Glass is a very present element in everyday life, so much so that it becomes a complicated and long exercise to imagine being without it: no windows, no spectacles, no bottles, no street lamps, no screens for computer, mobile phone and television, no windscreen in the car, no light bulbs, no watches, just to mention a few examples. Indeed, it is a necessary material. Yet, besides its practical use, glass, e.g., in the form of lenses, mirrors, flasks, pipes or test tubes, has been fundamental in the development of scientific research and visual art, helping and guiding the human sight to look at things in different perspectives and on widely different length-scales, from the microscopic world of cells and bacteria to the open space of planets and stars.
Where and when glass first appeared is not exactly known. Naturally occurring glasses, such as obsidian, were employed in the making of arrowheads, blades and even early mirrors since the neolithic age. Obsidian was produced during volcanic eruptions by the sudden cooling down of silica-rich magma. Its manipulation was very advantageous because it could be easily fractured and the cut edge of the blades could be made very sharp. The cut edge of obsidian is theoretically one molecule thick!
The place of birth of man-made glass is usually set in the Middle East, possibly in more than one region. Clear evidence has been discovered in Egypt and in Mesopotamia, but also in the Caucasus. The date is more uncertain:
while some archaeologists date the first glass crafts back to 3500 BC, some other studies, based on the detection of glazing traces on ceramics artifacts, go back to 8000 BC. The ancient Roman historian Pliny the Elder (AD 23/24-
79) reports in his Historia Naturalis how Phoenician merchants incidentally (re)discovered glassmaking (likely ca. 2000 BC). Certainly, glass was used and diffused around 1500 BC, since many discovered glass objects date to that period. From that age on, the knowledge of glass manufacturing began to spread off in Eastern Asia and Europe.
The development of the making of glass - as of any other manufacture - is often nonlinear and not always the incidental discovery of the glass brought a civilization to work out techniques and build glass objects for practical uses in a continuous way. In some cases, like in China and Japan, for instance, the knowledge of glassmaking was acquired at some point but later forgotten and learned again or imported in later times.
Next to the core formed and the wound techniques, around 100 BC glassblowing appears: it will be a key point in the further introduction of new, lighter and transparent glass objects and the general expansion in the use of glass. Such a technique required a very fluid glass former and, therefore, temperatures much higher than in other procedures. This implied good knowledge in the construction of furnaces and ovens.
Under Romans, the diffusion of glass around the Mediterranean Sea and in Central and North Europe grew immensely. Roman glassmakers were able to produce recipients at low cost, affordable for almost everyone. They made, as well, precious refined pieces, symbols of richness and a high social status. Also the making of transparent glass, in the form of lamps, ink pots, and beverage containers was very much worked out. The main incentive to manufacture the latter was to valorize wine, allowing the appreciation of its color, besides its flavor. Windows, as well as lenses, instead, were not diffused under the Roman empire, even though glassworkers had the expertise to make them. Indeed, some instances of glass windows have, actually, been discovered in Pompeii and other places in the Italian peninsula. The making of windows spread only after the fall of the Western Roman Empire, mainly in Northern Europe, especially in churches. Stained glass windows have been recovered in the french city of Tours (5th century AD) and in England (7th century). A new impulse was given to this kind of production by Benedictine monks, whose order was founded in AD 1066. Benedictines considered the use of glass in churches as a way to glorify the Lord. In the north, probably the best examples are preserved in the Notre Dame’s cathedral in Chartres (AD 1220).
After the fall of the Western Roman Empire the most advanced region of the world for manufacturing glass remained the Middle East, in particular, the territory corresponding to present-day Syria, Egypt, Iraq and Iran, that was initially under the rule of the Sassanid Empire and then, from the 7th century on, under the influence of the Arabs and Islam. The inherited Roman techniques were further refined and the extensive trade of glass objects of Islamic making spread this knowledge very far away to Russia, Eastern Africa and China.
