Illuminating Objects - Filigree Drinking Glasses

FILIGREE DRINKING GLASSES
24/7-13/10/2013

FROM VENICE TO LONDON: THE MOVEMENT OF GLASS TECHNOLOGY
Canaletto, The Doge's Palace and the Piera del Bando, Venice, etching, c.1741-44. The Samuel Courtauld Trust, The Courtauld Gallery, London

Venice was famous for its luxury glassware. Some of the shapes are fanciful and fantastic. The fast drying Venetian soda glass meant intricate designs could be crafted.
Jacob Verzelini was one of the most influential Italian glassblowers to immigrate to England.

By the 13th century Venice was famous for its glass. The Venetian lagoon was in prime position for international trade and had a monopoly on luxury glassware. The Venetian Republic guarded their technology by restricting the movements and freedoms of their craftsmen, confining them and their industry to the island of Murano.

Despite strict regulations, many Venetians did leave Murano. By the 16th century, lured by the promise of greater freedoms and emerging markets in new locations, Italians had settled in new glassmaking centres across Europe. Initially craftsmen moved to Antwerp, which was one of the most important ports on the European Continent. Many glassblowers settled there and established glasshouses, unable to return to their homeland for fear of punishment. Some continued further North towards England, including the influential glassmaker Jean Carre in 1567 as well as Jacob Verzeliniho took over Carre’s glasshouse when he died in 1572. The Muranese had brought their skills and knowledge with them to these new destinations where they trained local people in their craft and made glass in the Venetian style, known as façon de venise. The glass made in these European locations was just as delicate and luxurious as the glass produced in Venice.

FILIGREE DRINKING GLASSES
A NEW MATERIAL: LEAD GLASS
For centuries the influence of Venice had stretched far and wide. But by the late 1600s Venetian influence in glass technology began to fade as a revolutionary recipe created in England in 1674 became popular. George Ravenscroft is credited with the creation of lead glass (then known as flint glass due to the use of powdered flint as silica) in which lead oxide was added to the molten glass batch. Lead glass was not only stronger and more durable but also clearer than Venetian glass. The large proportions of lead in the glass, up to 40% in some glasses, means it is very stable. The network of molecules in the glass is tightly held together so when the glass is struck the network cannot absorb the shock and instead vibrates in place. This gives lead glass a characteristic ring when tapped. This characteristic ring is absent in Venetian glasses. Lead glass is less viscous and takes much longer to cool and solidify than the façon de Venise glass. This dictated the sort of styles possible in lead glass. The fanciful designs of Venice gave way to more practical and straightforward shapes. Individual glasses were now constructed from three components, the foot, the stem and the bowl, made separately and then joined together in a production line typical of the industrialisation taking place at the time. Ornament was added to the glasses by engraving patterns onto them or in the form of decorative stems. Air twist stems were briefly popular around 1750 but were replaced by opaque twist stems (also known as cotton twist). English glass blowers used the filigree technique invented in the 16th century to produce increasingly complex patterns in the stems of glasses. One column of threads was sometimes surrounded by another, creating beautifully intricate interweaving designs.

FILIGREE DRINKING GLASSES
CRAFT AND COMPOSITION
X-ray fluorescence testing (using the Brucker X-ray fluorescence spectrometer) on this 16th century goblet revealed significant impurities, suggesting the glass is not cristallo but is more likely to be Vitrum Blanchum, a less refined type of glass.
Venetian glass is made of two major components: silica and flux. The Venetians used crushed pebbles from the Ticino River as their source of silica. The flux, which helps the silica to melt at a lower temperature, came from the ash of burned coastal plants. The ash also contained impurities which acted as stabilisers in the glass, without which the glass would be fragile and vulnerable to moisture in the air. Typically the stabiliser is lime, known to chemists as calcium oxide. There is little evidence that the Venetians realised the importance of adding stabilisers to their glass, so the presence of naturally occurring stabilisers in the flux was important. However, as well as stabilising impurities the ash contained other compounds which gave the glass a coloured hue instead of the crystal clarity the Venetians desired.

A recipe for cristallo glass, invented in the 1450s by Angelo Barovier, promised better transparency through purifying the ash of compounds which would colour it. The purification process inadvertently also removed the naturally occurring stabilisers meaning the glass was also very fragile and prone to glass diseases. Much academic debate revolves around whether or not cristallo glass has survived. Some experts claim that it is unlikely that large quantities of such fragile glass would have survived unscathed through the centuries. Despite this, many museum labels do refer to their glasses as cristallo simply to describe the very clear and feather-light nature of the glass rather than in reference to the use of Angelo Barovier’s purification technique.

Though much scientific research is currently underway on glass it is still difficult to distinguish Muranese glass from glass made in Northern European glass-making centres. Venetians who moved to Northern Europe brought their recipes with them and continued to use the same raw materials, meaning glasses made in Europe and in Venice have very similar chemical compositions. These recipes remained popular across Europe until the invention of lead glass in the late 17th century.

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