The
early modern period in England (c. 1500–1800) brought on a revival in local
glass
Glass is a non-crystalline, often transparent, amorphous solid that has widespread practical, technological, and decorative use in, for example, window panes, tableware, and optics. Glass is most often formed by rapid cooling (quenching) of ...
production.
Medieval glass had been limited to the small-scale production of
forest glass
Forest glass (''Waldglas'' in German) is late medieval glass produced in northwestern and central Europe from approximately 1000–1700 AD using wood ash and sand as the main raw materials and made in factories known as glasshouses in forest a ...
for window glass and vessels, predominantly in the
Weald
The Weald () is an area of South East England between the parallel chalk escarpments of the North and the South Downs. It crosses the counties of Hampshire, Surrey, Sussex and Kent. It has three separate parts: the sandstone "High Weald" in the ...
.
[Kenyon, G.H., 1967. ''The Glass Industry of the Weald'' Leicester, Leicester University Press] The organisation of production evolved from the small-scale family-run glass houses typical of forest glass-making to large monopolies granted by the Crown.
[Godfrey, E., 1975. ''The Development of English Glassmaking 1560-1640''. Oxford, Clarendon Press.] The influx of immigrants from Europe brought changes in
furnace
A furnace is a structure in which heat is produced with the help of combustion.
Furnace may also refer to:
Appliances Buildings
* Furnace (central heating): a furnace , or a heater or boiler , used to generate heat for buildings
* Boiler, used t ...
technology and raw materials, creating a better quality glass.
[Crossley, D.W., 1990. ''Post-Medieval Archaeology in Britain'' New York, Leicester University Press][Crossley, D.W., 1998. "The English Glassmaker and his search for materials in the 16th and 17th centuries." In McCray, P (ed) ''The Prehistory and History of Glassmaking Technology'', Westerville: Ohio, American Ceramic Society, 167-179] Monastic decrees later banned the use of wood fuel which was then replaced by the less expensive alternative of
coal
Coal is a combustible black or brownish-black sedimentary rock, formed as rock strata called coal seams. Coal is mostly carbon with variable amounts of other elements, chiefly hydrogen, sulfur, oxygen, and nitrogen.
Coal is formed when dea ...
.
[Willmott, H., 2005. ''A History of English Glassmaking AD 40-1800'', Tempus Publishing Limited] The development of
lead glass
Lead glass, commonly called crystal, is a variety of glass in which lead replaces the calcium content of a typical potash glass. Lead glass contains typically 18–40% (by weight) lead(II) oxide (PbO), while modern lead crystal, historically als ...
in the late 17th century propelled England to the forefront of the glass industry and paved the way for advancements in the
Industrial Revolution
The Industrial Revolution was the transition to new manufacturing processes in Great Britain, continental Europe, and the United States, that occurred during the period from around 1760 to about 1820–1840. This transition included going f ...
.
[Charleston, R. J., 1984. ''English Glass and the Glass used in England ca. 400-1940''. London, Allen and Unwin]
Chemical composition
Glass has three major components: a ''network former'' (silica), a ''network modifier'' (
flux
Flux describes any effect that appears to pass or travel (whether it actually moves or not) through a surface or substance. Flux is a concept in applied mathematics and vector calculus which has many applications to physics. For transport ph ...
), and a ''network stabilizer'' (predominantly lime).
[Terence Maloney, F.J., 1967. ''Glass in the Modern World''. Science and Technology Series. London, Aldus books.][Dungworth, D., 2003. ''Scientific Examination of Glass and Glassmaking Materials from Silkstone, Yorkshire''. Centre for Archaeology, English Heritage Report 90/2003] In the early 16th and 17th centuries glassmaking (the manufacture of glass from raw materials) and glassworking (the creation of objects from glass) occurred within the same glasshouse.
[Crossley, D.W., 1967. "Glassmaking in Bagot's Park, Staffordshire, in the Sixteenth Century." ''Post-Medieval Archaeology'' 1,67-72] Glass was also recycled at this time in the form of cullet.
In the early modern era, network formers were obtained from fine or coarse sands which were usually located near the area of production or from silica based pebbles.
