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It began as a rare luxury, valued alongside precious stones and guarded by skilled craftsmen.
Over thousands of years, it transformed architecture, science, art, and medicine.
It allowed people to see farther into space, deeper into the microscopic world, and eventually transmit information around the planet at the speed of light.
Yet, at its core, it is just a deceptively simple mixture of sand, minerals, and heat.
Learn more about the history of glass on this episode of Everything Everywhere Daily.
Glass is one of humanity’s oldest synthetic materials and one of its most important. It began as a rare substance used to imitate gemstones and eventually became an ordinary material for windows, bottles, mirrors, lenses, and many other applications.
Its history is closely tied to advances in chemistry, furnace design, manufacturing, and trade.
Before we get into the history of glass, we should address the very important question: what is glass?
Glass is an amorphous solid, meaning its atoms are arranged irregularly rather than in the repeating crystal structure found in minerals such as quartz. Most common glass is made primarily from three ingredients:
Silica, which is usually obtained from sand, and forms the basic structure.
Soda, traditionally derived from mineral natron or plant ashes, which lowers the temperature at which silica melts.
And Lime, which is usually derived from limestone, and makes the finished glass more chemically stable and resistant to water.
Pure silica melts at approximately 1,700°C, or 3,092F far beyond the capabilities of most ancient furnaces. Adding soda made glass production possible at lower temperatures, while lime prevented the resulting material from slowly dissolving or deteriorating.
Here I should address that urban myth that glass is actually a very, very slow-flowing liquid. This is not true. Glass is a solid, as anyone who has cut themselves on it can attest.
The reason for the glass-is-a-liquid myth was that, in very old stained glass windows, the glass was thicker at the bottom than at the top. Some took this as evidence that glass was slowly flowing over time. In reality, it was an artifact of the production methods of the time, resulting in uneven glass thickness. The thicker parts were put at the bottom for stability.
While most glass we are familiar with was manufactured, glass can also form naturally. Obsidian is volcanic glass created when lava cools too quickly to crystallize. Lightning strikes can fuse sand into branching glass structures called fulgurites. Meteorite impacts can also produce natural glass.
Obsidian was one of the most valuable materials of the Stone Age. Because it fractures into extremely sharp edges, prehistoric people used it to make knives, scrapers, spear points, and arrowheads.
The precise origin of glassmaking remains uncertain. Early glass probably emerged gradually from experiments with ceramic glazes and metalworking slag rather than from a single dramatic invention.
Small glass beads and accidental glassy materials appeared in Mesopotamia and Egypt during the third millennium BC. Large-scale, deliberate production developed around the middle of the second millennium BC, probably in northern Mesopotamia, Syria, and Egypt. Evidence suggests that glass vessels were being manufactured by approximately the sixteenth or fifteenth century BC.
The traditional story told by the Roman writer Pliny the Elder claimed that Phoenician sailors accidentally discovered glass when blocks of soda used to support cooking pots fused with beach sand.
The story is almost certainly a legend. The temperatures of an ordinary cooking fire would have been insufficient to produce useful glass, and archaeological evidence indicates a much more gradual technological development.
Early glass was seldom clear. It was usually opaque or translucent and colored blue, green, turquoise, red, yellow, or white. Deep blue glass was especially prized because it resembled lapis lazuli, a valuable stone imported from Afghanistan. Ancient descriptions sometimes treated glass as a kind of artificial or flowing stone.
Glassmaking was an elite craft. Furnaces were difficult to operate, raw materials had to be carefully selected, and colored glass required specialized knowledge. Cobalt produced blue glass, copper could produce blue, green, or red, manganese could produce purple, and antimony compounds were used for opaque white or yellow glass.
During the first millennium BC, glassmaking revived across the eastern Mediterranean after the Bronze Age collapse. Glass beads and vessels circulated through Phoenician, Greek, Persian, Etruscan, and other trading networks.
