Early Modern Glass England Revival
From around 1500 to 1800, England saw a major revival in its glassmaking industry. Before this time medieval glass had been mostly small scale and limited to forest glass used for basic windows and simple vessels. Most of this was made in the Weald region. Over time production grew larger, and glassmaking moved from small family operations into Crown-controlled monopolies.
European Influence on Glassmaking and Furnace Technology
Skilled workers who came from Europe introduced new furnace designs and raw material choices. These changes improved the clarity and strength of English glass. As the industry modernised, England switched from burning wood to coal fuel. Monastic rules banned wood fuel and coal proved to be more affordable and effective.
The Rise of Lead Glass
By the late 1600s England began producing lead glass. This material was clearer and easier to shape than earlier forms. Its introduction helped position England as a leading glass producer. The innovations in lead glass also laid groundwork for later industrial progress during the Industrial Revolution.
Understanding Glass Components
Glass is made of three essential parts. The first is the network former, usually silica. The second is the network modifier, known as a flux, which lowers the melting temperature. The third component is a stabilizer, in early England mainly lime.
Glassmaking and Glassworking Together
In the 16th and 17th centuries the same workshops would handle both glassmaking, turning raw materials into molten glass, and glassworking, shaping that glass into final products. Recycling was also common, turning broken glass or cullet back into usable material.
Sources of Silica for Network Formers
The silica needed for glass came from various sands or silica pebbles. These raw materials were often sourced locally, helping keep production costs down.
Role of Flux in Glass Quality
Flux was essential because it changed how easily the silica melted. Different types of flux affected the final glass quality. In England, potash-based alkalis like potassium oxide were common. For soda-lime glass, sodium oxide came from marine plants. This included local kelp and imported sea plants such as barilla from the Mediterranean, sevonus from the Near East, and natron. These alkaline fluxes were essential in making high-quality colourless glass known as crystallo or façon de venise.
Network Stabilizers and Lime Use
Lime acted as the stabilizer, and it was either naturally mixed with silica sand or added deliberately. Lime helped strengthen the glass and make it more durable.
Glass Composition in Early Modern England: Green and White Varieties
Introduction to Glass Types
Archaeological research has identified five compositional groups of glass from early modern England. These groups have been categorized into two main types: green glass and white glass. Green glass typically includes potash‑lime‑silica and high‑lime low‑alkali varieties. White glass covers soda‑lime compositions, mixed alkali glass, and lead glass.
Potash‑Lime‑Silica Glass (Forest or Green Glass)
Potash‑lime‑silica glass, often known as forest glass or green glass, is marked by more than 10 percent potassium oxide by weight. Analysis of materials from the Old Broad Street furnace in London shows that potash glass had around 2.5 percent sodium oxide, 6.5 percent magnesium oxide, 1.4 percent aluminum oxide, and 54.7 percent silica. It also contained roughly 11.8 percent potassium oxide and 14.5 percent calcium oxide. Trace elements included phosphorus pentoxide, sulfur trioxide, chlorine, titanium oxide, manganese oxide, iron oxide, and strontium oxide.
High‑Lime Low‑Alkali Glass (Green Glass)
The high‑lime low‑alkali type, another green glass, contains less than 10 percent combined sodium and potassium oxide, with calcium oxide between 15 and 20 percent. At Old Broad Street this glass had about 3 percent sodium oxide, 4 percent magnesium oxide, 3.3 percent aluminum oxide, and 57.9 percent silica. It also included around 4.6 percent potassium oxide and 20.7 percent calcium oxide. Similar data from Silkstone Phase Two (circa 1680 to 1700) in Yorkshire show compositions like 1.1 percent sodium oxide, 5.1 percent magnesium oxide, 4.5 percent aluminum oxide, 52.5 percent silica, 8.5 percent potassium oxide, and 21.4 percent calcium oxide.
Soda‑Lime Glass (White or Ordinary Glass)
Soda‑lime compositions, classified as white or ordinary glass, have low magnesium and calcium oxides along with elevated potassium oxide. The Old Broad Street analysis showed soda‑lime glass contained about 12.2 percent sodium oxide, 3.9 percent magnesium oxide, 1 percent aluminum oxide, and 68.6 percent silica. It had smaller amounts of phosphorus pentoxide, sulfur trioxide, chlorine, and potassium oxide, with calcium oxide at around 10.1 percent.
