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Roman glass objects have been recovered across the Roman Empire in domestic, industrial and funerary contexts. Glass was used primarily for the production of vessels, although mosaic tiles and window glass were also produced. Roman glass production developed from Hellenistic technical traditions, initially concentrating on the production of intensely coloured cast glass vessels. However, during the first century AD the industry underwent rapid technical growth that saw the introduction of glass blowing and the dominance of colourless or ‘aqua’ glasses. Production of raw glass was undertaken in geographically separate locations to the working of glass into finished vessels,[1][2] and by the end of the first century AD large scale manufacturing resulted in the establishment of glass as a commonly available
Glass is basically sand; like the stuff you find on the beach, officially know as silicone dioxide. To the sand they add a soda , officially sodium carbonate not too unrelated to that you wash or cook with. That lowers it's melting point. And they also add lime, as in ancient shells and coral, as a stabilizer. Other ingredients can be added to get special effects. Lead for brilliance, boron for heat resistance, barium to increase refractibility, metal oxides for colour (that's why they call it Cobalt Blue) or manganese for decolourization. Glass is a remarkable substance, made from the simplest raw materials Glassware can be colored or colourless, monochrome or polychrome, transparent, translucent or opaque. Itis lightweight, impermeable to liquids, readily cleaned and reused, durable yet fragile, and often very beautiful. Glass can be decorated in different ways and its optical properties are exceptional. They are used for as in cups, bowls, dishes, glass windows on your house and car. Glass is actually a major achievement in the history of technological developments.
Glass is a hard material normally fragile and transparent common in our daily life. It is composed mainly of sand (silicates, SiO2) and an alkali. These materials at high temperature (i.e. molten viscous state) fuse together; then they are cooled rapidly forming a rigid structure. Depending on the final use and application the composition of the glass other materials are added according to its use to get the final product • These are the common ingredients to obtain glass:1. Sand (SiO2 silica)In its pure form it exists as a polymer, (SiO2)n. 2. Soda ash (sodium carbonate Na2CO3) 3. Limestone (calcium carbonate or CaCo3) or dolomite (MgCO3)Also known as lime, calcium carbonate is found naturally as limestone, marble, or chalk.The soda makes the glass water-soluble, soft and not very durable. Therefore lime is added increasing the hardness and chemical durability and providing insolubility of the materials. Other materials and oxides can be added to increase properties (tinting, durability, etc.), produce different effects, colors, etc. The main types of glass are described below:Commercial glass or Soda-lime glass:This is the most common commercial glass and less expensive. The composition of soda-lime glass is normally 60-75% silica, 12-18% soda, and 5-12% lime. A low percentage of other materials can be added for specific properties such as coloring. - It has light transmission appropriate to be use in flat glass in windows; - It has a smooth and nonporous surface that allows glass bottles and packaging glass to be easily cleaned; - Soda-lime glass containers are resistant to chemical attack from solutions so they will not contaminate the contents inside or affect the taste. Whereas pure glass does not absorb UV light, soda-lime glass does not allow light at a wavelength of lower than 400 nm (UV light) to pass. The disadvantages of soda-lime glass is that is not resistant to high temperatures and sudden thermal changes. For example, everybody has experienced a glass breaking down when pouring liquid at high temperature, for example to make tea. Some of the use of soda-lime glass is primarily used for bottles, jars, everyday drinking glasses, and window glass. • Borosilicate glass: Borosilicate glass is mainly composed of silica (70-80%), boric oxide B2O3 (7-13%) and smaller amounts of the alkalis (sodium and potassium oxides) such as 4-8% of Na2O and K2O, and 2-7% aluminum oxide (Al2O3). Boron gives greater resistance to thermal changes and chemical corrosion making It is suitable for industrial chemical process plants, • or for laboratories with bulbs for high-powered lamps, etc. Borosilicate glass is also used in the home for cooking plates and other heat-resistant products. It is used for domestic kitchens and chemistry laboratories, becauseit has resistance to thermal shock and allows for greater accuracy in laboratory experiments when heating and cooling.
