From the stained glass windows of medieval churches to the famous mirrors of Renaissance Venice, flat glass has provided us with protection from the environment while reflecting the beauty of nature. It offers year-round comfort, reduces energy costs, enhances safety, and replaces brick and mortar walls with a panoramic view of light and natural beauty.
The History of Glass
The first glass was a mineral called obsidian, created naturally during volcanic eruptions. Glass was produced around 1500 BC in Egypt and Mesopotamia. These ancient cultures crafted glass objects using rudimentary casting methods. The earliest glassmakers shaped glass by applying molten glass around a core made of sand or clay, then removing the core material. Finally, the cooled glass was cut and polished.
In the following millennium, glass production became more widespread in the ancient world, with several improvements in basic glass-making techniques, such as cutting. Glassmakers learned to add certain components to enhance durability, increase clarity, or create special colors. However, glass production remained labor-intensive, and glass was mainly used in royal contexts for religious ceremonies.
The glass industry witnessed its first revolution around 300 BC when Syrian glassblowers invented the blowpipe, enabling the creation of countless products with varying shapes and thicknesses. Shortly after the invention of the blowpipe, the two-part mold emerged, allowing glassmakers to produce identical glass objects in large quantities. These two inventions made glass products more affordable for ordinary people.
In the first century AD, the Romans revolutionized glassmaking by employing various methods such as glassblowing, molding, and pressing to mass-produce differently shaped glass products for decoration. Window glass, produced by pouring and stretching molten glass on a steel table, transformed architectural aesthetics. The Roman Empire also produced flat glass by blowing large glass spheres or cylinders, which were then separated and flattened. They began creating mirrors by coating flat glass with a silver amalgam, a Roman innovation that quickly spread throughout Europe.
With the fall of the Roman Empire, many glassmaking techniques were lost. In Western Europe, glass became a luxury product, and flat glass was used for the windows of medieval churches. However, Byzantine glassmaking continued to innovate. Around 650 AD, Syrian glassmakers developed a revolutionary glass technology to produce “crown” glass. This type of glass was created by making a hole in a hot glass sphere and then spinning the soft glass to form a thin, round pane with a distinctive “bulls-eye” at the center. Because this glass was relatively inexpensive, it remained in use for windows until the late 19th century.
Venetians imported glassware from Byzantium and began their prosperous glass industry in the 13th century. To protect their “trade secrets”, glass furnaces were moved to Murano Island, where the Italian glassmaking Renaissance continued for centuries. Venetians perfected the technology for producing flat glass by casting colorless glass on a steel table and polishing the glass until it was perfectly smooth. They also developed the mercury coating method to create mirrors that became famous throughout Europe. Despite the many lives lost due to mercury poisoning, the profitability of mirrors led to severe penalties, including the death penalty for those who revealed manufacturing secrets. Nonetheless, Venetian glassmaking expertise spread across Europe. Soon after, French glassmakers improved Italian technology with larger tables for producing larger glass panes and developed annealing ovens to cool glass over several days. Glassmaking also advanced in Germany, Northern Bohemia, and England, where George Ravenscroft invented lead glass in the 1670s. Around this time, flat glass was also produced in France using the cylinder method. To improve upon Roman technology, French artisans blew long cylindrical glass, separated it, and flattened it with wooden blocks to create rectangular sheets.
With the establishment of the English flat glass company in 1773, England became the center of high-quality window glass production worldwide. This marked the first time in the history of the glass industry that window glass became affordable for most homeowners.
England was the first country to seek and establish its glass manufacturing centers in its American colonies. They feared competition from domestic producers and illegal glass furnaces in America. After the American Revolution, glassmaking techniques spread from Europe, leading to a vibrant glass industry in the United States. The first innovation by American producers was the invention of the pressing machine, patented in 1825. During the pressing process, molten glass was poured into a mold and pressed into the desired shape using a piston.
The Industrial Revolution brought a series of innovations in glass manufacturing, beginning with the introduction of the pneumatic pump in England in 1859. This pump automated the glassblowing process, reducing the need for skilled craftsmen. Advances in chemistry also significantly impacted glass production, allowing manufacturers to alter raw material compositions to create more durable and heat-resistant products. In 1871, William Pilkington invented a machine for the automated production of flat glass using the cylinder method. This mechanization was further improved by J.H. Lubber in the United States in 1903.
Entering the next century, glass manufacturers recognized that flat glass could be tempered by reheating and cooling it quickly. Thanks to the unique stresses of glass materials, the strength of the glass increased by about 400%. This was particularly important for the burgeoning automotive industry.
The cylinder technology became outdated when Irving Colburn (USA) and Emile Fourcault (Belgium) jointly developed a new technology to draw molten glass from the furnace in a thin stream, forming flat glass and cooling it through drawing the glass ribbon between two asbestos rollers. Although the glass produced by the “drawing” method still had some waviness, it was the highest quality flat glass to date and reduced production costs. In the 1920s and 1930s, as “drawn” glass dominated the market, the price of flat glass dropped by over 60%.