Mixed Alkali Glass (White or Crystallo Glass)
Mixed alkali glass, another white variety, features sodium, potassium, and calcium oxide levels too low to fit other categories. At Old Broad Street this type had about 6 percent sodium oxide, 5.3 percent magnesium oxide, 2.6 percent aluminum oxide, 63.5 percent silica, 3.6 percent potassium oxide, and 15.2 percent calcium oxide. From Silkstone Phase Two data shows it contained around 6.9 percent sodium oxide, 2.9 percent magnesium oxide, 1.4 percent aluminum oxide, 68.3 percent silica, 6.6 percent potassium oxide, and 10.5 percent calcium oxide.
Lead Glass (White Glass or Façon de Venise)
Lead glass, also known as couleur de venise, contains about 25 to 35 percent lead oxide. Silkstone Phase Two analysis recorded lead glass composition with less than 0.05 percent sodium oxide, under 0.3 percent magnesium oxide, 0.5 percent aluminum oxide, and 53.8 percent silica. It included about 13.2 percent potassium oxide and 32 percent lead oxide. Other oxides such as calcium, magnesium, sodium, phosphorus, sulfur, chlorine, titanium, manganese, and iron were present at levels below detection or under 0.2 percent.
Compositional Data Comparison
These compositional analyses come from investigations at Old Broad Street in London, dated to the beginning of the seventeenth century, and from Silkstone Phase Two in Yorkshire, around 1680 to 1700. The data was compiled and interpreted by Dungworth. The oxide weight percentages reveal how silica, alkalis, lime, and lead varied across types.
Factors Affecting Glass Colour
The final hue of glass during production depended on factors such as impurities in raw materials, furnace conditions, and the intentional use of additives for colour. Even a small change in composition or temperature could change the resulting shade of glass.
Iron Contamination in Early Modern English Glass
Sand used for glass often contained iron that caused green or brown hues depending on whether it was oxidized or reduced. Coal smoke added carbon, turning glass dark brown or nearly black. Ash from wood, which contained manganese, sometimes lightened the glass to a translucent green. All these trace elements in fluxes like beech ash influenced the final color.
Metal Oxide Colorants from Antiquity
Use of metal oxide colorants was not new; ancient glassmakers already knew how to color glass with various oxides.
Forest Depletion and New Glassmaking Sites
Glassmaking followed timber. Medieval glass traditions continued in the Weald, but deforestation by the early 1600s forced glasshouses to new locations. Hampshire, Gloucestershire, North Staffordshire, and the Scottish Borders became new centers for glass production.
Archaeological Evidence at Bagot’s Park
A glasshouse excavated at Bagot’s Park, Staffordshire, dates to around 1535. This site included a large melting furnace and a smaller annealing furnace. The melting furnace had two benches for three crucibles, each with its own flue to channel airflow. This design let it reach up to 1200 °C. Above the crucibles, molten glass may have been preheated. The smaller furnace nearby was likely used for annealing and glass blowing. Broken glass shards or cullet were piled beside the furnaces, hinting at reuse and fluxing in production. Fragments of white silica pebbles in crucibles suggest the raw silica source. Although the glass showed heavy weathering, remnants of broad window panes and crown glass vessels confirm that this site made both flat and container glass.
Blown Glass Techniques and Decorative Styles
Most glass products were blown or mold-blown into vessels. Craftsmen added decoration like optic ridges and trails using glass canes, imitating Venetian techniques popular at this time.
Venetian Influence Arrives in London
In 1567, Jean Carré moved from Antwerp to London and received a royal license to produce window glass. The patent required affordable prices and training of English workers in glassmaking and blowing. Carré employed Venetian artisans and later opened a second furnace outside London to manufacture green and container glass.
Monopoly on Venetian-Style Glass
Seven years later, in 1574, Carlé’s associate Jacob Verzelini, a Venetian, was granted exclusive rights to produce Venetian-style vessel glass. Imports from Venice were effectively blocked, fostering domestic production. Verzelini focused on making clear crystallo glass and decorative façon de venise pieces. To do this he imported barilla from Spain to use as soda flux. This lowered costs and made clear glassware more accessible to gentry and merchants.
Continued Overview of Early Modern English Glass Production
Utilitarian Green Glass and Local Glasshouses
In early modern England, green glass stayed modest in production. Glasshouses across various regions crafted it for nearby consumption. This tradition followed the earlier forest glass model, focused on functional glass rather than fine, clear varieties.
Impact of Mid‑16th Century Immigrants on Glass Quality
When skilled glassmakers arrived from Europe in the mid‑1500s, they brought advanced skills and purer raw materials. These changes helped enhance English glass quality. Archaeological findings and historical records both confirm their influence on furnace design and production methods.
