Flashes of light bouncing off spangles that appear to be floating inside the dial: an optical effect known as aventurescence that can be appreciated on many luxury watches, against a backdrop of green at Bovet Fleurier for the Rising Star or red-brown at Jaeger-LeCoultre and its Rendez-Vous Moon Aventurine Ochre. Many watchmakers – Jaquet Droz, Girard-Perregaux, Bulgari, Van Cleef & Arpels, Chanel – prefer blue, sometimes so deep as to be almost black. But is this aventurine the same as the orange-red variety of the Tonda 1950 Poppy Aventurine by Parmigiani Fleurier?
Indeed, all “aventurines” share this same sparkling magic but some are the work of nature while others are man-made. Most of the aventurine used in watchmaking is a synthetic form known as aventurine glass, although confusion does still arise and understandably so, as we shall see.
The many facets of aventurine
There are three, even four types of “aventurine”. First, aventurine feldspar and aventurine quartz, both gemstones. Then aventurine glass. And last of all a lacquered imitation. Just to complicate matters further, aventurine feldspar is also called sunstone while aventurine glass goes by the name goldstone. Stone me! And that’s not all: green aventurine quartz can also (sometimes with a few illicit tweaks!) pass for Indian jade.
And yet the official terminology is clear as glass. “If it is a ‘glass’ imitation of quartz or feldspar aventurine, the product must be described as ‘imitation aventurine’ or ‘simulant aventurine’. The term ‘glass’ may also be used. ‘Aventurine’ must never be used to describe an imitation,” says Roland Naftule, President of the World Jewellery Confederation (CIBJO) Sector A, which deals with gem material.
What's in a name?
This terminological mashup has its roots in history. In the eighteenth century, a Venetian glassmaker accidentally spilled copper filings into molten glass, inadvertently inventing aventurine glass. He named his discovery “aventurine” as it had come about “per avventura”, i.e. by chance. So the story goes: in reality, as The Oxford Companion to the Decorative Arts tells us, the Ancient Egyptians already mastered production of aventurine glass (and other forms of glass). Subsequently, the technique was lost then revived several times over the course of the centuries. Some (Max Bauer, Precious Stones; Robert Webster, Gems and Gemology) claim there never was any butterfingered glassmaker; the story was invented to keep the actual formulation a closely guarded secret. Others attribute the name to Salviati, a Murano glassmaker who, in the second half of the eighteenth century, became the first to achieve the almost impossible feat of blowing aventurine glass.
Come the nineteenth century, the word “aventurine” was applied to a newly discovered variety of quartz with gold-coloured inclusions. “This must be about the only instance when jewellers have applied the name of a cheap artificial product to a better natural stone,” notes the Jewelers’ Dictionary (3rd edition, Donald S. McNeil). And so “aventurine” is now commonly used, including among watchmakers, to refer not just to the glass but also to the stone.
Proper use of terminology is nonetheless vital in product descriptions: “The raw material has a higher cost when it’s the natural version,” explains Catherine de Vincenti, founder of CdV Consulting and founder member of the Swiss Gemmological Group. Dona Dirlam, director of the Gemological Institute of America (GIA) library, notes that “aventurine quartz and aventurine feldspar would be more durable than aventurine glass.”
From an aesthetic point of view, watchmakers nonetheless prefer aventurine glass for its transparency and more regular aspect. From a technical perspective, both glass and stone are difficult to prepare and assemble, due to the thinness required for a watch dial, and in certain instances the desired form. Bulgari, which manufactures its dials in-house, emphasises the dexterity required to assemble the Giardino Notturno watch, and the attendant labour costs.
The raw material is sourced almost exclusively in Murano, where production is virtually at an end. It involves the use of harmful substances which have now been banned.
For these reasons, authentic aventurine stone is a rarity in watchmaking. The Tonda 1950 Rose Gold Set Poppy Aventurine by Parmigiani Fleurier offers one of the few examples to admire its natural scintillation. The red-orange of the quartz is made more intense by the application of a poppy-red lacquer.
What if aventurine glass were to become just as rare? The raw material is sourced almost exclusively in Murano, where production is virtually at an end. As well as being time-consuming and labour-intensive, it also involves the use of harmful substances which have now been banned. A lesser quality glass is manufactured in China and India but is unsuited to high-end watches. Suppliers, such as Daniel Haas in Switzerland and Groh & Ripp in Germany, therefore tap into stocks that were built up in the past. To top it all, each batch of glass is subjected to a stringent selection process, resulting in a lot of waste, to obtain uniform colour and sparkle with no air bubbles. Fortunately, several tons of aventurine glass have been stockpiled in Murano; more than enough to produce any number of magnificent dials. By which time watchmakers could be showing more of an interest in genuine aventurine…