Colorful Glass World
2008-08-14

                                                                                                 Colorful Glass World

When glass excavated by human, a vary shape of glass appeared in the front of people’s eyes. Also, varies colors of glasses attract us, how do they come into being? Ordinary glass appears colorless to the naked eye when it is thin, although iron oxide impurities produce a green tint which can be viewed in thick pieces or with the aid of scientific instruments. Further metals and metal oxides can be added to glass during its manufacture to change its color.

A) Processes Early glass derived its color from impurities that were present when the glass was formed. For example, 'black bottle glass' was a dark brown or green glass, first produced in 17th Century England. This glass was dark due to the effects of the iron impurities in the sand used to make the glass and the sulfur from the smoke of the burning coal used to melt the glass. In addition to natural impurities, glass is colored by purposely introducing minerals or purified metal salts (pigments). Examples of popular colored glasses include ruby glass (invented in 1679, using gold chloride) and uranium glass (invented in the 1830s, glass that glows in the dark, made using uranium oxide). Sometimes it is necessary to remove unwanted color caused by impurities to make clear glass or to prepare it for coloring. Decolorizes are used to precipitate out iron and sulfur compounds. Manganese dioxide and cerium oxide are common decolorizes.

B) Special Effects Many special effects can be applied to glass to affect its color and overall appearance. Iridescent glass, sometimes called iris glass, is made by adding metallic compounds to the glass or by spraying the surface with stannous chloride or lead chloride and reheating it in a reducing atmosphere. Ancient glasses appear iridescent from the reflection of light off of many layers of weathering. Diachronic glass is an iridescent effect in which the glass appears to be different colors, depending on the angle from which it is viewed. This effect is caused by applying very thin layers of colloidal metals (e.g., gold or silver) to the glass. The thin layers are usually coated with clear glass to protect them from wear or oxidation. Some examples of glass pigments are listed below: 1. Iron (II) oxide results in bluish-green glass, frequently used for beer bottles. Together with chromium it gives a richer green color, used for wine bottles. 2. Sculpture, together with carbon and iron salts, is used to form iron polysulphides and produce amber glass ranging from yellowish to almost black. In borosilicate glasses rich in boron, sculpture imparts a blue color. With calcium it yields a deep yellow color. 3. Manganese can be added in small amounts to remove the green tint given by iron, or in higher concentrations to give glass an amethyst color. Manganese is one of the oldest glass additives, and purple manganese glass was used since early Egyptian history. 4. Manganese dioxide, which is black, is used to remove the green color from the glass; in a very slow process this is converted to sodium permanganate, a dark purple compound. In New England some houses built more than 300 years ago have window glass which is lightly tinted violet because of this chemical change; and such glass panes are prized as antiques. 5. Selenium, like manganese, can be used in small concentrations to decolorize glass, or in higher concentrations to impart a reddish color, caused by selenium atoms dispersed in glass. It is a very important agent to make pink and red glass. When used together with cadmium sulfide, it yields a brilliant red color known as "Selenium Ruby". 6. Small concentrations of cobalt (0.025 to 0.1%) yield blue glass. The best results are achieved when using glass containing potash. Very small amounts can be used for decolorizing. 7. Tin oxide with antimony and arsenic oxides produce an opaque white glass, first used in Venice to produce imitation porcelain. 8. 2 to 3% of copper oxide produces a turquoise color. 9. Pure metallic copper produces a very dark red, opaque glass, which is sometimes used as a substitute for gold in the production of ruby-colored glass. 10. Nickel, depending on the concentration, produces blue, or violet, or even black glass. Lead crystal with added nickel acquires purplish color. Nickel together with small amount of cobalt was used for decolorizing of lead glass. 11. Chromium is a very powerful colorizing agent, yielding dark green or in higher concentrations even black color. Together with tin oxide and arsenic it yields emerald green glass. Chromium aventurine, in which aventurescence was achieved by growth of large parallel chromium (III) oxide plates, was also made from glass with added chromium. 12. Cadmium together with sculpture results in deep yellow color, often used in glazes. However, cadmium is toxic. 13. Adding titanium produces yellowish-brown glass. Titanium is rarely used on its own, is more often employed to intensify and brighten other colorizing additives. 14. Metallic gold, in very small concentrations (around 0.001%), produces a rich ruby-colored glass ("Ruby Gold"), while lower concentrations produces a less intense red, often marketed as "cranberry". The color is caused by the size and dispersion of gold particles. Ruby gold glass is usually made of lead glass with added tin. 15. Uranium (0.1 to 2%) can be added to give glass a fluorescent yellow or green color. Uranium glass is typically not radioactive enough to be dangerous, but if ground into a powder, such as by polishing with sandpaper, and inhaled, it can be carcinogenic. When used with lead glass with very high proportion of lead, produces a deep red color. 16. Silver compounds (notably silver nitrate) can produce a range of colors from orange-red to yellow. The way the glass is heated and cooled can significantly affect the colors produced by these compounds. The chemistry involved is complex and not well understood. 

Image it: we live in a colorful glass world, which is a wonderful thing, Colored glasses are not only giving us the enjoyment of the visual, but also bring us comfortable living environment. Love them: colorful glass.