Changes in Furnace Architecture
Starting in the mid‑1500s, English glass furnaces began to mirror continental styles. Excavations at Hutton and Rosedale in York, and at Vann Copse in the Weald, all show new additions shaped like wings. At Hutton a rectangular furnace received two wings in the northeast and southeast corners. A nearby smaller furnace was abandoned at the same time, suggesting the wings added space for either annealing cooled glass or pre‑heating pots.
Rosedale and Vann Copse expanded this idea further. Their furnaces had four wings, one at each corner. All these winged areas bore signs of heat exposure, indicating they served either fritting or glassworking tasks. Glass from Rosedale tends to be clearer and of higher quality than that from Hutton, though the precise reasons remain unclear. Rosedale also appears to have produced more glass, evidenced by two extra smaller furnaces. These multi‑wing furnaces resemble the Lorraine‑style continental furnaces. Studies from Belgium show similar designs were common in Europe at the time.
Wood Shortage and the Switch to Coal Fuel
Between 1581 and 1584 Parliament grew concerned about dwindling wood supplies. Many industries needing high temperatures relied heavily on wood, which threatened forest resources. Laws limited wood use to landowners’ own woods. In 1609 Sir Edward Zouche received a patent to test using coal at his furnace in Winchester. By 1615 wood fuel was banned completely.
Challenges with Coal‑Fired Furnaces
Switching to coal changed many aspects of glassmaking. Coal burns with short flames, so hearths moved from the furnace’s ends to its center. Draft systems were needed for efficient heating. Some early coal furnaces, like the one at Bolsterstone, used underground flues to clear ash. Coal fumes produced carbon that clouded the glass in uncovered pots. Operators began using lids on pots, again as seen at Bolsterstone. Glass bottles from this period often turned out dark or uneven in color due to these changes.
Sir Robert Mansell’s Innovations and Success
After 1616 Sir Robert Mansell acquired Zouche’s patent and company. He launched multiple ventures, building a glasshouse close to coal sources. His goal was to cut costs and meet London’s growing demand. His Broad Street furnace made clear crystallo glass successfully. Some early attempts to establish more furnaces for London failed because transport costs were too high. Still, Mansell’s furnace in Newcastle proved a success.
Winged Furnace at Kimmeridge and Fuel Innovation
At Kimmeridge, a winged furnace was built that used local oil shale as fuel. This furnace stood out because it had deep flues and a hearth located in the center, which showed how glassmakers changed furnace design to suit a new fuel type. It was torn down in 1623 for breaching Mansell’s monopoly.
Rise of Conical Glasshouses and Chimney Designs
In the late 1600s England saw the arrival of conical glasshouses with chimneys and a new layout. These designs may have been inspired by earlier wind-powered furnaces and the round, beehive-style Venetian furnaces once used in England. The chimney made a stronger draft and whisked coal smoke away from the workspace. Some of the earliest examples were found in Bristol and Gawber in Yorkshire.
Furnace Structure and Workflow Improvements
These furnaces had underground flues and air holes that created powerful airflow to manage heat precisely. Inside, different tasks like fritting, preheating pots, and annealing glass happened in separate zones elevated above the fire. This division of labor in the furnace improved efficiency.
George Ravenscroft and the Birth of Flint Glass
Around 1663 George Ravenscroft created flint glass. This type of glass was clear and easy to shape. His first batches suffered from crizzling, a flaw that causes glass to develop tiny cracks. He fixed this by adding lead oxide. Lead glass held its shape well and resisted engraving. When Ravenscroft’s patent ran out, English glassmakers quickly adopted lead glass.
Lead Glass Sparks Industry Growth and Trade
Lead glass put England at the top of the glass world. Makers started producing large quantities of bottles for wine and phials. These were shipped abroad. One example of England’s glass trade is the Albion shipwreck near Margate in 1765. It held 11 lead glass ingots, probably bound for China. This proves lead glass was a valuable export item.
Industrial Movement in the 19th Century
In the 1800s, industry changed fast. Glassmakers started using gas fuel and continuous melting in tank furnaces. This change brought the early modern glass era to a close and began the Industrial Revolution.
Glassware Evolves with Purpose and Scale
As time passed, glassmakers began creating vessels designed for specific uses. Items like phials, goblets, drinking glasses, beakers, tankards, jugs, bottles, bowls, jars, urinals, flasks and mirror glass were now common. Mirror production and standard glassware were being made in larger volumes.
Window and Stained Glass Trends
Window glass production continued but stayed small in scale. Crown glass and broad glass (mostly green in color) dominated the 1500s. Wealthy homeowners and public buildings wanted bigger, clearer windows. Early in the period, stained glass was imported from France. After the Protestant Reformation, English churches and buildings switched to the more expensive but purer "white" glass.
