Billy Warren, Research Volunteer at the Museum, delves into the history of glass and its use in windows as part of our project to conserve three windows in our collection. A 17th Century Window, a stained glass Titanic memorial window and a sign from Olivers Butchers. You can read about this project here.

Evidence of using glass in windows dates back to the 1st century when Romans were casting glass
into flat panes. This glass was much thicker than the glass we know today and was translucent and
slightly tinted. The casting process was difficult and expensive, meaning glass was only used in the
windows of public buildings or the villas of the wealthy. The refinement of glass-blowing
techniques produced thinner, more transparent results; this meant that it became the primary method
of sheet glass production.

Nonetheless, before the 1500s, only houses of the exceedingly rich had glass in their windows and
most domestic windows in Britain were fitted with other coverings, such as wooden shutters.
Techniques brought over by glassmakers from Lorraine meant that glass able to be used for
windows was being manufactured in England from around the 1560s. Thanks to this and perhaps
also prompted by the chillier climate of the ‘Little Ice Age’, window glass became a more common
feature of expensive houses in the later half of the 16th century. Glass was much more effective than
wooden shutters or fabric coverings at stopping draughts, making it even more useful in keeping out
the cold.

Glass was also becoming more readily available. English glass manufacture began to increase at the
start of the 17th century when coal started to be used as a fuel rather than wood. What had
previously been a more limited ‘forest industry’ had grown into something with great potential. As
glass became more affordable in the 17th century, it was included in more ordinary domestic
buildings. During this period, the design was also changing from using glass ‘quarries’ (small,
usually diamond-shaped pieces attached together with lead) to having larger panes.

When James I banned glassmakers from using wood as fuel in 1615, he effectively handed a
monopoly on glass manufacture to one of his courtiers Robert Mansell. Mansell, who would later
go on to be one-time MP for Lostwithiel, was part of the company with the patent for coal-fired
glass furnaces. He quickly bought his partners out, giving him near-complete control of the industry
in England. Mansell poured almost all of his estate into his glass business. He spent £28,000 to
employ glassworkers from Venice, France and the Low Countries and set up glass furnaces outside
London – the most successful location ended up being Newcastle-upon-Tyne. Mansell’s monopoly
soon came under attack, being held to scrutiny in Parliament in 1621 and 1624. However, he kept
hold of it until 1642 and continued to own the glassworks in Newcastle until he died a decade
later.

For most of the medieval and early modern periods, English glass was regarded as poorer quality
than glass made in Europe. It was cheaper than imported glass and used for clear windows; any
coloured glass for medieval windows was European, not English. One reason for this was that the
materials available for making glass in England were generally seen as inferior to those available to glassmakers in Europe, especially those in Venice, who controlled the trade of many ingredients
necessary for the finest types of glass. 17th-century scientist Christopher Merret spent a great deal
of time seeking materials from the British Isles that would rival the quality of continental
ingredients. Among his suggestions for non-imported substitutes, Merret proposed zinc ore deposits
“sometimes … found in the mountanous [sic] parts of Cornwall” as an alternative to the zinc oxide
colourings from Holland and Poland. It is unclear to what extent this advice was heeded, but
English glass quality nonetheless increased with new types of glass and furnace designs.

Unsurprisingly, as glass became affordable for a wide range of people, demand for it increased.
Plate glass began to be manufactured in England in the 18th century and the first company
manufacturing it was founded in 1773. Plate glass allowed for even larger panes to be produced,
resulting in window glass becoming cheaper. By the end of the 18th century, glazed windows would
have been found in most houses, even those of the working class. Window glass merchants started
to appear and the number of glass warehouses increased: in London, the number rose from five in
1763 to thirteen by 1790. In a brief Cornish trade directory in 1783, there is no mention of glaziers
or glass merchants. Any glass would have had to be ordered specially from further afield.
However, by 1830, glaziers are listed in Liskeard, Penryn, Penzance, Redruth, St Austell, Stratton
and Truro.

The ready availability of glass would have fundamentally changed everyday life, with transparent
windows prompting entirely new behaviour. Now windows were valued not just for allowing light
into buildings, but for allowing people inside to see outside. Dictionary-writer Samuel Johnson
suggested that the sash window was created for ‘the sake of seeing and being seen’ – with glass
windows, people-watching went both ways! Shops recognised that people being able to see inside
also allowed them to see what they could buy. Starting with drapers shops in London using
windows to show the fabrics available, large windows quickly became not just fashionable but
standard for retail businesses. With eye-catching window displays, shops encouraged passers-by to
look at what was on offer.

Billy Warren, research volunteer.

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