Roman glass theory wrong for centuries

Roman art historians are unanimous in the opinion that a cameo glass known as the Portland Vase, thought to date from between 1 and 25 CE, is pretty much the best piece of ceramics to have survived the past two millennia.

The vase – the acknowledged inspiration of eighteen and nineteenth century ceramicists such as Wedgewood and a host of lesser lights – is housed at the British Museum. Research by a team of Australian academics, however, has discovered that the precious work of art has been wrongly classified for centuries.

Specifically, by using a combination of computed tomography and mathematical analysis the researchers have shown that Roman cameo glass was not made by blowing, but by a different process known as “pate de verre”.

While glass-blowing involves basically inflating a balloon of molten glass by pushing air into it through a tube, pate de verre is a form of casting. Finely crushed glass particles are mixed into a paste with a binding material (and colours), which is then put on the inner surface of a mould and then fired.

Research on Roman cameo glass fragments led by Richard Whitely of the Australian National University (ANU) in Canberra focussed on studying the fine structure of air bubbles trapped between blue and white layers.

The collaboration between the university’s schools of art and design, classics, and physics and engineering revealed evidence that the glass could not possibly have been produced by blowing.

“We saw a bubble configuration within the glass that results from a pressing and turning motion,” says Whiteley.

“I believe that cold granulated glass has been packed into a mould and then a blob of molten blue glass introduced and pressed against mould heating the white granules from behind.

“You just would not get a bubble that size and flat-shaped from blowing.”

Whiteley’s findings were partly observational and experiential. As well as a teacher and researcher, he is a respected glass artist.

“I carve and shape glass with my hands, and have done for decades,” he says. “The marks I saw were inconsistent with what I see in my work.”

His conclusions were backed up by his colleague Tim Senden from the school of physics and engineering, who used the data from the tomographic scans and constructed mathematical models of the glass bubbles which were also incompatible with them having been created by blowing.

Whiteley will present his team’s findings at a meeting of The Association for the History of Glass to be held at the British Museum on November 4.