Aventurine ('avventurina' in Italian) is a specialised glass invented in 17th-century Murano. The recipe doped molten silica with copper or chromium flakes; the metal precipitates within the glass as fine crystals that scatter light, producing the characteristic starfield sparkle. Most aventurine watch dials are deep blue with copper flakes, evoking a night sky; less commonly green (with chromium) or red.
Aventurine dials are mostly used on dressy or astronomically-complicated references: moonphase, world-time, perpetual calendar, celestial complications. The dial itself is decorative rather than functional (the printed/applied indices and hands sit on top of the aventurine), so brands use it where the dial is the star of the show. Common in JLC Reverso 'starfield' dial editions, Patek 5396 limited variants, and Vacheron Métiers d'Art.