Network modifiers were used to alter the chemical composition of the network former and reduce the melting temperature of the batch.
These fluxes varied depending on the type of glass.
Potassium oxide
Potassium oxide ( K O) is an ionic compound of potassium and oxygen. It is a base. This pale yellow solid is the simplest oxide of potassium. It is a highly reactive compound that is rarely encountered. Some industrial materials, such as fertiliz ...
(K
2O) based alkalis were used extensively in glass production.
The type of flux selected heavily influenced the quality of the glass produced. In England, beech wood and oak were preferred for forest glass.
For
soda-lime glass
Soda lime is a mixture of NaOH and CaO chemicals, used in granular form in closed breathing environments, such as general anaesthesia, submarines, rebreathers and recompression chambers, to remove carbon dioxide from breathing gases to prevent ...
(Na
2O), alkalis were often found in the form of marine plants – either local kelp or imported plants from the Mediterranean and the Near East (
barilla
''Barilla'' refers to several species of salt-tolerant (halophyte) plants that, until the 19th century, were the primary source of soda ash and hence of sodium carbonate. The word "barilla" was also used directly to refer to the soda ash obtained ...
, polverine, rochetta, sevonus,
natron
Natron is a naturally occurring mixture of sodium carbonate decahydrate ( Na2CO3·10H2O, a kind of soda ash) and around 17% sodium bicarbonate (also called baking soda, NaHCO3) along with small quantities of sodium chloride and sodium sulfate. N ...
).
These were often used for the production of 'white' ''crystallo'' glass, a colourless glass or ''
façon de venise
Venetian glass () is glassware made in Venice, typically on the island of Murano near the city. Traditionally it is made with a soda–lime "metal" and is typically elaborately decorated, with various "hot" glass-forming techniques, as well as ...
'', colourless glass of the highest quality.
[Willmott, H., 2002. ''Early Post-Medieval vessel Glass in England c. 1500-1670'' Council for British Archaeology, Research Report 132]
Network stabilizers in early modern England continued to be
lime
Lime commonly refers to:
* Lime (fruit), a green citrus fruit
* Lime (material), inorganic materials containing calcium, usually calcium oxide or calcium hydroxide
* Lime (color), a color between yellow and green
Lime may also refer to:
Botany ...
sources.
Lime occurs as a natural contaminant in most sands, and may also be intentionally added to the melt.
[Frank, S., 1982., ''Glass and Archaeology''. London: Academic Press]
Compositional groups
Five glass compositional groups have been identified through analysis of archaeologically recovered glass from this period.
[Henderson, J., 1998. "Post-Medieval Glass: Production, Characterization, and Value." In McCray, P (ed) ''The Prehistory and History of Glassmaking Technology'', Westerville: Ohio, American Ceramic Society, 33-61] These have been further reduced into two types, ‘green glass’ and ‘white glass’.
[Mortimer, C., 1995. "Analysis of Post Medieval Glass from Old Broad Street, London, with Reference to Other Contemporary Glasses from London and Italy." In Hook, D.R. and Gaimster, D.R.M. (eds) ''Trade and Discovery: The Scientific Study of Artefacts from Post-Medieval Europe and Beyond''. London: British Museum, 135-144][Dungworth, D., 2005. "The Scientific Study of Late 17th Century Glasswork at Silkstone, England." In AIHV and authors ''Annales du 16º Congrès de Association internationale pour l'histoire du Verre''. Bristol, J.W. Arrowsmith, 254-257]
The groups include:
*Potash-lime-silica glass (forest or green glass), typically has an excess of 10% wt oxide K
20
*High lime low alkali (green glass) usually has <10% Na
2O, K
2O, 15-20%
CaO Cao or CAO may refer to:
Mythology
*Cao (bull), a legendary bull in Meitei mythology
Companies or organizations
* Air China Cargo, ICAO airline designator CAO
*CA Oradea, Romanian football club
*CA Osasuna, Spanish football club
*Canadian Assoc ...
