Glass that is put into buildings or automobiles, in windows or table tops is usually called flat-, float-, window or plate glass. So exactly what is glass? The ancient Romans made flat glass by rolling out hot glass on a smooth surface. The resulting glass was neither clear nor even, but it was good enough to use in windows of the day.
In fact, glass was quite a luxury at the time and only the nobility could afford it. This plate glass was then ground and polished on both sides. By the late s, glass was being made by blowing a very large cylinder and allowing it to cool before it was cut with a diamond. After being reheated in a special oven, it was flattened and affixed to piece of polished glass which preserved its surface. In , a gentleman named William Pilkington invented a machine that allowed larger sheets of glass to be made.
It was the first of a number of marvelous glass-related inventions to come from the Pilkington family. Glass is one of the most versatile—and misunderstood—materials in the world. In fact, lots of materials called glass are actually ceramics and have an entirely different manufacturing process. Here, we discuss glass that is put into buildings and vehicles, which is glass made by the float process. That is why it is generally called float glass. The ancient Romans made glass by blowing air through a very large cylinder and allowing it to cool, then cutting it with a diamond.
The resulting glass was neither clear nor even, but it was good enough to be used in windows of the day. This glass was then ground and polished on both sides. By the late s, new additives were mixed in. In , William Pilkington invented a machine that allowed larger sheets of glass to be made. It was the first of many ingenious glass-related inventions to come from the Pilkington family.
By the early s most glass was manufactured using the sheet glass method—through which a ribbon of glass was drawn from a tank furnace between cooled rollers. It produced a less expensive, albeit imperfect window.
Manufacturing processes did not change much until when another Pilkington by the name of Sir Alistar invented the float glass process. It changed glass manufacturing forever. In the float glass process, a continuous strip of molten glass at approximately degrees centigrade is poured continuously from the furnace onto a large shallow bath of molten metal, usually tin.
For example, the Romans created a fourth-century goblet known as the Lycurgus cup , which appears jade green when lit from the front but blood red when backlit. During medieval times, the secrets of glassmaking were kept alive in pockets of Europe and the Arab world. By the High Middle Ages, Europeans were producing stained glass.
These magnificent paintings-on-glass, in churches in Western Europe, played a huge role in teaching the mostly illiterate masses church catechism, Wight says. Though windows had been around since Roman times, they remained expensive and hard to come by.
But that began to change after the building of the Crystal Palace for the Great Exhibition, a massive structure completed in London containing nearly 1 million square feet of glass. The Crystal Palace showed people the power and beauty of windows, and had an important influence on architecture and consumer demand down the road, says Alan McLenaghan , the CEO of SageGlass, a company that makes tinted windows and other products.
The Crystal Palace burned to the ground in , but windows became much more affordable some years later, when the British glass company Pilkington invented the float-glass technique , a simple way of creating flat planes of glass by floating them atop molten tin.
Long before windows become commonplace, unknown inventors in northern Italy created the first spectacles at the end of the 13th century. The invention helped spread literacy and paved the way for more advanced lenses, which would enable humans to see unfathomable things.
Nearby, by the s, Venetians began perfecting the process of making cristallo , a very clear glass, borrowing techniques developed in the Middle East and Asia Minor. One recipe involved melting carefully selected quartz pebbles with purified ashes from salt-loving plants, which, unknown at the time, supplied the right ratio of silica, manganese, and sodium.
Secrecy was a matter of life and death; glassmakers, though they enjoyed a high social status, faced execution if they left the Venetian Republic. The Venetians dominated the glass market for the next years. The Venetians also created the first mirrors made of manufactured glass, which would change the world in untold ways.
The invention paved the way for telescopes and revolutionized art, allowing the Italian painter Filippo Brunelleschi to discover the linear perspective in They also changed the conception of the self. Besides reflection, glass allowed for magnification. Around , the father-son team Hans and Zacharias Janssen invented a compound microscope, with lenses at two ends of a tube, producing a nine-power enlargement.
A Dutchman, Antony van Leeuwenhoek , made another leap forward. A relatively uneducated apprentice in a dry-goods store, where he counted threads in cloth using magnifying glasses, he developed new ways of polishing and grinding lenses, creating a device that allowed him to magnify images up to times. After the collapse of the great empires of the Late Bronze Age, there was a lengthy gap in glass production in both Mesopotamia and Egypt.
No firm evidence has yet been found to prove that glass was being produced during the Early Iron Age. Although it does not disappear completely from the archaeological record, glass is extremely rare in the period between the twelfth and eighth centuries B.
But this is not to say that glass was completely unknown. Literary evidence for glass-making has been found both in Middle Babylonian cuneiform texts and in Neo-Assyrian tablets from Nineveh.
It is assumed that these texts offer a thread of continuity stretching across the four-century gap in the archaeological record. Early glass objects, too, were kept as precious keepsakes and heirlooms during this period, as is shown by the finds of mosaic glass in the citadel at Hasanlu, which was destroyed in the late ninth century B. When glass-making does re-emerge, the products appear in a variety of new forms and with different functions and techniques.
Very little remains, however, to indicate the presence of early glass factories in Mesopotamia or elsewhere in western Asia. A fragment of an opaque turquoise blue 'segmental' glass ingot was found in the N. Palace at Nimrud and seems to date from the seventh century BC, but other ingots from Nimrud, in opaque red glass, are probably not earlier than the Achaemenid period.
The earliest use of glass on a large scale in the first millennium BC occurred on Phoenician ivories. The glass was used as an inlay for embellishing and accentuating details of figures and floral designs and gave the ivory a polychrome appearance. They include both monochrome and mosaic-glass inlays, and they date from the first half of the eighth century BC.