Arab glassmakers positively interacted with scientists, providing flasks for chemistry and particular instruments for the studies of optics. These were globes of transparent glass, filled with water, that were able to refract and
decompose light and to magnify objects. Ancient Arabs, however, did not invent lenses, even though the technology existed to produce them and, moreover, they would have been very useful in the scientific research developed at that time. The apex of the use of glass was reached between the 13th and the 14th century, after which, in correspondence with the Mongol invasions of the Middle East, glass production collapsed: in AD 1400 the Mongol invader emperor Tamerlane ordered the destruction of all laboratories in Damascus and the deportation of all glassmakers, symbolically sanctioning the end of the brilliant glass manufacture of the Middle East.
The making and use of glass recovered and grew, instead, in Europe, between AD 1100 and AD 1700, to include, besides windows, also beverage glasses, lenses, spectacles, prisms and mirrors.
The Republic of Venice was, since the 14th century, the main center for glass manufacturing. Its island of Murano jealously guarded all the most modern secrets, collected in the course of the centuries thanks to the continuous exchange of the merchants with the Middle East and further developed to yield new qualities such as, e.g., crystal
glass and multicolored glass. Very skilled glassmakers were active, as well, in Bohemia, Anvers and the Netherlands and other centers in France, Germany and, eventually, in England where the manufacture of glass was industrialized: in 1696 the number of factories amounted to 88. There, at the end of the 17th century,
George Ravenscroft invented lead glass: a combination of silica4 with potash and lead oxide. The effect of potash is to lower the melting temperature of the silica, that is otherwise around 1800 degrees Celsius. The lead oxide, instead, increases, depending on its concentration, the refractive index of the glass, and thus its luster, with respect to, e.g., the glass made in Venice. The realization of lead glass brought, in the 18th century, the construction of long-range telescopes. It is nowadays still widely used, also because of its property of shielding X-ray radiation.
In other regions of the Eurasian continent, glass diffused as well, although with a different impact on the lives of common people and on the development of technical and cultural innovation. Nevertheless, archaeological discoveries witness the use and manufacturing of glass crafts by the major civilizations of Eastern Asia: India, China and Japan. In India, glass objects were in use already around 1400 BC (discovery of Paiyampalli, Tamil Nadu), mostly consisting of beads and decorative objects. There is evidence that, in the first five centuries AD, they commonly circulated and that the knowledge of glassblowing was acquired. In ancient India, however, the applications did not evolve far beyond: glass was mainly employed to imitate other objects or gems, it was considered a surrogate material and did not have a social nor a religious role. Even in alchemy and medicine, the ravadanis - alchemical-medical chemists - preferred containers made of compressed earth or clay to glass receptacles. In China, the development of glass manufacture was at a level far lower than the one, actually quite advanced, reached in ceramics, metallurgy, printing and weaving. Glassblowing arrived in China about 500 years after its spread in the Middle East but it caused no substantial improvement in production. Glass never substituted Chinese traditional porcelain in the making of receptacles, or greaseproof paper in the fabrication of windows, to give a few typical examples. In Japan, the role played by glass until the 19th century was almost marginal, apart from certain periods. The most ancient glass artifacts discovered belong to the Yayoi era (ca. 300 BC-AD 300). With the advent of Buddhism (AD 538) the making of glass shrines propagated all over the country. Later, during the Nara era (710-794), the glassblowing technique was acquired by Japanese artisans and laboratories arose in the temples for manufacturing religious ornamental objects. Then a decline came: from the Heian era (794-1185) to the arrival of Jesuit missionaries and Western merchants at the end of the 16th century the glass industry practically disappeared. Portuguese and Dutch navigators brought to Japan lead glass and crown glass that were
adopted and commonly used, but only in the Meiji restoration (1868-1912) did a real industry of glass objects eventually start . In the rest of the world there is no strong evidence of the presence of manmade glass, but natural rock glasses such as obsidian were extensively employed. In Mesoamerica, for instance, obsidian was used to make flakes for religious offerings and household rituals, in butchery and hunting at the daily life level and, eventually, in war, in the form of swords, projectiles, axes, spears and arrowheads. Its use was common in any period and civilization, by the Mayas (classic period ca. AD 250-900), the Toltecs (ca. AD 900-1100) and
the Aztecs, who, in 1521, confronted the conquistador Cortes with obsidian weapons.