*Soda-lime glass (white glass/‘ordinary glass’) with low MgO, CaO, high K
2O
*Mixed alkali glass (white glass/''crystallo'') Na
2O K
2O and CaO levels are too low for this glass to be incorporated in the other categories.
*Lead glass (white glass/ ''façon de venise'') has on average 25-35%
PbO
The following table represents the mean compositional data derived from the analysis of materials at the Old Broad Street furnace in London, dated to the early 17th century.
and those recovered from Phase Two (circa 1680-1700 AD) Silkstone, Yorkshire
This information was gathered from Dungworth's compilation and analysis
The data is represented in wt% oxides and those below the detection limits (0.2% or less) are shown by '-'.
Colorants
There are numerous factors that may influence colouration during glass production. These include contaminants in raw materials, furnace conditions, and deliberate additives that would provide known colour variations.
Iron existing as a contaminant in sands, produced either a green or brown colour depending upon the oxidation state.
Coal fumes provided a carbon contaminant, which could create a dark brown or black colour.
Manganese present in wood ash may have contributed to the lighter, translucent green colour. Other trace elements present in alkalis (such as MnO in beech ash) undoubtedly influenced the finished product.
Other metal oxide colorants were known from earlier periods in
antiquity.
Early post-medieval glass
Medieval glasshouse traditions continued in the Weald, which was becoming deforested by the early 17th century; local glassmaking spread elsewhere, where timber was available to fire furnaces, to Hampshire, Gloucestershire, North Staffordshire and the Scottish Borders. At Bagot's Park, Staffordshire, one such glasshouse has been recovered, which dates from circa 1535; it contained an early melting furnace and a smaller annealing furnace.
The melting furnace had two siege benches for the placement of three
crucible
A crucible is a ceramic or metal container in which metals or other substances may be melted or subjected to very high temperatures. While crucibles were historically usually made from clay, they can be made from any material that withstands te ...
pots, each with a central flue cut into the floor to create a draught that would allow the furnace to achieve 1200 °C in order to melt the glass.
Fritting, and the preheating of crucibles may have occurred in the upper areas of the main furnace.
Annealing (glass)
Annealing is a process of slowly cooling hot glass objects after they have been formed, to relieve residual internal stresses introduced during manufacture. Especially for smaller, simpler objects, annealing may be incidental to the process of ...
and
glass blowing
Glassblowing is a glassforming technique that involves inflating molten glass into a bubble (or parison) with the aid of a blowpipe (or blow tube). A person who blows glass is called a ''glassblower'', ''glassmith'', or ''gaffer''. A '' lampworke ...
probably occurred using a smaller furnace. Cullet heaps of broken glass residue were found on either side, suggesting the use of a flux to reduce melting temperatures. Some crushed white pebbles were recovered in the bottom of pots, and this may reflect the silica source used at this site.
The glass recovered from Bagot's Park was badly weathered, yet the ends of
broad glass and
crown glass suggest that window and vessel glass were produced.
Glass technology
The majority of glass at this time was
blown or mould blown into a variety of vessel shapes.
This was enhanced by decorative styles, including optic decoration and trailing the glass, sometimes with pre-fabricated glass canes, to replicate Venetian traditions.
In glass tank furnace we generally used AZS block in bottom section.
Influences from the Continent
In 1567, Jean Carré arrived in London from Antwerp and obtained a crown-sanctioned patent for the production of window glass. This patent was awarded to Carré on the condition that prices remained low and that glassmaking and blowing would be taught to native Englishmen to promote the craft.
He brought many Venetian craftsmen to his London workshop and opened a second furnace outside the city to produce vessel and green glass.
Later in 1574, Jacob Verzelini, a Venetian who worked for Carré was granted a monopoly over Venetian-style vessel glass.
This effectively banned most of the imports from Venice and promoted glass made locally in England.
Verzelini's goal was to produce clear ''crystallo'' glass as well as decorative glass ''façon de venise'' ("in the Venetian mode"), which he achieved by importing
barilla
''Barilla'' refers to several species of salt-tolerant (halophyte) plants that, until the 19th century, were the primary source of soda ash and hence of sodium carbonate. The word "barilla" was also used directly to refer to the soda ash obtained ...
from Spain.
