We take clear glass or Cristallo for granted today but this fragile material was once so prized men were condemned to death for revealing its secrets.
Sparklingly clear glass is the stuff of romance. Without it there would be no coup de champagne or glittering chandeliers to dance under and no cheap sparkles for a girl to wear.
The Venetians had been making glass since Roman times but by the late 1200s, the production of glass objects of the finest quality was the city’s major industry. The Glassmakers Guild laid out rules and regulations to safeguard their secrets and in 1271 a law prohibited the importation of foreign glass or the employment of foreign glass workers. An even more radical law was passed in 1291 that laid the ground for the establishment of Murano as a premier glass-manufacturing centre. This law required that all furnaces used for glass making be moved from Venice to the island of Murano to avoid the risk of in the overpopulated city. Many historians agree that the real motive was to isolate the glassmakers to a place on where they wouldn’t be able to disclose trade secrets. A subsequent law passed in 1295 forbidding the glassmakers from leaving the city on pain of death confirms this theory.
Venetian glass reached the peak of its popularity in the 15th and 16th centuries. In the 15th century, master Angelo Barovier discovered the process for producing clear glass – (Cristallo) – that allowed Murano glass makers to become the only producers of mirrors in Europe. In addition, the popularity of Chinese porcelain among European nobility fuelled the discovery and production of the white glass mimicking porcelain (lattimo). Other types of glass making techniques became popular such as enameling and gilding glass, which originated in the Middle East, filigrana glass which is made using glass rods with inner threads of white, golden or coloured glass that are twisted or intersecting, and ice glass which appears finely crackled. Variety of shapes and colours increased, and glassware became more sophisticated though the beauty was still viewed as the simplicity of shapes and ornaments.
By the end of the 16th-century glasshouses in Bohemia, Germany, the Low Countries, and even England were employing Italian glassmakers to produce a colourless glass, an imitation of Venetian Cristallo, often called façon de Venise. However, a century later things were beginning to change. Coal was a major factor. Coal fired furnaces were developed in England and towards the end of the 17th century, the first colourless lead glass (variously called ‘flint glass’ and ‘lead crystal’) was produced. These new technologies allowed Britain to become one of the leading glass producers and the balance of power in the world of glass began to shift northwards.
This shift from Venetian Cristallo glass to northern European imitations (façon de Venise) was noted by Girolamo Alberti, the Doge of Venice’s Secretary in London in October 1672 when he complained that “With regard to Venetian trade, I find that of glass is utterly ruined since the introduction here of the manufacture of mirrors and drinking glasses, by a privilege granted to the Duke of Buckingham.”
The origin of colourless lead glass is traditionally traced back to George Ravenscroft and his 1674 patent. However, the details of what Ravenscroft actually invented are obscure. Recent research points to an Italian connection. Ravenscroft, set up a furnace in Savoy. The Savoy glasshouse was visited 29 July 1673 by Robert Hooke and Christopher Wren. Hooke records that they visited, the new glasshouse at the Savoy and “saw calcind flints as white as flower, Borax, Niter and tarter, with which he made his glasse he denyd to use arsenick he shewd pretty representations of Agates by glass &c.”
It is more likely that Ravenscroft was a financial backer and that an Italian glassmaker called Da Costa was the actual inventor of the glass that was patented. John Baptista Da Costa was one of two glassmakers from Altare, the other was John Odaccio Formica, who worked together in Nijmegen between 1665 and c.1672. Both were later associated with lead glass industries: Da Costa in London and Odaccio in Dublin.
On the 8th March of 1674, George Ravenscroft petitioned the crown for a patent to produce glass as it was still legally in the hands of the Duke of Buckingham. Ravenscroft claimed to have ‘attained to the art and manufacture of a particular sort of Cristaline Glasses resembling Rock Cristall, not formerly exercised or put into use’. The patent was for drinking glasses and specifically excludes mirrors as well as, other sorts of glasse of ancient fabrick, at present and for many years practiced or any other sort of glasse that shall be made by others. The King approved the application on the 19th March and the patent was formally issued on the 16th May 1674 for a period of seven years. That year Ravenscroft entered into an exclusive agreement with the Company of London Glass Sellers to provide them with his new glassware.
The new process had its teething problems, namely crizzling, where the glass became flaky and lost transparency. The problem it seems was solved by adding more lead to the mixture. By the 1680s glass, manufacture had spread outside London to Bristol and Newcastle-upon-Tyne. Archaeological evidence from the glasshouse at Silkstone, South Yorkshire shows the production of lead glass during the 1680s using coal.
The Glass Sellers sought to ban imports of so-called ‘country’ glasses into London during the 1680s. They argued that the ‘country’ glasses were of inferior quality and that the London consumer needed to be protected. It is perhaps more likely that those most in need of protection were the members of the Company of Glass Sellers!
Sources:
Investigation of Late 17th Century Crystal Glass, D Dungworth and C Brain, Centre for Archaeology Report 21/2005
https://www.glassofvenice.com/murano_glass_history.php
Julia Herdman writes historical fiction that puts women to the fore. Her latest book Sinclair, Tales of Tooley Street Vol. 1. is Available on Amazon – Paperback £10.99 Kindle £2.42 Also available on:
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