Most glass objects remained relatively expensive. Techniques included casting, core-forming, cutting, grinding, mosaic work, and pressing glass into molds.
Greek craftsmen became increasingly skilled at producing bowls by casting glass into molds and then cutting or polishing the surfaces. Some vessels imitated carved stone, metalwork, or precious gemstones.
One of the most famous glass objects in the ancient world was the coffin of Alexander the Great, made after the original gold coffin was melted down.
Glass was probably not independently discovered in China. Glass was an imported luxury material during the late second or early first millennium BC. The earliest securely identified glass objects in China date mainly from the Warring States period, roughly 475 to 221 BC, including beads and small ornaments influenced by West and Central Asian glassmaking
Imported Roman and later Sasanian glass became more common during the Han dynasty and the centuries that followed, arriving via the Silk Road and maritime trade. Large-scale vessel glassmaking, however, never became as important to Chinese culture as ceramics or porcelain.
The major advance in ancient glass production was the development of glassblowing.
Glassblowing probably developed in the Levant during the first century BC. At some point, a craftsman gathered molten glass on the end of a hollow iron blowpipe and inflated it by blowing through the tube.
This transformed the industry.
Earlier glass products required laborious casting, core-forming, grinding, and polishing. A skilled glassblower could create a hollow vessel in minutes. Glass could be blown freely, inflated inside a mold, stretched into a tube, decorated, or shaped with simple hand tools.
The technique spread rapidly through the Roman world during the first century.
The Romans did not invent glass, but they turned it into a widely available commodity.
Large furnaces in Egypt and the eastern Mediterranean produced substantial blocks or slabs of raw glass, which were then transported to secondary workshops throughout the empire. There, glassworkers remelted and shaped the material into glass objects.
Roman glass included drinking cups, perfume bottles, jugs, bowls, jewelry, and many other creations. Glass containers became especially useful because they did not absorb smells or flavors as readily as pottery.
The Romans produced both colored and nearly colorless glass. Iron impurities naturally gave glass a blue-green tint. Adding substances such as manganese could neutralize some of the color, although ancient glass was rarely as perfectly clear as modern glass.
The Romans were also the first people to use glass in windows. Early window glass was often cast or rolled into relatively small, thick sheets. It tended to be uneven, cloudy, and distorted.
Window glass remained expensive, but it allowed architects to admit light while keeping out wind, rain, and cold. This was especially valuable in baths, where large interior spaces had to remain warm.
The collapse of the western Roman Empire did not end glassmaking, but it fragmented the industry. Workshops continued in the Byzantine Empire, the Islamic world, western Europe, and parts of Asia.
The Byzantine Empire preserved many Roman techniques, including blowing, molding, cutting, and mosaic production.
After the Islamic conquests of the seventh century, glassmaking flourished in Syria, Egypt, Mesopotamia, Persia, and other regions. Islamic glassmakers inherited Roman and Byzantine traditions but developed distinctive decorative methods.
Glass reached South Asia in antiquity through both local experimentation and international trade. Indian craftsmen became especially skilled at producing beads, bangles, decorative glass, and small vessels. South Asian glass circulated through Indian Ocean trade networks into Southeast Asia and East Africa.
In medieval Europe, glass was produced in forested regions where wood supplied both furnace fuel and ash. These workshops made bottles, drinking vessels, beads, and window glass.
Most medieval household glass, known as forest glass, was greenish because of impurities in the raw materials.
The great medieval contribution to architectural glass was the stained-glass window.
Colored glass had existed since antiquity, but medieval church builders combined pieces of colored glass into large narrative and symbolic compositions. Individual pieces were fitted into lead strips called cames, joined together, and supported by iron frameworks.
Details such as faces, folds, and inscriptions could be painted onto the glass with pigments and then fired.
Romanesque and Gothic churches used stained glass to fill interiors with colored light. The expansion of Gothic architecture in the twelfth and thirteenth centuries, with pointed arches, ribbed vaults, and flying buttresses, allowed walls to contain much larger windows.
