Rock crystal, the eternal ice of the ancients

Rock crystal is the purest and most transparent form of quartz. Its clarity, which makes it look like solidified water, has struck the imagination of every age, and the word crystal itself comes from the Greek krystallos, which originally meant ice. From Roman antiquity to the Christian Middle Ages, from the Fatimid courts to Renaissance collections, this mineral has been used for precious objects, reliquaries and amulets, always associated with purity and vision.

Pliny's petrified ice

Pliny the Elder, in the thirty-seventh book of the Natural History, reports the opinion that crystal forms from ice hardened by intense cold, and notes that it is found in the Alps, in places where the winter snows freeze most deeply. The idea, which went back to the Greeks, would last for centuries. Pliny adds that physicians regarded crystal spheres, exposed to the rays of the sun, as the best means of cauterising.

Crystal was also a luxury fit for emperors. Pliny himself relates that Nero, on learning that all was lost, smashed two crystal cups in a fit of rage, to punish his age by preventing anyone else from drinking from them. The anecdote says a great deal about the value Rome placed on these objects. Pliny also records that a matron, not especially wealthy, had paid one hundred and fifty thousand sesterces for a single crystal cup.

Spheres and reliquaries

In Frankish and Alamannic women's graves of the fifth to seventh centuries small spheres of rock crystal are often found, enclosed in a metal mount and hung from the belt. Their precise use is not described by any written source, but the context and the frequency of the finds suggest protective or propitiatory objects, carried throughout life and finally laid beside the dead woman.

In the Christian Middle Ages crystal became the ideal material for reliquaries, because it allowed the relic to be seen while keeping it protected. The so-called Lothair Crystal, engraved in the Carolingian period with the story of Susanna and now in the British Museum, and the Fatimid ewers in the Treasury of San Marco in Venice, one of which bears the name of the caliph al-Aziz, show the refinement its working attained.

The stone of vision

The transparency of crystal soon linked it to the idea of vision. In the Renaissance some figures of magical culture, such as the English mathematician and astrologer John Dee, adviser to Queen Elizabeth I, used polished, transparent stones as instruments for receiving visions. The British Museum holds a crystal ball traditionally associated with Dee, alongside an obsidian mirror of Aztec origin also attributed to him.

Eternal ice for the Romans, a window onto the sacred for Christians, an instrument of vision for Renaissance magicians: rock crystal changed its meaning without ever losing its bond with purity and light. The virtues attributed to it belong to the history of beliefs, but the objects born from it, from imperial cups to medieval reliquaries, are among the most fascinating works of the luxury arts.