By the late 16th century glass-making had become an important industry in northern Europe. French, German and British glass makers had discovered the secret the of the Venetians and had reduced the cost markedly.
The crown glass process was perfected by French glass makers in 1320 and was a trade secret until it was made in 1678 London. A glassblower spun about 9 pounds (4 kg) of molten glass at the end of a rod until it flattened into a disk approximately 5 feet (1.5 m) in diameter. The disk would then be cut into panes that were joined with lead strips to form windows. By the early 1800's, crown glass had become commonly for windows in Western Europe and in the USA.
In 1674, George Ravenscroft added lead oxide to glass and patented a glass, with a high refractive index and a low melting temperature, that could be easily cut and engraved.
In France, in 1688, Louis Lucas de Nehou and Abraham Thevart poured molten glass onto an iron table and rolled it flat to make very large glass plates. When it had cooled, they ground the glass plate on large round tables using rotating cast iron discs and increasingly fine abrasive sands. They then made mirrors by coating one side with a reflective metal, like tin, having a low melting point.
Ravenscroft adopted the French technique in 1773 and, in 1800, began using a steam engine for the labourious work of grinding and polishing the cast glass.
In 1798, P.L.Guinand, a Swiss bell founder, used a fire clay stirrer to more uniformly distribute the heavy lead oxide in glass and reduce the size of air bubbles. The denser glasses increased the range of refractivity and Joseph von Fraunhofer, the spectroscopist at the Munich optical institute, was able to produce large, high quality glass lenses.
Between 1750 and 1850 most bottles were black or very dark green because of iron and other impurities in the glass. Drinking glasses were made with more expensive clear glass.
The traditional colour for blue glass was obtained with cobalt but more colours were obtained by adding carefully controlled amounts of purified chromium, manganese, copper, sulphur, uranium and nickel. These made a large range of colours for stained glass windows.
By 1825, molten glass, blown into the shape of a cylinder, was cooled, sliced down one side, reheated, opened up and flattened to form a large sheet of thin window glass. In 1851, Joseph Paxton built the Crystal Palace in London to house the Great Exhibition. The huge, revolutionary building inspired the use of glass for architectural purposes.
By 1886, Ernst Abbe and Otto Schott had joined Karl Zeiss at the Jena glassworks and by the end of the century they had listed about 80 different optical glasses using more than 29 elements not previously used in glass-making.
In 1887, the British company, Ashley, developed a process where two machines and two men could make 200 glass bottles per hour, making them many times cheaper than traditional bottles. Previously, 5 men had produced only 150 bottles per hour.
In 1903, the American, Michael J. Owens, invented a fully automatic bottle-blowing machine capable of producing 2,500 bottles an hour. This continually sucked a blob of molten glass into a metal mould where it was blown into shape and cut off automatically.
In 1905, Émile Fourcault, a Belgian engineer, invented a process of vertically drawing a continuous sheet of glass from a tank of molten glass. At the bottom of the draw, where the molten glass was cooled to near the forming temperature, a ribbon of glass was drawn vertically up from a narrow slit in a ceramic forming die. The glass changed from a hot syrupy mass at the die into a continuous, solid flat glass ribbon and was cooled and shaped by rollers. Finally the flat plate glass was cut into the desired sizes. In 1918, another Belgian engineer, Emil Bicheroux, poured molten glass from a pot through two rollers. Both processed produced plate glass with a more uniform thickness making polishing and grinding easier.
Glass was strengthened by laminating a celluloid material between two glass sheets in a process invented by French scientist Edouard Benedictus in 1910.
The float glass process was perfected in Britain by Pilkington Brothers Ltd. in 1959. Molten glass was poured across the surface of a bath of molten tin where it flattened before it was drawn horizontally in a continuous ribbon into an annealing furnace.
Float glass combined the optical qualities of plate glass with the brilliant finish of sheet glass and today, most flat glass is made by this process.
Borosilicate glass (trademark PYREX®), which can withstand extreme changes of temperature (unlike normal glass which shatters) is made by adding boron oxide to the molten mixture.
Toughened glass used in car windshields is made by cooling molten glass very quickly to make it much harder. Bulletproof glass is made by bonding many layers of glass and plastic together.
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Middle Era
Non-FictionJesus and Muhammad adopted the Hebrew's belief in one God and Christianity and Islam spread throughout the world. The Chinese were using gunpowder in the 9th century and, by the 13th , cannon dominated the battlefields. Paper money appeared in China...
