Let There Be Light (And A View)
The evolution of historical windows
There’s a considerable amount of information on glass innovation but there isn’t much on how windows evolved with glass technology. Sites often confuse function (casement, sash etc) with architectural styles (Gothic, Georgian etc.) and with the design (oriel, bay, lancet etc.) of the window.
Le Corbusier once said, 'The history of architecture is the history of the struggle for light.' No other architectural component wields as much influence over a building's appearance, character, and space as the window. Throughout history, advancements in glass technology have influenced the design of windows to maximize light, views, ventilation, and minimize drafts.
Early windows used a myriad of coverings.
In ancient times, windows often lacked glass and instead relied on various materials including paper, animal hide, horn, cloth and wood shutters to cover the openings. It wasn't until around 1550 BC in Egypt, approximately 4000 years ago, that glass was first produced.1
About 100 AD, the Romans were the first to use glass for architecture. The glass had a greenish-blue color with a pebbly texture and panes were set into heavily partitioned wooden frames. However, following the decline of the Roman Empire, the knowledge of window glass production was lost. Subsequently, many structures resorted to using alternatives like paper, cloth, horn, alabaster, or eventually shutters to cover their openings.
The invention of broad glass led to the development of medieval mullioned windows
In the 11th century, the Germans made sheet glass called broad glass, but it was mostly opaque with a green tint and provided a distorted view. In the 1200s, following the Norman Conquest, sheet glass arrived in England. But only the very wealthy could afford glass, and their homes had windows with mullions made of timber or stone. In the homes of common people, thin sheets of animal horn were used. During a period of extensive church construction in the 11th and 12th centuries, stained glass was first used in churches. The earliest surviving stained glass can be observed in Augsburg Cathedral, located in Augsburg, Germany.
Although mullioned windows—vertical components that are located between a window's two framed sides—have been around since antiquity, they made their first appearances in Gothic architecture. Incorporating windows into structures often presented structural difficulties. Window openings in stone walls often weakened the structure since the windows could not support the weight of the walls. Horizontal supports such as lintels and arches, were designed to take the weight off the walls. However, lintels and arches also needed support so mullions were used. Various styles of windows developed as a result but here are some prominent ones:
Lancet and rose
The lancet window originally emerged in England during the early French Gothic era (c. 1140–1200). The rose window was derived from an oculus, a small, round ancient Roman window.
Oriel
During the medieval period, around the 15th century,2 the precursor to the bay window, the oriel window appeared.
Cross
During the High Renaissance in Europe, window openings conformed to classical proportions. They were often divided by a single mullion and a single transom, forming a cross, with smaller glass panes fitted between leaded mullions to create intricately patterned windows.
Venetian
The Venetian window is a large tripartite window consists of an arched central light, symmetrically flanked by two shorter window lights.
Advancements in glass technology gave rise to the casement window.
By the 15th century, casements were replacing solid shutters and older styles of mullioned windows. Rectangular openings with frames made of iron became the standard in all buildings. At the same time, Tudor prosperity (1485 -1603) meant mullioned windows now had larger panes of glass. More homes could afford windows but they were still small and came in narrow shapes with a criss-cross lattice pattern. These windows opened outward to let in air, marking the introduction of the first operable windows.
Crown glass greatly improved the view through windows.
Crown glass, the first flat and smooth glass was created in France in the 1320s but was not produced in England until the late 1600s. It was clearer and finer than broad glass and often assembled using lead strips reinforced with steel since lead was soft. Crown glass was an expensive luxury, so only churches and palaces used it. Crown glass has a characteristic bull’s-eye where the pipe was used to blow the glass. The borders were significantly thinner than the center due to this technique, resulting in uneven glass thickness. Glassmakers usually reserved the center areas for less expensive windows.
Sash windows brought an elegant, streamlined form that increased interior light.
During the 17th century, windows were introduced to America from Europe. Shortly after the first sash window was created in Europe. The larger panes made them only affordable to the wealthy. The sash's thin frame and sizable glass portions give it a delicate aesthetic. They don’t take up space and they complement the facade rather than detracting from it. Initially, just the upper half of the window had sashes installed, leaving the lower part of the window still covered by shutters.
The earliest sash windows were Georgian sash windows that traditionally had 6 panes over 6 configuration but later there were many different designs. In the 17th century, England produced two new kinds of sash windows which are the double-hung and the vertical sliding window.
By throwing blown glass into a furnace and rolling it out, a technique known as cylinder glass was invented in Europe in the late 1700s. With the introduction of this method, larger and smooth panes became more widely available and more inexpensive. The industrial revolution's exponential increase in production made it possible to build the cast iron and plate glass Crystal Palace for the Great Exhibition of 1851.
