or a long time Guillaume Chautru worked away from the spotlight… nothing unusual for someone whose job it is to procure precious stones for a foremost jewellery house. Prior to taking over at the head of Piaget’s gemmology department six years ago, his previous role was at Cartier. And long before that he was a snake breeder. Reptiles are still one of his passions, along with diving and colour change gems.

I caught up with Guillaume Chautru during Watches & Wonders in Geneva last April. One of the display cases contained a stunning necklace, designed to be worn in nine different ways, set with a yellow diamond and a magnificent spinel. Only in recent years have spinels started to interest collectors, pushing up prices significantly. Both these stones have a story that Guillaume Chautru was only too happy to share.

Guillaume Chautru, head of the gemmology department at Piaget

In July Piaget presented its Solstice high jewellery collection. Each piece is set with a magnificent centre stone, such as a 15.02-carat Sri Lankan sapphire among an eruption of diamonds, a 9.10-carat emerald from Zambia on a lacelike necklace, and a 6.06-carat Madagascan pink sapphire surrounded by diamonds. All these stones were sourced by Guillaume Chautru.

Europa Star: Would it be correct to say you’re a treasure hunter?

Guillaume Chautru: You could say that. I go looking for rare stones. All the more rare because there is a lot of competition for a non-renewable supply. At the same time, demand for the highest quality stones is increasing. Customers no longer accept inclusions in coloured stones, for example. This means we have to recut around 90 per cent of all the stones we find.

A precious stones broker (read here) told us that only 2 to 3 per cent of stones are of investment quality. Do you agree?

Yes and probably less than that when you take liquidity into account, which not everyone does. A large stone is very difficult to sell.

“Not everyone takes liquidity into account when considering stones as an investment. A large stone is difficult to sell.”

Setting the Flamboyant Nightfall necklace with a rare, 15.02-carat sapphire from Sri Lanka

When sourcing centre stones for Piaget jewellery, do you look primarily for investment stones?

Our Trésor range is composed solely of so-called investment stones, but this isn’t our main motivation. We look for the most beautiful stones possible in terms of colour and clarity, with the best possible cut. Our quality criteria are so high that any stone we purchase automatically becomes an investment stone.

What job did you want to do when you were growing up?

I can’t remember, but my first job was breeding snakes. I started when I was fifteen and continued for almost ten years. I used to select the male and female specifically so that they would produce very colourful young. My three passions in life are scuba diving – I love swimming among corals and fish – reptiles and gems. And colour is the one thing they have in common. So you could say I’m passionate about colour.

Guillaume Chautru’s passion for reptiles, the underwater world and colour change gems have colour as their common denominator.

Gouache for the Flamboyant Nightfall necklace

Does this influence which stones you select?

It does, although I choose stones not to suit my own taste but because they correspond to the identity of the brand that employs me. Fortunately Piaget is known for its colourful, flamboyant designs.

Do you ever buy for yourself?

I used to, a lot, when I worked freelance, but always as gifts. I recut them and gave them as gifts.

How did you move from snakes to gemmology?

I used to go looking for snakes in places, mainly around Southeast Asia, where there were mines. I met a lot of the people working in these mines and they introduced me to the business. I spent time with stone cutters in Sri Lanka and Burma, and really wanted to learn for myself. After that I studied gemmology and learned how to cut stones. I taught, too. So it’s really thanks to people that I became involved with stones.

“I used to go looking for snakes in places, mainly around Southeast Asia, where there were mines. I met a lot of the people working in these mines and they introduced me to the business.”

Any favourite stones?

I have a soft spot for pink sapphires, which are the most powerful stones I know. Padparadscha for the blend of tones and also colour change sapphires.

The Extraordinary Lights Necklace from Piaget’s Limelight high jewellery collection can be worn as eight different necklaces and as a bracelet. It is set with an 8.88-carat, cushion-cut, fancy vivid yellow, IF diamond centre stone, a 5.34-carat, pear-cut sapphire from Sri Lanka and a rare 3.61-carat Tanzanian spinel.

The yellow diamond centre stone of the necklace displayed at Watches & Wonders is truly beautiful. There is also an unusually coloured spinel. What’s the story behind them?

When we create a set composed of a necklace, a ring and earrings, I start with the centre stone for the necklace. We begin with the most complicated stone [to source] so we can then be certain of matching the other stones with it. I found a yellow diamond of just over 9 carats, but it didn’t meet my criteria because of a small inclusion in the pavilion. However, once I’d calculated the angles to recut it and increase its colour density, I realised that would get rid of the inclusion. Piaget and the Richemont group trusted my judgement, although I did have to convince certain cutters who thought it was fine as it was. We succeeded in transforming a 9.05-carat diamond into an 8.88-carat, internally flawless fancy vivid yellow. By shaving off half a carat and getting rid of the inclusion, we added 30 per cent to its value!

What about the spinel?