Where and when glass first appeared is not exactly known. Naturally occurring glasses, such as obsidian, were employed in the making of arrowheads, blades and even early mirrors since the neolithic age. Obsidian was produced during volcanic eruptions by the sudden cooling down of silica-rich magma. Its manipulation was very advantageous because it could be easily fractured and the cut edge of the blades could be made very sharp. The cut edge of obsidian is theoretically one molecule thick!
The place of birth of man-made glass is usually set in the Middle East, possibly in more than one region. Clear evidence has been discovered in Egypt and in Mesopotamia, but also in the Caucasus. The date is more uncertain:
while some archaeologists date the first glass crafts back to 3500 BC, some other studies, based on the detection of glazing traces on ceramics artifacts, go back to 8000 BC. The ancient Roman historian Pliny the Elder (AD 23/24-
79) reports in his Historia Naturalis how Phoenician merchants incidentally (re)discovered glassmaking (likely ca. 2000 BC). Certainly, glass was used and diffused around 1500 BC, since many discovered glass objects date to that period. From that age on, the knowledge of glass manufacturing began to spread off in Eastern Asia and Europe.
The development of the making of glass - as of any other manufacture - is often nonlinear and not always the incidental discovery of the glass brought a civilization to work out techniques and build glass objects for practical uses in a continuous way. In some cases, like in China and Japan, for instance, the knowledge of glassmaking was acquired at some point but later forgotten and learned again or imported in later times.
Next to the core formed and the wound techniques, around 100 BC glassblowing appears: it will be a key point in the further introduction of new, lighter and transparent glass objects and the general expansion in the use of glass. Such a technique required a very fluid glass former and, therefore, temperatures much higher than in other procedures. This implied good knowledge in the construction of furnaces and ovens.
Under Romans, the diffusion of glass around the Mediterranean Sea and in Central and North Europe grew immensely. Roman glassmakers were able to produce recipients at low cost, affordable for almost everyone. They made, as well, precious refined pieces, symbols of richness and a high social status. Also the making of transparent glass, in the form of lamps, ink pots, and beverage containers was very much worked out. The main incentive to manufacture the latter was to valorize wine, allowing the appreciation of its color, besides its flavor. Windows, as well as lenses, instead, were not diffused under the Roman empire, even though glassworkers had the expertise to make them. Indeed, some instances of glass windows have, actually, been discovered in Pompeii and other places in the Italian peninsula. The making of windows spread only after the fall of the Western Roman Empire, mainly in Northern Europe, especially in churches. Stained glass windows have been recovered in the french city of Tours (5th century AD) and in England (7th century). A new impulse was given to this kind of production by Benedictine monks, whose order was founded in AD 1066. Benedictines considered the use of glass in churches as a way to glorify the Lord. In the north, probably the best examples are preserved in the Notre Dame’s cathedral in Chartres (AD 1220).
After the fall of the Western Roman Empire the most advanced region of the world for manufacturing glass remained the Middle East, in particular, the territory corresponding to present-day Syria, Egypt, Iraq and Iran, that was initially under the rule of the Sassanid Empire and then, from the 7th century on, under the influence of the Arabs and Islam. The inherited Roman techniques were further refined and the extensive trade of glass objects of Islamic making spread this knowledge very far away to Russia, Eastern Africa and China.
Arab glassmakers positively interacted with scientists, providing flasks for chemistry and particular instruments for the studies of optics. These were globes of transparent glass, filled with water, that were able to refract and
decompose light and to magnify objects. Ancient Arabs, however, did not invent lenses, even though the technology existed to produce them and, moreover, they would have been very useful in the scientific research developed at that time. The apex of the use of glass was reached between the 13th and the 14th century, after which, in correspondence with the Mongol invasions of the Middle East, glass production collapsed: in AD 1400 the Mongol invader emperor Tamerlane ordered the destruction of all laboratories in Damascus and the deportation of all glassmakers, symbolically sanctioning the end of the brilliant glass manufacture of the Middle East.