The drawing technology also allowed for the production of patterned glass by drawing glass ribbon between printed asbestos rollers. Architects and builders quickly incorporated patterned glass into various applications requiring privacy.
In the years following World War I, the flat glass industry experienced remarkable growth due to a housing boom and the automotive industry. By 1929, 70% of flat glass produced in the U.S. was sold to the automotive manufacturing sector. Much of this was safety glass, produced by laminating two sheets of glass with an intermediate layer of cellulosic acetate.
Despite advancements in production technology, the polishing process to create high-quality flat glass remained time-consuming and costly.
Glass manufacturers worldwide sought ways to produce high-quality polished flat glass without additional finishing processes.
The glass production industry underwent a complete transformation when Alastair Pilkington invented modern float glass technology in the 1960s, minimizing differences compared to polished glass. In Pilkington’s technology, a narrow stream of molten glass continuously flows into a shallow bath of molten metal, typically tin. The molten glass spreads on the surface of the molten metal, producing high-quality glass ribbon with stable thickness and thermally polished. Pilkington’s technology revolutionized the global glass industry in many ways. It significantly reduced the cost of flat glass, created new applications for flat glass products such as interior decoration and skyscraper construction. With lower costs, high-quality glass began to dominate the construction, automotive, and mirror industries. Today, over 90% of the world’s flat glass production is made using Pilkington’s technology.
Modern Developments in the Glass Industry
In the 1960s, companies holding patents for float glass technology, particularly Pilkington, significantly enhanced their productivity and reduced glass prices. This caused difficulties for companies lacking float glass technology. By 1975, float glass production lines accounted for up to 97% of glass manufacturing worldwide, affirming that Pilkington’s technology is one of the greatest inventions in the history of the glass industry.
Float glass technology has led to the emergence of many new technologies and glass products. For the first time, high-quality sheet glass was produced in various thicknesses ranging from 0.5 to 19 mm or more. Thicker glass was made for safety and soundproofing purposes, while still meeting aesthetic standards. Additionally, this technology allowed manufacturers to alter the raw material composition to create new products, including colored glass.
Due to the global energy crisis in the early 1970s, the demand for sheet glass declined, impacting the entire industry. For energy efficiency reasons, less glass was used in high-rise buildings. The residential construction industry was on the brink due to a severe economic downturn. Compact cars utilized less glass, and to worsen the situation, Ford Motor Company began producing float glass for their own needs, significantly reducing the amount sold to the automotive sector. In fact, in 1970, Ford’s Nashville plant was the largest float glass manufacturer in the world.
With many new technologies, the glass industry has responded to the growing demand related to energy efficiency and new properties. For example, through research in light energy, manufacturers developed coatings that allowed glass to absorb sunlight and thermal radiation more efficiently, or sunlight control coatings that could block solar heat in hot climates while still allowing light to pass through. In 1970, low-iron glass for solar panels was introduced, enhancing sunlight transmission to convert thermal energy into electrical energy.
Moreover, manufacturers began to introduce high and medium-level reflective coatings, enabling architects and builders to achieve exceptional performance in light transmission, sunlight reflection, and shading efficiency. High-reflective glass products created through vacuum deposition, along with medium-reflective glass coated via pyrolysis, initiated a revolution in architecture in the late 1970s and early 1980s, leading to the construction of striking buildings with energy efficiency that we see today.
Also in the 1970s, new demands were placed on the automotive industry, presenting numerous challenges. Manufacturers produced more flexible laminated glass, laying the foundation for the automotive industry to design new, more aerodynamic shapes. Additionally, safety glass, first manufactured for cars in the 1920s, became thinner, lighter, and easier to shape.
With the improvement of the global economy in the early 1980s, glass manufacturers continued to strive for new technologies to optimize the energy efficiency of glass windows. Undoubtedly, reflective glass has been the most significant success of the glass industry in recent decades. In winter, the glass can leverage its ability to absorb light energy while reflecting heat from heaters back into the room. By increasing the temperature of the glass, condensation levels can be minimized. These revolutionary products are increasingly establishing their presence in the glass market. In fact, reflective glass products have increased by 13% since 1990.
Alongside the development of energy-efficient technologies, attention has also turned to the window fabrication industry. The rise of vinyl windows or those containing argon gas has created new demands for fabrication equipment. One of the cutting-edge technologies of the late 1980s was the spacer system.
In the field of soundproofing, new window designs have been created for homes located in noisy areas. For example, some manufacturers in Europe have combined glass panels of varying thicknesses to filter different sound frequencies, while others have added laminated glass to reduce noise pollution.
Nguyễn Thành – PKT TCT – Translated from Glass Journal