Piaget only works with one type of Tanzanian spinel, from a small mine that produced stones during one single week, twenty years ago. The last word in quality! They’re easily recognisable: the crystal is extremely clean and the finest red colour. Sourcing them means first finding out who had the roughs when they were mined, then seeing who owns them today and whether they want to sell. Most of the time these are rough stones, which is an advantage for us as we can cut them to our specifications. Every spinel that Piaget buys comes from that mine, which is why we have so few.

”Piaget only works with one type of Tanzanian spinel, from a small mine that produced stones during one single week, twenty years ago. The last word in quality!”

Why do you think the spinel is such an underappreciated stone? After all, there is a spinel mounted in the British Imperial State Crown, despite being known as the Black Prince’s Ruby.

It’s a matter of time. The spinel is a noble material with a hardness of 8, hence sufficiently hard to be used in jewellery [diamond has a hardness of 10, sapphire and ruby 9, emerald between 7.5 and 8]. Spinel is magnesium oxide whereas ruby is aluminium oxide. Its refractive index is close to that of ruby. The Black Prince’s spinel was thought to be a ruby for so long because both stones occur in the same deposits and they share similar physical and chemical properties. Spinels have increased in value as customers have become more familiar with them and learned to appreciate this stone. Prices have rocketed over the past ten years.

What comes first, the drawing or the stone?

Around 80 per cent of collections are designed around the stones. This enables us to bring out new pieces at a fairly steady rate. Once we’ve sourced the stones, we’ve done the hard part.

Precious Adornment Necklace. The 9.21-carat, emerald-cut, no oil emerald from Zambia was cut by Piaget from a 16-carat stone with multiple inclusions.

Tell us about your best ever discovery.

A 16-carat emerald with very little oil that was full of inclusions, which I recut last year. When I bought it, my team were convinced I must have had too much to drink (laughs). The beautiful crystal inside certainly wasn’t easy to see. It was recut seven times over three years and went from 16 carats to a 9-carat emerald with no oil and no inclusions. It’s now worth five times what I paid for it. I’m fortunate that Piaget leaves me to do my job, considering how long it took and the risks involved: emerald is easily broken. But it was certainly worth it. For the end customer, this is a fabulous opportunity. In fact it’s in the process of being sold. Going forward, it will be impossible to entirely satisfy a customer who has very exacting criteria without making significant recuts.

“The 16-carat emerald I recut last year is now a 9-carat emerald with no oil and no inclusions. It’s worth five times what I paid for it.”

How did you spot the pure stone among all those inclusions?

I always work with a lamp and inspect the stone along very specific axes. The problem with emeralds is that the inclusions are along three directions, which you have to bear in mind when picturing the cut stone. It’s a slow process and it all comes down to experience. As we say in the business, “I’ve eaten plenty of roughs” in my lifetime.

In your line of business, there’s always the risk of making a mistake. Has that ever happened?

When I was teaching, I always told my students it takes ten years to make a name as an expert and ten seconds to lose it. A few years ago I was looking for stones in Chanthaburi, in southern Thailand. It was the end of the day and nothing really worthwhile had come up when suddenly I was handed a bag full of violet spinels, all mediocre quality. I didn’t have any colour change spinels in my collection, so I thought why not see if there is one? I inspected every stone in the bag using a special lamp and came across a 5-carat spinel with the most magnificent colour change.

The gentleman wanted to sell the whole bag but I was only interested in that one stone. In the end he agreed. Back home I showed it to a friend who congratulated me on “an amazing Burmese sapphire”. I was convinced I’d bought a spinel but when I looked at it with my binocular, I saw that it was indeed a sapphire. The thing that fooled me were the octahedral inclusions, which are characteristic of spinels, but Burmese and occasionally Sri Lankan sapphires can have them, too. And that’s how I came to pay $50 for a magnificent, 5-carat, Burmese colour change sapphire. Not a bad mistake to make!

Voluptuous Ribbon Necklace, set with a 6.06-carat, cushion-cut, unheated pink sapphire from Madagascar

What about your biggest disappointment? A stone you weren’t able to buy, for example?

I remember a 9-carat, pear-shaped ruby. Not something you see every day. It had an elongated form and I wanted to cut it into a shorter, 8.88-carat stone, which would have cost a lot to do. The marketing department said no. The person who did buy it turned it into the most incredible stone and it’s now worth double what it cost.

Why 8.88 carats?

Because eight is a lucky number in Asia. Whenever I’m cutting a stone and I get close to 8.88 carats, I always try and hit the mark, as this will give the customer an additional reason to buy. I tell myself it will be lucky for me, too. At the Piaget boutique in Macau there are 7.77-carat diamonds for customers who want to try their luck at the casino.

If you could have any stone at all, what would it be?

I’m mad about colour change garnets. There is a mine in Bekily, in southern Madagascar, that is the only one in the world to have produced blue garnets [in the 1990s]. This is a very masculine stone that changes from a deep Kashmir blue to almost the same red as a Burmese ruby. The mine no longer produces them. It’s my dream to one day find one.

“There is a mine in southern Madagascar that is the only one ever to have produced blue garnets. It’s my dream to one day find one.”