kb/data/en.wikipedia.org/wiki/History_of_glass-3.md

title	chunk	source	category	tags	date_saved	instance
History of glass	4/5	https://en.wikipedia.org/wiki/History_of_glass	reference	science, encyclopedia	2026-05-05T03:59:48.666461+00:00	kb-cron

Anglo-Saxon glass has been found across England during archaeological excavations of both settlement and cemetery sites. Glass in the Anglo-Saxon period was used in the manufacture of a range of objects including vessels, beads, windows and was even used in jewelry. In the 5th century AD with the Roman departure from Britain, there were also considerable changes in the usage of glass. Excavation of Romano-British sites has revealed plentiful amounts of glass but, in contrast, the amount recovered from the 5th century and later Anglo-Saxon sites is minuscule. The majority of complete vessels and assemblages of beads come from the excavations of early Anglo-Saxon cemeteries, but a change in burial rites in the late 7th century affected the recovery of glass, as Christian Anglo-Saxons were buried with fewer grave goods, and glass is rarely found. From the late 7th century onwards, window glass is found more frequently. This is directly related to the introduction of Christianity and the construction of churches and monasteries. There are a few Anglo-Saxon ecclesiastical literary sources that mention the production and use of glass, although these relate to window glass used in ecclesiastical buildings. Glass was also used by the Anglo-Saxons in their jewelry, both as enamel or as cut glass insets.

==== Murano ====

The center for luxury Italian glassmaking from the 14th century was the island of Murano, which developed many new techniques and became the center of a lucrative export trade in dinnerware, mirrors, and other items. What made Venetian Murano glass significantly different was that the local quartz pebbles were almost pure silica, and were ground into a fine clear sand that was combined with soda ash obtained from the Levant, for which the Venetians held the sole monopoly. The clearest and finest glass is tinted in two ways: firstly, a natural coloring agent is ground and melted with the glass. Many of these coloring agents still exist today; for a list of coloring agents, see below. Black glass was called obsidianus after obsidian stone. A second method is apparently to produce a black glass which, when held to the light, will show the true color that this glass will give to another glass when used as a dye. The Venetian ability to produce this superior form of glass resulted in a trade advantage over other glass producing lands. Murano’s reputation as a center for glassmaking was born when the Venetian Republic, fearing fire might burn down the city’s mostly wood buildings, ordered glassmakers to move their foundries to Murano in 1291. Murano's glassmakers were soon the island’s most prominent citizens. Glassmakers were not allowed to leave the Republic. Many took a risk and set up glass furnaces in surrounding cities and as far afield as England and the Netherlands.

==== Bohemia ====

Bohemian glass, or Bohemia crystal, is a decorative glass produced in regions of Bohemia and Silesia, now in the current state of the Czech Republic, since the 13th century. Oldest archaeology excavations of glass-making sites date to around 1250 and are located in the Lusatian Mountains of Northern Bohemia. Most notable sites of glass-making throughout the ages are Skalice (German: Langenau), Kamenický Šenov (German: Steinschönau) and Nový Bor (German: Haida). Both Nový Bor and Kamenický Šenov have their own Glass Museums with many items dating since around 1600. It was especially outstanding in its manufacture of glass in high Baroque style from 1685 to 1750. In the 17th century, Caspar Lehmann, gem cutter to Emperor Rudolf II in Prague, adapted to glass the technique of gem engraving with copper and bronze wheels.

== Modern glass production ==

=== New processes ===

A very important advance in glass manufacture was the technique of adding lead oxide to the molten glass; this improved the appearance of the glass and made it easier to melt using sea-coal as a furnace fuel. This technique also increased the "working period" of the glass, making it easier to manipulate. The process was first discovered by George Ravenscroft in 1674, who was the first to produce clear lead crystal glassware on an industrial scale. Ravenscroft had the cultural and financial resources necessary to revolutionise the glass trade, allowing England to overtake Venice as the centre of the glass industry in the eighteenth and nineteenth centuries. Seeking to find an alternative to Venetian cristallo, he used flint as a silica source, but his glasses tended to crizzle, developing a network of small cracks destroying its transparency. This was eventually overcome by replacing some of the potash flux with lead oxide to the melt. He was granted a protective patent in where production and refinement moved from his glasshouse on the Savoy to the seclusion of Henley-on-Thames. By 1696, after the patent expired, twenty-seven glasshouses in England were producing flint glass and were exporting all over Europe with such success that, in 1746, the British Government imposed a lucrative tax on it. Rather than drastically reduce the lead content of their glass, manufacturers responded by creating highly decorated, smaller, more delicate forms, often with hollow stems, known to collectors today as Excise glasses. The British glass making industry was able to take off with the repeal of the tax in 1845. Evidence of the use of the blown plate glass method dates back to 1620 in London and was used for mirrors and coach plates. Louis Lucas de Nehou and A. Thevart perfected the process of casting polished plate glass in 1688 in France. Prior to this invention, mirror plates, made from blown "sheet" glass, had been limited in size. De Nehou's process of rolling molten glass poured on an iron table rendered the manufacture of very large plates possible. This method of production was adopted by the English in 1773 at Ravenhead. The polishing process was industrialized around 1800 with the adoption of a steam engine to carry out the grinding and polishing of the cast glass.

=== Industrial production ===