisely to retain carat weight, and therefore sell for more despite having the same visible surface area.

The case of red is the most striking, and it should be a lesson to everyone. Among our six rubies in stock, the price per carat decreases as the weight increases : the smallest stone, a pure red 1.50 ct ruby, costs €22,520/ct, while the largest, pinkish in tone, falls to €5,800/ct. A ruby engagement ring should therefore be judged by its saturation, never by the number on the certificate.

A practical consequence, valid across all families: be wary of a large stone offered at a price that seems reasonable. Nine times out of ten, it is not a bargain — it is a more subdued colour, heavy treatment, or both.

A stone does not create light: it reflects what it is given. Warm light draws tones towards red, daylight towards blue. The same teal sapphire may appear distinctly blue in a display window and noticeably green by the window.

No screen is calibrated like yours, and a studio photograph is lit to flatter. The test that matters lies elsewhere: view the stone in daylight, then in the evening in a lit room. If the colour collapses when the light fades, the ring will not leave the drawer.

At a distance, the minimum acceptable option is a video on a neutral hand, under several lighting conditions, without colour retouching. A seller who provides only retouched photographs is selling you an image, not a gemstone.

This cannot be remedied later. A wedding band sits against the engagement ring — and this question alone changes three design parameters that can no longer be altered once the ring has been made.

The three parameters are the setting height — a low-set stone will never allow a straight band to sit flush —, the profile of the band, and the shape of the basket beneath the stone, which may protrude and prevent any contact.

On an emerald engagement ring, the issue goes beyond aesthetics. With a hardness of 7.5 to 8, the stone does not withstand repeated friction from metal against its edges well: we almost always design a notched wedding band, even when the geometry would allow a straight band.

The most reliable method remains discreetly borrowing a ring she wears on her left ring finger and having it measured. Two pitfalls account for most mistakes.

The wrong finger. A ring worn on the middle finger or right ring finger does not provide the correct measurement: the difference often reaches one and a half sizes. For right-handed people, the right ring finger is frequently half a size to one size larger than the left.

The wrong time. A finger measured in the morning, after sport or in hot weather can vary by a full size. Measure at the end of the day, at normal temperature.

An independent laboratory report, verifiable by its number, specifies the nature of the gemstone, its weight, dimensions, any treatments it has undergone and often its origin. Without it, no price makes sense.

The first line to read is that concerning treatments, because they determine both value and care. Heating a corundum and oiling an emerald are traditional, stable and accepted. Lead-glass filling in a ruby, coloured resins in an emerald or surface diffusion, on the other hand, are not: they drastically reduce value and weaken the stone.

A useful point for inherited jewellery: discovering that a family stone is treated or synthetic does not mean you have been deceived. Ruby has been synthesised industrially since the beginning of the 20th^th century, and no one concealed it at the time.

Allow six to eight weeks between the first appointment and the handover of the jewel: one to two weeks to choose the stone and finalise the design, followed by three to five working weeks of production once the stone has been received at the workshop.

The final line deserves a word, because it is the escape route no one considers. Proposing with the stone alone, in its presentation case and with its certificate, then designing the ring together: the commitment is there, as is the value, and it removes the main risk of a surprise ring — getting the design wrong rather than the stone.