Monday 13 May 2019

George Ravenscroft - 17th Century Pioneer in Glass

by Deborah Swift

I love the fact that writing historical fiction takes me up all sorts of byways. Whilst researching for my new book set in the mid 17th Century, I wondered what sort of glasses they might have drunk from, and whether by then, it would still be pewter or horn. When did glass make an appearance for the everyday person? Not early enough for my book apparently, for though glass for windows and chunky simple cups had been made in England since the 13th Century, the impurities in the glass made it brittle and unsuitable for fine tableware. Fine glass was imported, usually from Venice. But in the later 17th Century a new method was developed by George Ravenscroft - a method that would mean England could produce its own glass to rival that of the Italians.

Anglo-Venetian glass with Dutch engraving - National Gallery of Victoria
George Ravenscroft was a trader in goods such as currants, glass, and lace. During the years he was trading, and before he arrived in London in 1666, he lived in Venice. Being involved in the glass trade, he was able to observe the method used by glassmakers in Italy, but soon came up with his own version of glass manufacture, using a mixture which was produced with a high lead content. Experiments he made between 1674 and 1676 gave a brilliant transparent and hard-wearing heavy glass which we now know as 'lead crystal.'

Secret Formula

The circumstances surrounding Ravenscroft’s role in the invention of lead crystal are not very clear. 17th Century records of the manufacturing process are incomplete, but moreover, Ravenscroft was rather secretive about his ingredients and processes. He was wary, as one might expect, of competitors copying him.

It is thought he had assistance from Sir Robert Plot FRS, who had the idea of using flints from Oxfordshire river beds. In Murano, Italy, where the best glass of the era came from, very expensive white flints from the River Po were used. Historians cannot agree on how Ravenscroft was inspired to use lead in the production of glass. Was it an accident, or had he pinched the idea of adding lead oxides to the glass from the glassmakers of Venice? To add to the confusion, an Italian book about glass making - L'Arte Vetraria, written by Antonio Neri in 1612, was translated into English by Christopher Merrett in 1662. Here's a quotation from the book describing lead glass when molten:

"This sort of glass, lead glass, is so runny that were it not cooled, and taken up by turning to wind a gather, it would be impossible to work. It is so runny that it would not even hold onto the punty, because it is as loose as soup. This arises out of the lead calx causes it to become very fluid."


Adding lead oxide to the glass made it less viscous than ordinary glass when heated. Because of this, it could be worked for longer without re-heating. The early glass Ravenscroft made was subject to developing a crackled surface known as crizzling, (what a lovely word!) caused by too much potash in the mix. But by1676 Ravenscroft had improved the glass, making lead glass, which contained a higher quantity of lead oxide, thus preventing crizzling. Lead glass has a higher refraction that previous English glass, making it sparkle, and ring like a bell if you gently strike the edge.

A well-crizzled decanter from the V&A 

Unique Glass Patent
Ravenscroft was granted a patent from King Charles II in 1674 to be the sole manufacturer of lead crystal in England. His prices were one shilling for a claret glass, rising to one shilling and eight pence for the heavier beer glass. Ale at this time was a strong drink that required a bowl of four fluid ounces, whereas a wine glass held only two. Because of Ravenscroft's invention, the prices of glasses dropped steeply until by the end of the century it was six shillings a dozen.

A George Ravenscroft glass, also in the V&A

Ravenscroft's was a short but glittering career that lasted only five years,as he closed his manufacturing business in Henley-on-Thames in 1679. The following year he joined the Vauxhall glassworks, working with the company until his death in 1683. By the late seventeenth century, the trade in Venetian glass was in serious decline, whilst in England there was a boom in glass manufacture. The English couldn't get enough of this light, clear glass and it was produced in ever-growing quantities to meet burgeoning demand at home and abroad.

Read more about it from Glass Historian David C Watts

English Drinking Glasses - L M Bickerton
History of Glass - Dan Klein and Ward Lloyd

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1 comment:

Susan Price said...

I rather like the crizzled glass!