The making and use of glass recovered and grew, instead, in Europe, between AD 1100 and AD 1700, to include, besides windows, also beverage glasses, lenses, spectacles, prisms and mirrors.
The Republic of Venice was, since the 14th century, the main center for glass manufacturing. Its island of Murano jealously guarded all the most modern secrets, collected in the course of the centuries thanks to the continuous exchange of the merchants with the Middle East and further developed to yield new qualities such as, e.g., crystal
glass and multicolored glass. Very skilled glassmakers were active, as well, in Bohemia, Anvers and the Netherlands and other centers in France, Germany and, eventually, in England where the manufacture of glass was industrialized: in 1696 the number of factories amounted to 88. There, at the end of the 17th century,
George Ravenscroft invented lead glass: a combination of silica4 with potash and lead oxide. The effect of potash is to lower the melting temperature of the silica, that is otherwise around 1800 degrees Celsius. The lead oxide, instead, increases, depending on its concentration, the refractive index of the glass, and thus its luster, with respect to, e.g., the glass made in Venice. The realization of lead glass brought, in the 18th century, the construction of long-range telescopes. It is nowadays still widely used, also because of its property of shielding X-ray radiation.
In other regions of the Eurasian continent, glass diffused as well, although with a different impact on the lives of common people and on the development of technical and cultural innovation. Nevertheless, archaeological discoveries witness the use and manufacturing of glass crafts by the major civilizations of Eastern Asia: India, China and Japan. In India, glass objects were in use already around 1400 BC (discovery of Paiyampalli, Tamil Nadu), mostly consisting of beads and decorative objects. There is evidence that, in the first five centuries AD, they commonly circulated and that the knowledge of glassblowing was acquired. In ancient India, however, the applications did not evolve far beyond: glass was mainly employed to imitate other objects or gems, it was considered a surrogate material and did not have a social nor a religious role. Even in alchemy and medicine, the ravadanis - alchemical-medical chemists - preferred containers made of compressed earth or clay to glass receptacles. In China, the development of glass manufacture was at a level far lower than the one, actually quite advanced, reached in ceramics, metallurgy, printing and weaving. Glassblowing arrived in China about 500 years after its spread in the Middle East but it caused no substantial improvement in production. Glass never substituted Chinese traditional porcelain in the making of receptacles, or greaseproof paper in the fabrication of windows, to give a few typical examples. In Japan, the role played by glass until the 19th century was almost marginal, apart from certain periods. The most ancient glass artifacts discovered belong to the Yayoi era (ca. 300 BC-AD 300). With the advent of Buddhism (AD 538) the making of glass shrines propagated all over the country. Later, during the Nara era (710-794), the glassblowing technique was acquired by Japanese artisans and laboratories arose in the temples for manufacturing religious ornamental objects. Then a decline came: from the Heian era (794-1185) to the arrival of Jesuit missionaries and Western merchants at the end of the 16th century the glass industry practically disappeared. Portuguese and Dutch navigators brought to Japan lead glass and crown glass that were
adopted and commonly used, but only in the Meiji restoration (1868-1912) did a real industry of glass objects eventually start . In the rest of the world there is no strong evidence of the presence of manmade glass, but natural rock glasses such as obsidian were extensively employed. In Mesoamerica, for instance, obsidian was used to make flakes for religious offerings and household rituals, in butchery and hunting at the daily life level and, eventually, in war, in the form of swords, projectiles, axes, spears and arrowheads. Its use was common in any period and civilization, by the Mayas (classic period ca. AD 250-900), the Toltecs (ca. AD 900-1100) and
the Aztecs, who, in 1521, confronted the conquistador Cortes with obsidian weapons.