Venice emerged as Europe’s leading center of luxury glassmaking during the late Middle Ages and Renaissance.
Venetian glassmakers benefited from commercial links with the Byzantine and Islamic worlds, access to imported raw materials, and a wealthy market for luxury goods. In 1291, Venetian authorities ordered that glass furnaces be moved to the nearby island of Murano to prevent fires.
From approximately 1500 to the early eighteenth century, Venice was Europe’s dominant supplier of fine luxury glass. The Venetian government attempted to protect technical knowledge by restricting glassworkers’ movements, but many craftsmen emigrated and established Venetian-style production elsewhere.
The scientific revolution depended heavily on improved glass.
Lenses had been used as magnifying devices in the Middle Ages, and eyeglasses appeared in Italy by the late thirteenth century. Early spectacles corrected farsightedness using convex lenses. Concave lenses for nearsightedness followed.
The telescope appeared in the Netherlands around 1608. Galileo improved the instrument and used it to observe mountains on the Moon, Jupiter’s moons, and the phases of Venus.
The compound microscope developed around the same period. Robert Hooke used microscopes to examine insects, plants, and other materials, while Antonie van Leeuwenhoek’s carefully made single-lens microscopes revealed microorganisms.
These discoveries depended on the ability to produce glass that was reasonably clear, homogeneous, and accurately shaped.
English glassmaker George Ravenscroft patented an improved lead glass in 1674. By adding lead oxide, manufacturers produced glass with a high refractive index, notable brilliance, and a characteristic ringing sound.
The Industrial Revolution transformed glass from a skilled workshop product into a major industrial material.
Coal-fired furnaces provided more consistent heat than wood. Steam power operated grinding, cutting, and polishing machinery. Improved transportation made it easier to move sand, limestone, coal, finished bottles, and window glass.
Chemists gained better control over composition. The Leblanc process, developed in the late eighteenth century, created soda ash from salt and helped replace limited natural supplies of natron and plant ash. The Solvay process, developed during the nineteenth century, provided a cleaner and more economical source of sodium carbonate.
Mechanical pressing appeared in the early nineteenth century. A measured amount of molten glass was placed in a mold and pressed into shape with a plunger.
Pressed glass allowed manufacturers to mass-produce bowls, dishes, and decorative objects that resembled expensive cut glass. It brought ornamental glassware within reach of middle-class and working-class consumers.
Early plate glass was made by casting molten glass onto a metal table, rolling it flat, then grinding and polishing both sides. The process produced high-quality panes but was slow, wasteful, and expensive.
Industrial plate glass nevertheless made possible the great display windows of nineteenth-century department stores and exhibition buildings. The Crystal Palace, constructed for London’s Great Exhibition of 1851, demonstrated the architectural potential of prefabricated iron and glass.
Michael Owens developed a commercially successful automatic bottle-making machine in the early twentieth century. Automatic machines could produce bottles much faster and more consistently than teams of glassblowers.
Cheap bottles transformed beverages, medicine, and food preservation. Standardized bottles also encouraged branding, labeling, and mass distribution.
The most important modern development in flat-glass production was the float process.
Sir Alastair Pilkington and Kenneth Bickerstaff developed the commercially successful method in Britain during the 1950s. Molten glass flows continuously from a furnace onto a bath of molten tin. Because glass is lighter than tin and does not readily mix with it, it floats and spreads into a smooth ribbon.
Gravity and surface tension create surfaces that are naturally flat and parallel. Float glass eliminated much of the grinding and polishing required by earlier plate-glass methods. It made large, clear, distortion-free panes economical on an enormous scale.
Today, glass can be found almost everywhere. Durable, scratch-resistant glass is in your smartphones; glass fiber-optic cables are the backbone of the internet; and glass is a fundamental part of almost every home.
There is a lot more to be said about glass, but it has had a remarkable journey for something that was probably discovered by accident thousands of years ago.