This effectively helped to lower the price of clear glassware and made it available to a wider range of the gentry and middle class.
Utilitarian green glass production remained on a small scale and was made by numerous glasshouses in different areas for local consumption, in the tradition of forest glass.
Technological changes
With the new influx of immigrants from the European Continent in the mid-16th century, technological changes affected the quality of English glass. This was possibly the combined result of experience and the selection/importation of purer raw materials.
Winged furnaces
Additionally, glass furnaces constructed from the mid-16th century began to reflect continental styles. This trend, identifiable in the archaeological record, supports the documentary evidence for immigrant glassmakers.
Wing-like additions were added to the late 16th–early 17th century furnace remains at two glass producing sites, Hutton and Rosedale in York, as well as at Vann Copse in the Weald.
[Aberg, F. A. and D.W. Crossley. 1972. "Sixteenth Century Glass-making in Yorkshire". ''Post-Medieval Archaeology'' 6, 107-159] The Hutton furnace had two wings added in the northeast and southeast corners of the original rectangular melting furnace.
A smaller nearby furnace was abandoned around the same time as the addition of the wings, suggesting that they provided an area for either annealing or pre-heating pots.
Rosedale and Vann Copse were constructed in similar styles but with four wings, one in each corner, which were built integral to the original furnace.
The wings showed evidence of heating which again suggested these were areas for fritting or glassworking. The glass produced at Rosedale was generally cleaner and of a better quality than that of Hutton, although the reasons for this are still unclear.
Production at Rosedale appeared to have a higher output than that of Hutton, as two additional smaller furnaces indicate that the operation had expanded.
It is thought that these furnaces are similar to those of the Lorraine style, and research in Belgium suggests that contemporary continental furnaces were made in this fashion.
[Terlinden, A.M. and Crossley, D.W. 1981. "Post-Medieval Glass Making in Brabant: the Excavation of a seventeenth-century furnace at Savenel, Nethen." ''Post Medieval Archaeology'', 15, 189-195]
Change to coal
From 1581–1584, Parliament became increasingly concerned over the wood supply in the country.
At this time, a large number of high temperature industries were dependent on wood for fuel, and this began to diminish the country's forests.
The original decree in this time prohibited the use of wood fuel unless it was from one’s own land.
By 1609,
Sir Edward Zouche was granted a patent to experiment with coal as the main fuel for a furnace at Winchester and by 1615 Parliament had banned the use of wood fuel.
Adopting coal as the main source of fuel created numerous problems for glass production. Burning coal produced short flames which shifted the location of the hearth from the far ends of the furnace to the center.
Air draughts are also necessary to create a regenerative heating system for glassmelting.
Early coal furnaces, such as at Bolsterstone, contain underground flues to provide an easy way to remove ash.
Additionally, the carbon from the coal fumes contaminated the glass in the uncovered pots which created a dark and often uneven colour. Lids, such as those found at Bolsterstone, needed to be implemented to prevent these impurities.
Glass bottles from this initial transition are often dark in color.
Sir Robert Mansell
Before 1616, Sir Robert Mansell bought out the patent and company started by Zouche.
He began many ventures and set up a successful glasshouse near a coal source in the attempts to save money and to more easily meet the demands of London.
His ''crystallo'' furnace at Broad Street, London, had fared successfully.
Some of his earlier attempts to set up new a furnace to produce glass for the growing needs of London failed, as transportation costs proved to be too high.
Yet the furnace Mansell set up at Newcastle was successful.
Another winged furnace was set up at
Kimmeridge
Kimmeridge () is a small village and civil parish on the Isle of Purbeck, a peninsula on the English Channel coast in Dorset, England. It is situated about south of Wareham and west of Swanage. In 2013 the estimated population of the civil p ...
using local sources of oil shale as fuel.
[Crossley, D.W., 1987. "Sir William Clavell's Glasshouse at Kimmeridge, Dorset Excavations from 1980-1981." ''Archaeological Journal'' 144, 340-382] Unlike other wing furnaces, the one at this site had deep flues and a centrally located hearth, illustrating the adaptation to a new fuel source.