Contemporary glass
”Window glass,” the archetypal glass, is the most familiar and has revolutionized architecture with each new technical innovation: from crown glass windows to the optical good quality sheets of unlimited dimensions made
of float glass, manufactured by pouring out the glass on molten tin beds, a procedure invented in 1959 by Pilkington Brothers. Other types are just as familiar: optical glasses with varying refractive indices used in lenses for reading, telescopes and cameras, container materials such as bottles and drinking glasses, or television and computer screens. Less well known forms exist such as the preservation of food by bringing it in a glassy state. Currently, communication in our daily lives heavily depends on the astounding technology embedded in silica-based fiber optics with impurity densities reaching the level of a few parts per billion range (milligrams per 1000 kilogram) and with a capability of transmitting a signal over 200 km without amplification. Window glass, existing in a myriad of types, is silica-based. Its typical chemical composition also contains calcium oxide and sodium dioxide to lower the melting point of pure silicon dioxide from about 1800 to 1300-1500 degrees Celsius. Other oxide-based glasses are manufactured such as borate, phosphate, and germanate glasses. They all have as prime requirement an oxygen coordination of the glass-forming cation of two, three or four, as postulated, more or less ad hoc, by Zachariasen in 1932.
Numerous oxygen-free glassy compounds also exist. Glasses containing elements of sulfur, selenium or tellurium, i.e., chalcogenide-based glasses, are actively researched for novel properties, as well as halide glasses, the principal one being beryllium fluoride, that is topologically equivalent to cristobalite in its crystalline form. The latter displays an attenuation one thousand times smaller than the one of silica-based optical waveguides, in the
optical length-wave range around 1500 nm, making it suitable to transmit a signal without amplification around the whole globe.
Further vitreous materials are the metallic glasses, containing no anions, that find numerous applications, especially in magnetism, because of the lack of grain boundaries. Finally, carbon-based polymer glasses constitute an important part of our daily life going by the name of nylon, polyvinyl chloride (PVC) bottles or wraps.
of float glass, manufactured by pouring out the glass on molten tin beds, a procedure invented in 1959 by Pilkington Brothers. Other types are just as familiar: optical glasses with varying refractive indices used in lenses for reading, telescopes and cameras, container materials such as bottles and drinking glasses, or television and computer screens. Less well known forms exist such as the preservation of food by bringing it in a glassy state. Currently, communication in our daily lives heavily depends on the astounding technology embedded in silica-based fiber optics with impurity densities reaching the level of a few parts per billion range (milligrams per 1000 kilogram) and with a capability of transmitting a signal over 200 km without amplification. Window glass, existing in a myriad of types, is silica-based. Its typical chemical composition also contains calcium oxide and sodium dioxide to lower the melting point of pure silicon dioxide from about 1800 to 1300-1500 degrees Celsius. Other oxide-based glasses are manufactured such as borate, phosphate, and germanate glasses. They all have as prime requirement an oxygen coordination of the glass-forming cation of two, three or four, as postulated, more or less ad hoc, by Zachariasen in 1932.
Numerous oxygen-free glassy compounds also exist. Glasses containing elements of sulfur, selenium or tellurium, i.e., chalcogenide-based glasses, are actively researched for novel properties, as well as halide glasses, the principal one being beryllium fluoride, that is topologically equivalent to cristobalite in its crystalline form. The latter displays an attenuation one thousand times smaller than the one of silica-based optical waveguides, in the
optical length-wave range around 1500 nm, making it suitable to transmit a signal without amplification around the whole globe.
Further vitreous materials are the metallic glasses, containing no anions, that find numerous applications, especially in magnetism, because of the lack of grain boundaries. Finally, carbon-based polymer glasses constitute an important part of our daily life going by the name of nylon, polyvinyl chloride (PVC) bottles or wraps.
References:
This text is freely taken and adapted from Leuzzi & Nieuwenhuizen (2008).
For a fascinating account of the role of glass in science development, see the book of Macfarlane & Martin (2002).
For the history of glasses in India see Sen & Chaudhary (1985) and Subbrarayappa (1999).
I took information from the historical development and use of glass in Japan from Blair (1973).
This text is freely taken and adapted from Leuzzi & Nieuwenhuizen (2008).
For a fascinating account of the role of glass in science development, see the book of Macfarlane & Martin (2002).
For the history of glasses in India see Sen & Chaudhary (1985) and Subbrarayappa (1999).
I took information from the historical development and use of glass in Japan from Blair (1973).