The largest of the marble seashells are more than 4 feet in length and can weigh close to a ton. They are titans compared to the homes of the marine mollusks they are modeled on, but in photographs, they could easily be mistaken for the real thing. Part artistic sculptures and part faithful replicas, they are the meticulous result of a husband-and-wife team producing objects of astonishing beauty and originality.

“My wife, Raffaella, and I met when we were students at Pisa University,” says 70-year-old Roberto Quai. “She was studying natural sciences, and I was studying geology, so you could say we’re ideally qualified to carve shells out of stone.”

Of mixed Italian and Ethiopian descent, Quai has marble dust in his veins. His father operated several quarries in the former Italian colony of Eritrea. Today, Quai runs his own company, Stone Consulting and Contracting, which specializes in the supply and installation of all manner of structural and decorative stone for luxury residences, public buildings and superyachts.

The company has completed commissions in 44 countries and worked on more than 30 superyachts, including the 344-foot (105-meter) Lady Moura, launched by Blohm+Voss in 1990, and the 347-foot (106-meter) converted passenger vessel Dream, completed in 2018.

Several of the yacht projects feature bespoke mosaics, often based on sea creatures, created from hand-carved stone tiles that Quai was contracted to design and install. The idea for the marble shell sculptures came when the couple was searching for new product ideas.

“The light-bulb moment was when an American architect working in Italy saw a small marble shell that I’d made,” he says. “It was only about a foot long, and he suggested making much bigger sculptural versions, and we’ve sold more than 50 of them to date. Most have ended up in private residences where they’re usually used as ornaments for gardens and swimming pools.”

Quai no longer works the stone himself, but his workshop is based in Pietrasanta, close to the marble quarries of Carrara in Tuscany where Michelangelo sourced the marble for his statue David. All the shells are based on real-life species, and sometimes a scale model is made before tackling the actual sculpture.

The first stage in the production process is to select the variety of marble that best suits each specimen. The Conus shells, for example, are mostly fashioned from calacatta oro or breccia violetta marble with dramatic veining that echoes the patterns of the shells in nature, whereas the Lambis shells are made from rose Portugal marble that has a delicate pink or orange hue uncannily close to a real conch.

The next stage is to cut and chip away at the marble block, first with power tools and then with a hammer and chisel, to create a shape that approximates the final product. The trickiest phase requiring the skilled hand of an artisan is fashioning the whorls, spires and spindles that characterize the different shells. The Lambis shell, for example, has a flared outer lip with hollowed-out marginal digitations that can easily break off under a careless hammer blow.

The final process is adding the rough striations to the outer surface of some shells, and polishing the smooth inner surface deep inside the aperture (or “undercut” in stone masonry) where the gastropod actually lives in nature—a job that requires both an eye for detail and plenty of elbow grease. From beginning to end, the whole process can take a month.

Marble might seem a ponderous medium for creating something as delicate—but not necessarily fragile—as a seashell. But the two materials have more in common than you might think, as both are made of calcium carbonate. In the case of seashells, the animals inside them extract the dissolved calcium and bicarbonate from the marine environment.

Marble is a metamorphic rock of carbonate minerals formed when chalk or limestone is recrystallized under high temperature and pressure. The low refractive index of calcite means that light can penetrate quite far into the stone before it is scattered, lending marble sculptures their lifelike luster. In fact, when viewed in the right light, the thinner parts of the marble shells are almost translucent, just like shells on the seabed.

Antonio notes that the skilled artisans who produce these sculptures are a fast-disappearing breed.

“There’s no doubt the craftsmanship is dying out,” he says. “It’s hard, dusty work, and young people don’t want to do it. It’s getting increasingly difficult to find the people able to work the stone and achieve the kind of high-quality, creative results our clients expect.”

This article was originally published in the Spring 2021 issue.