| an glass refers to handblown or individually | | | | Mediterranean. Window glass was quite commonly |
| created glass items, as opposed to items such as | | | | used in the area by 100 BC, such as thick, |
| standardized glass windows and other | | | | translucent samples found in Karanis, Egypt. |
| mass-produced products. Until a few hundred | | | | The expansion of the Roman empire and |
| years ago, this description fit virtually all glass | | | | widespread trade brought glass-making technology |
| products. | | | | to Europe, the British Isles and China. After the fall |
| Common glass contains about 70% amorphous | | | | of the Roman empire, their advanced |
| silicon dioxide, the same chemical composition as | | | | glass-making technology fell out of use, and glass |
| quartz and sand. Commercial glass can be made | | | | production declined until the seventh century, |
| of pure silica, but usually sodium carbonate (soda) | | | | when Europeans once more began to revive the |
| and calcium oxide (lime) are added. Various other | | | | use of glass for a variety of purposes. The |
| additives are also used, such as lead to give glass | | | | beautiful stained-glass windows on European |
| more "sparkle." Forms of glass that do not include | | | | cathedrals did not begin to be made until the 12th |
| silica as a major component are sometimes used | | | | century. |
| for fiber optic cables and other specialized | | | | Venice developed into a glass-making center in |
| technical applications. | | | | the 14th century, and the city became the hub of |
| Metals and metal oxides have long been used to | | | | a lucrative export trade in dinner ware, mirrors, |
| give color to glass. Brilliantly colored cobalt blue | | | | beads, and other luxury items. Venetian glass was |
| glassware is a collectors' item. Glass can also be | | | | of unusually high quality because the local quartz |
| colored with minerals including iron oxide (brown), | | | | stones used in its production were almost pure |
| chromium (green) , manganese (purple), selenium | | | | silica. These stones were ground into a fine clear |
| (pink or red), or combinations thereof. The | | | | sand which was blended with another locally |
| method of heating and cooling the glass during its | | | | occurring product called "Levant soda ash", for |
| processing can significantly affect the colors | | | | which the Venetians held the sole monopoly. Even |
| produced by these compounds, in a process | | | | today, multicolored handmade glass beads are |
| whose chemistry is complex and poorly | | | | called "Venetian glass." |
| understood. | | | | The Crown glass process of glass pane |
| Lightning strikes which fuse sand can leave glass | | | | production was used up to the mid-1800s. A |
| trails resembling tree roots along the path of the | | | | glassblower would spin around 9 pounds of molten |
| electrical discharge. Another naturally occurring | | | | glass at the end of a rod until it flattened into a |
| glass, obsidian, has been used by humans since | | | | disk approximately 5 feet in diameter, which was |
| the stone age. The Phoenicians used glass as | | | | then cut into panes. Before float glass was |
| pottery glaze in 3000 BC, and glass beads, seals | | | | invented, sheet glass was never completely |
| and architectural decorations found in | | | | uniform, and in historical buildings, some of these |
| Mesopotamia date back to 2500BC. The first | | | | panes of slightly wavy glass can still be seen. In |
| glass was created by melting sand, producing a | | | | antique shops, it is still possible to find old |
| greenish product due to the naturally-occurring | | | | apothecary bottles, each a slightly different size, |
| iron oxide in the sand. Even today, commercial | | | | produced by glass blowers. |
| glass has a slight green or blue tint, due to the | | | | Around 1688, glass casting was introduced, leading |
| presence of these same impurities. Egyptians | | | | glass to become a common, widely used material. |
| made glass beads and glass bottles dating to 1500 | | | | The invention of the glass pressing machine in |
| BC. By 500 BC, glass-making technology had | | | | 1827 allowed the mass production of inexpensive |
| spread to Greece, and by 100 BC there were | | | | glass articles. Handmade, irregular items are now |
| many glass-making centers around the | | | | strictly the purview of artists. |