The production of plate glass began in England in the 1830s after it was created in France in the 17th century. For the first time, molten glass was cast onto a plate instead of being hand-blown, and it was then polished and ground. While there were still distortions, there were fewer ripples than in prior glass. Crown glass, earlier varieties of blown glass and plate glass were the most common forms of glass used in sash windows.
The affordability of sash windows led to a variety of designs.
Sash windows became standard in Europe and the United States during the 18th and 19th Centuries. The windows were now more affordable, constructed primarily from Baltic Pine, with thinner glass and saw a gradual reduction in the width of glazing bars. Sashes were now more common than casements and painted sashes in green, black and brown were popular. The late 1800s also marked a time of rapid change in architectural styles resulting in many different sash window designs.
Mechanical glass enabled significant advancements in glass innovation.
Early in the 20th century, machine-made glass began to replace hand-blown glass. American glassmakers created the first mechanical technique for producing machine-drawn cylinder glass in 1903. Laminated glass, a type of safety glass, was also developed in the same year. Due to its stability when broken, it allowed for the creation of larger panes.
At the start of the 20th century, flat glass could still not be mass-produced. Cylinder glass could be mechanically drawn, but the glass still needed to be manually flattened. Emile Fourcault, a glassmaker from Belgium, created a device in 1901 that could draw a sheet of glass five floors straight up from a vat of molten glass. Because it was drawn out of the furnace, it was known as drawn sheet glass. Large sheets could now be produced more easily, but the method left surface marks.
Sir Alastair Pilkington created the float glass manufacturing process in the late 1950s, which is still used for making 90% of the sheet glass today. Float glass is high-quality glass that reflects light like a mirror without any waves or distortions.
Historical glass and windows
Understanding types of glass and materials can help date historical windows for period homes (see Repository). Window glass manufactured before the 1950s is typically considered historical or antique. The most prevalent types of historical glass in the 19th and 20th centuries were wavy glass (c 1870-1930) and bullseye glass. Since there are still striations from when the glass was lifted, you can still see a waviness in the glass. Glass made before 1850 typically has bubbles and defects and is thick. Old beveled glass was also hand-cut and reflected light in a variety of ways. Modern glass from the 20th century is thinner and typically flawless, though beveled glass has to have a slight thickness.
The architectural style can help you determine the correct type of window and glass. Tudor-style houses frequently have latticed, mullioned windows. Sash windows can vary based on the era, but the Georgian, Italianate, and Victorian styles are the most prevalent. Casement windows were common in post-Victorian and Edwardian architecture. Period glass maintains architectural integrity and allows buildings to be experienced as intended.
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Queen’s Repository
Historic Glass Sources
USA
Addams: Stained Glass (CA)
Artisan Glass Works (MD)
Bendheim Restoration (NJ)
Hollander Historic (TX)
Lancaster Paint & Glass (PA)
Seventy Restoration: Stained and leaded glass (MI)
Schott Historic Glass (NY)
UK
Hereford Glass (Hereford)
Heritage Glass and Glazing (London)
Histoglass (North Yorkshire)
London Crown Glass Company (Oxfordshire)
Richard Cann: British leaded lights and stained glass
Glossary
Alabaster
Alabaster is a translucent type of gypsum that has been used for centuries for statuary, carvings, and other ornaments. Alabaster can be white, yellow, pink, brown etc. It can be dyed easily.
Bay, bow and oriel windows
A bay window is a multi-panel window, with at least three panels set at different angles to create a protrusion from the wall line. An oriel window is type of bay wind that projects from upper stories whereas bay windows start at the lowest floor and may continue upwards. Bow windows can be oriels or bays but they have a curved shape.
Casement window
A metal or timber window in which the opening lights are hung on hinges. They can open out or inwards.
Hung window
A window consisting of vertically sliding sash which utilize counterbalancing devices to allow the sash to be opened to any position between open and closed. A vertical sliding window is a hung or non-hung window that has at least one manually operated sash that slides up and down within a common frame.
Light or window light
A light is a pane of glass or a section of glass inside a window frame.
Mullion
A slender pier forming the division between the lights of a window.
Period home
A period home is one that was built during a specific time that was characterized by a distinctive architectural style. It usually refers to an era before World War I.
Sash
A sash is a frame for holding the glass in a window and capable of being raised and lowered in vertical grooves.
https://web.archive.org/web/20110415194738/http://www.glassonline.com/infoserv/history.htm
For context the middle ages ended with the fall of Constantinople in 1453 AD