iridiscent stone

A Thirst for Innovation: Looking at the Technique

Venetians have excelled in the production of exquisite glassware for many centuries. The glassmaking industry, situated on the Venetian island of Murano, is thought to have reached its peak in the quality and innovation of its production between 1520 and 1540 when its craftsmen found the formula to make glass perfectly colourless. This glass was known as cristallo and became the hallmark of Venetian prestige and technical skill in glassmaking. Having perfected colourless transparency, Venetian glass-makers kept pushing their technical boundaries in other directions. They were thirsty for re-invention.

A close-up image of aventurine inclusions within chalcedony glass. Chalcedony and Aventurine Glass Bowl. Murano (Venice), 18th century, The Courtauld Gallery, London

In the late 17th and 18th centuries, glassmakers developed new materials and accomplished new visual effects. They sought to make coloured glass, which imitated precious stones and minerals, such as chalcedony or, as in this case, opals. Craftsmen were also highly skilled in obtaining complex forms through manipulating the molten glass with specialised tools such as pincers, by blowing it into moulds, and by combining various techniques. 

This exquisite glass bowl bears testimony to the high standards of Venetian glassmakers during this period. It imitates opal, a mineraloid or non-crystalline mineral with different material densities ranging from semi-transparent to opaque, and which can be either iridescent or opalescent similar to a milky appearance. The stone, which today is called opal, was known by the Italian word for sunflower, girasol, in the early 17th century, a reference to its changing aspect under various lighting conditions. 

Opalescent glass bowl under different light conditions. The Courtauld Gallery, London

When light passes through the milky white-bluish tones of this opalescent glass, its hues vary from oranges to fiery reddish colours, creating a visual effect which enhances the superb skills of the craftsmen. 

The light ribbing on the bowl is a strong indicator that this piece was first blown into a mould, with the handles being added later. The crests on the handles were made by pinching the molten glass with the help of pincers. 

Opalescent glass bowl under different light conditions. The Courtauld Gallery, London