It has been suggested that the monochrome inlay pieces were cast by the ivory carvers themselves, while the mosaic-glass inlays, since their preparation required considerable skill and training, were probably made by specialist glass-makers. It remains uncertain whether the two types of inlay were made by Phoenician craftsmen from local sources or, alternatively, were imported either in a raw or in a finished state from elsewhere.
Glass vessels make their reappearance soon after the initial production of the ivory inlays. In Mesopotamia this took the form of a revival of the core-formed industry of the Late Bronze Age. Its recommencement has been dated to the second half of the eighth century B. These core-formed vessels were apparently not as highly prized as the cast and cut vessels to be discussed below, since they occur more frequently in private graves than in association with the royal palaces.
The vessels were, however, exported in the seventh century BC to Iran and numerous examples of a local Neo-Elamite industry at Susa are clear imitations of the Mesopotamian types.
Other isolated core-formed vessels have been found at the Urartian site of Karmir Blur, as well as in Syria and Palestine. A significant number of core-formed alabastra have been found on the island of Rhodes. This suggests that either they reached Rhodes from Mesopotamia or they were produced in Rhodes by migrant Mesopotamian craftsmen.
Rhodes, indeed, became the main centre of production for core-formed vessels in the mid-sixth century BC, and it was probably from there that the craft spread through the Mediterranean and Black Sea regions. By far the most interesting type of the Iron Age glass-ware, in terms of technique, decoration and intrinsic value, is the group of cast and cut vessels.
They differ considerably from glass vessels of the Bronze Age in their appearance and method of manufacture. The vessels were cast in moulds, probably by the lost-wax technique and then finished by grinding, cutting, drilling and polishing-techniques borrowed from the makers of stone vessels.
Luxury metal and stone vessels frequently served as prototypes not only for shape, but also for the horizontal grooves and ridges that characterize some of the vessels.
In contrast to the majority of earlier glass, these were monochrome vessels, usually made in translucent, almost colourless or light greenish glass. The glass-makers were evidently imitating rock-crystal or transparent semi-precious stones and not the opaque lapis lazuli or turquoise that had attracted craftsmen in the second millennium BC. This preference for translucent glass shows, most importantly, a new awareness of the special qualities of the substance with which they worked.
The largest and most important group of cast vessels comes from the Assyrian palaces at Nimrud. The Sargon Vase provides a terminus ante quem of BC for the beginning of these cast and cut luxury glass vessels, although most of the Nimrud fragments were found in the debris of the BC destruction.
In addition to the plain bowls, some pieces have superb wheel-cut decoration and two fragments of another bowl reveal inlaid and painted decoration.
These stand as examples of the consummate skill of the glass-makers of the time, combining the use of lost-wax casting, cutting, painting and mosaic-glass inlaying.
At a somewhat lower level of craftsmanship, there are a small number of glass cosmetic palettes from Palestine, notably from the site of Megiddo.
They closely resemble the stone palettes that are relatively common in the same area; Megiddo itself has yielded thirty-five such examples. There is no evidence that glass was made in Palestine in the eighth to seventh centuries BC. The glass used for making the palettes is similar to that used for the cast and cut vessels described above.
These, too, are believed to be the products of Phoenician craftsmen, as indeed the stone and occasional faience palettes are thought to be.
Although it has long been recognised that these vessels form a coherent group with a fairly well-defined chronology, the place of origin has been the subject of much controversy. The industry should be attributed to Phoenicia or, in the case of the Nimrud pieces, to Phoenician craftsmen working for the royal palaces in Assyria.
So, it would appear that the Phoenicians played a major role in the production of glass in the Iron Age. The eclectic nature of Phoenician art is reflected in the ability of its glass-makers to supply a luxury product to a variety of different markets. The Classical Period Between the sixth and first centuries BC the largest share of glass production was devoted to the making of core-formed vessels.
These were almost exclusively small bottles intended for holding scented oils, unguents, perfumes and cosmetics. The bottles and their contents became part of everyday life; they were used in the home, were offered as votives at sanctuaries to the gods and were used at funerals to anoint the dead. Their shapes consciously imitate those of Greek pottery but they stand out from them because of their brilliant colouring and vivid patterns.
Three successive periods of production have been identified, each delineated by a new repertory of forms, decorative motifs, handle forms and colour combinations. The bottles circulated widely in the lands bordering the Mediterranean, but no factory site has yet been discovered and thus it remains uncertain where precisely they were made.
Various locations have been suggested-Rhodes, Cyprus, southern Italy and the coastal cities of Phoenicia. It is likely, in fact, that there were a number of different centres, each producing its own variants.
In the fifth century BC a new industry, using the lost-wax technique, started production under the auspices of the Achaemenid Persians. It specialised in finely made luxury tableware whose shapes and cut decoration were modelled on those of metal vessels.
Most of this tableware was made from a colourless glass in direct imitation of rock crystal. The largest known assemblage of Persian glass-ware was recovered from the treasury at Persepolis, the royal palace destroyed in BC during Alexander the Great's conquest of the Achaemenid Empire.
Other examples have been found in disparate and far-flung locations. It has, therefore, been difficult to determine whether the industry was based in the Persian heartland, or in one of the western satrapies, or even in a Greek city on the periphery of the Empire. However, the close correlation between the glass vessels and Persian silverware combined with the evidence from Persepolis, shows clearly that the industry, wherever it was located, depended heavily on the patronage of the Achaemenid court.
The Hellenistic Period In the Hellenistic world there were two main centres of glass-making, the Syrian coast and Alexandria, the capital of the Ptolemaic kingdom of Egypt.
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