Aventurine is a name used for variations of the minerals quartz and feldspar. More frequently, it is also used to refer to a type of glass said to have been created by chance.
The story goes that a Venetian artisan mistakenly mixed copper shavings into molten glass, producing what a German diplomat described in a 1614 letter as “a sort of stone with golden stars inside.” Julie Bellemare, curator of early modern glass at the Corning Museum of Glass in upstate New York, said in a telephone interview that the letter may be the earliest reference to aventurine glass.
In recent years, the popularity of aventurine — both the mineral and glass versions — has soared among horological brands and watch collectors alike. A. Lange & Söhne and Czapek & Cie have used aventurine glass dials to evoke a midnight sky of twinkling stars or the mysteries of the cosmos. Omega has used the mineral versions as well as the glass version.
“No dial is equal, no dial is the same,” said Anthony de Haas, director of product development at A. Lange & Söhne, “but it is always elegant.”
Throughout the 17th and 18th centuries, according to Dr. Bellemare, the basic ingredients for aventurine — plant ash and silica from sand or quartz pebbles, along with copper — were mixed into clay crucibles and fired in large blocks.
“It was a completely different process than glass blowing,” she said. “The blocks were a square foot, sizable and you didn’t know at the end of the firing if you would get what you were expecting.” The recipe was a closely guarded secret and most likely changed in the 19th century, Dr. Bellemare said, and when it changed, so did the production method.
Mr. de Haas, describing how “glass with thousands of pieces of copper” is produced today for A. Lange & Söhne, said the glass is melted and the pigmentation chosen. The glass blowers “let it grow like a carrot” and flakes of copper are dropped in, he said. “It hardens and then they cut the carrot in tiny slices.”
The company’s dark blue glass is then made into dials in Germany, then shipped to Switzerland to be polished.
Mr. de Haas said the brand introduced copper-blue, its take on aventurine, about five years ago. “People went nuts,” he said in a video call. “It was the first fancy color thing we did at Lange, and the first time a brand used that material in that price range.”
When the Saxonia Thin, a 39-millimeter timepiece with an 18-karat white gold case and a copper-blue dial, was introduced in January 2018, it retailed for $22,000. The current price is $29,000. Since then, the company has used the material for watches in the Lange 1 Family line, including the Little Lange 1 Moon Phase.
“This midnight blue is genderless but delicate,” Guillaume Chautru, head of gemology at Piaget, said in a video call. “It is a high-level color, chic, that can be loved by anybody.”
Long known for its use of minerals and stones for dials, Piaget transitioned within the past few years to using aventurine glass in place of the lapis lazuli it can no longer acquire from Afghanistan.
“Once the glassmaker figured out how to homogenize the color with the same amount of copper oxide, we knew it was a Piaget color,” Mr. Chautru said.
Achieving the 0.4 millimeter thinness required for Piaget’s dials, always difficult, is easier with glass than with natural stone, he said. Piaget now has seven references with dials of blue aventurine glass, in prices ranging from $27,200 for a Limelight Gala watch to $146,000 for an Altiplano Tourbillion.
A request from a collector inspired the Swiss independent brand Czapek & Cie’s recent foray into aventurine glass.
“An aventurine dial changes your watch totally; the effects of the pieces of metal shining and reflecting is really mesmerizing,” Xavier de Roquemaurel, chief executive of Czapek, said in a video call.
“And then we have our collectors; they ask for aventurine by name.”
A year ago, an Italian collector commissioned the Antarctique Aventurine, which featured baguette-diamond indexes Mr. de Roquemaurel said he was happy to oblige, although working with aventurine glass is difficult.
When you have a complex design, he said, “or applied indexes, there’s all the risks, and you’re likely breaking one out of three or four dials in the process. The dial maker is not the aventurine maker, and while the initial material is not very expensive, you have to do a minimum number.”
The Italian collector’s commission has since led to the creation of an 18-piece limited-edition collection, each $45,000 and timed for release around the year-end holidays.
Omega uses aventurine in both the glass and minerals’ stone forms. “The gap between the natural stone that is unique and comes from the earth and the glass that is produced by a machine in an industrial way is quite big,” said Gregory Kissling, vice president of product at Omega, referring to differences in the natural stone and the manufactured product.
Omega started to use the glass in 2013, and it is now used in the dials of 21 of the brand’s watches, including several 29-millimeter Constellation references.
The brand’s patented glass process involves crushing aventurine glass to a powder and then using it in an enamel, said Gregory Kissling, vice president of product at Omega. While the end result, used in the brand’s De Ville Trésor collection, looks like classic aventurine glass, there is less breakage in the enamel version — two or three dials are broken for each one that ends up in a watch. But, “that is the nature of these materials,” Mr. Kissling said in a video interview.
Omega began using aventurine quartz in 2021, buying supplies from India and Brazil, although it can also be found in Russia, Tanzania and the United States.
And while the quartz version can range in color from a deep reddish-brown to blues and greens, Mr. Kissling said it was more sellable in blue. “Blue is the new black in the watch industry,” he said.
To use aventurine quartz, Omega created what it described as a new dial construction method. A brass base with a proprietary inlay and shape is constructed and then the mineral is affixed to it. The base, Mr. Kissling said, would absorb the shock if the watch were dropped or banged, preventing the mineral from cracking or breaking.
Mr. Kissling said both versions of aventurine have proved popular.
“It’s the universe, the stars and emotion,” he said. “Every time we present it, there is always a wow effect.”