This furnace was demolished in 1623 as being in violation of Mansell’s monopoly.
Conical furnaces
The conical glasshouses of England of the late 17th century introduced to furnaces the use of a chimney and a new plan shape.
This development possibly drew off the idea of earlier wind furnaces and the beehive-shaped Venetian style furnaces, known only from historical documents in England.
The addition of the chimney both created a strong draught and acted to extract the coal fumes.
The earliest examples appear in Bristol and at Gawber, Yorkshire.
These furnaces had underground flues and chimneys with air holes to provide a strong air draught to control heat.
Fritting, pre-heating pots and annealing processes were undertaken in different sections of the furnace, elevated above the heat source.
Expansion of the industry
Around 1663,
George Ravenscroft
George Ravenscroft (1632 – 7 June 1683) was an English businessman in the import/export and glass making trades. He is primarily known for his work in developing clear lead crystal glass (also known as flint glass) in England.
Personal life
L ...
developed
flint glass
Flint glass is optical glass that has relatively high refractive index and low Abbe number (high Dispersion (optics), dispersion). Flint glasses are arbitrarily defined as having an Abbe number of 50 to 55 or less. The currently known flint gl ...
, a colourless and translucent glass with many desirable working properties.
The original recipe was subject to
crizzling.
[Moretti, C. 2005 "English Lead Crystal: A Critical Analysis of the formulation attributed to George Ravenscroft." In ''Annales du 16º Congrès de l'Association internationale pour l'histoire de Verre London 2003''. Bristol, J.W. Arrowsmith] Later batches had the addition of lead oxide (
PbO) which combatted this problem and produced a superior glass that was more suitable for to engraving and etching. Lead glass was widely adopted by the Glass seller’s guild when Ravenscroft’s patent expired.
Lead glass helped to propel England to the front of the glass industry. Bottles for wine and phials began to be produced and exported on a large scale.
The archaeological remains of the ''Albion'' shipwreck off Margate in 1765 contained 11 lead glass
ingots, which are thought to be meant for trade with China.
[Redknap, M. and Freestone, I.C. "Eighteenth Century Glass Ingots from England: Further Light on the Post-Medieval Glass Trade." In Hook, D.R. and Gaimster, D.R.M. (eds) ''Trade and Discovery: The Scientific Study of Artefacts from Post-Medieval Europe and Beyond''. London: British Museum, 145-158] Although little is known about these materials, it does suggest that lead glass contributed to England's exports.
The 19th century brought new developments with synthetic materials, such as gas fuel.
Additionally, continuous melting production with tank furnaces helped mark the end of the early modern period and the beginning of the Industrial Revolution.
English glass objects
Vessel glass
The evolution of vessel glass became more elaborate and specific to its intended use throughout the early modern period.
Mirror glass and glass objects also began to be produced on larger scales during the early modern period. Types of objects include:
*Phials
*Goblets
*Drinking glasses
*Beakers
*Tankards
*Jugs
*Bottles
*Bowls
*Jars
*Urinals
*Flasks
*Mirror glass
Window glass
Window glass was produced throughout the period on a small scale, in the form of crown glass and broad glass.
This was predominantly made from green glass throughout the 16th century.
While rare in the early 16th century, glass windows soon became a symbol of increasing wealth and status. Larger sheets were in demand for domestic and public buildings.
Stained glass
Stained glass in the earliest part of the early modern period was imported into England from France.
With the
Protestant Reformation
The Reformation (alternatively named the Protestant Reformation or the European Reformation) was a major movement within Western Christianity in 16th-century Europe that posed a religious and political challenge to the Catholic Church and in ...
in England, ecclesiastic buildings increasingly used the more expensive 'white' glass.
References
{{DEFAULTSORT:Early Modern Glass In England
History of glass
Economic history of England
Glass
Glass is a non-crystalline, often transparent, amorphous solid that has widespread practical, technological, and decorative use in, for example, window panes, tableware, and optics. Glass is most often formed by rapid cooling (quenching) of ...
English design