Glass, an amorphous substance made primarily of silica fused at high temperatures with borates or phosphates. Glass is also found in nature, as the volcanic material obsidian and as the enigmatic objects known as tektites (see Tektite). It is neither a solid nor a liquid but exists in a vitreous, or glassy, state in which molecular units have disordered arrangement but sufficient cohesion to produce mechanical rigidity. Glass is cooled to a rigid state without the occurrence of crystallization; heat can reconvert glass to a liquid form. Usually transparent, glass can also be translucent or opaque. Color varies with the ingredients of the batch. Molten glass is plastic and can be shaped by means of several techniques. When cold, glass can be carved. At low temperatures glass is brittle and breaks with a shell-like fracture on the broken face. Such natural materials as obsidian and tektites (from meteors) have compositions and properties similar to those of synthetic glass. Glass was first made before 2000 BC and has since served humans in many ways. It has been used to make useful vessels as well as decorative and ornamental objects, including jewelry. Glass also has architectural and industrial applications. The basic ingredient of glass compositions is silica, derived from sand, flint, or quartz. • Plastic is the general common term for a wide range of synthetic or semisyntheticorganic solid materials suitable for the manufacture of industrial products. Plastics are typically polymers of high molecular weight, and may contain other substances to improve performance and/or reduce costs. • The word derives from the Greekπλαστικός (plastikos), "fit for molding", from πλαστός(plastos) "molded" [1][2]. It refers to their malleability, or plasticity during manufacture, that allows them to be cast, pressed, or extruded into an enormous variety of shapes—such as films, fibers, plates, tubes, bottles, boxes, and much more. • The common word "plastic" should not be confused with the technical adjective "plastic", which is applied to any material which undergoes a permanent change of shape (a "plastic deformation") when strained beyond a certain point. Aluminum, for instance, is "plastic" in this sense, but not "a plastic" in the common sense; while some plastics, in their finished forms, will break before deforming — and therefore are not "plastic" in the technical sense.
Plastic is the general common term for a wide range of synthetic or semisyntheticorganic solid materials suitable for the manufacture of industrial products. Plastics are typically polymers ofhigh molecular weight, and may contain other substances to improve performance and/or reduce costs. • The word derives from the Greek πλαστικός(plastikos), "fit for molding", from πλαστός(plastos) "molded". It refers to their malleability, or plasticity during manufacture, that allows them to be cast, pressed, or extrudedinto an enormous variety of shapes—such as, films, fibers plates, tubes, bottles, boxes, and much more. • The common word "plastic" should not be confused with the technical adjective "plastic", which is applied to any material which undergoes a permanent change of shape (a "plastic deformation") when strained beyond a certain point. Aluminum, for instance, is "plastic" in this sense, but not "a plastic" in the common sense; while some plastics, in their finished forms, will break before deforming — and thereforeare not "plastic" in the technical sense.
Plastics are "one of the greatest innovations of the millennium“ and have certainly proved their reputation to be true; it has been the most used material in the United States since 1976. Plastic is lightweight, does not rust or rot, helps lower transportation costs and conserves natural resources is the reason for why plastic has gained this much popularity. Plastics are everywhere and have innumerable uses! Plastics are durable, lightweight, and reusable. Also, they are used in packaging many goods. Did you know that researches are trying to make a television (made of plastic) that will roll up in your living room? Since plastic is an insulator, plastic is used to cover almost all wires and electric cords. Did you know that if the Titanic was made of plastic, it might still be cruising around the world? Plastics are colossal in many people's current lifestyle, and will be in their future lifestyle.Although plastic has many positive influences in everyday lives, there have been times when plastics have posed some health and environmental hazards. Most plastics do not pose any hazards, but some substances that are used inmanufacturing plastics, have been proved to cause cancer. Also, a raw material used in the production of nyloncauses cancer. Even though recycling continues to reuse plastics, most plastics do not rot and can not be reused. Unfortunately, this will soon become an environmental problem: Where will the plastic be disposed? But, many researchers hope to find a solution to this dilemma in the future. When every plastic can be broken down, plastic will truly become the most useful product! • http://library.thinkquest.org/C003844/a_effects.htm
Plastics, materials made up of large, organic (carbon-containing) molecules that can be formed into a variety of products. The molecules that compose plastics are long carbon chains that give plastics many of their useful properties. In general, materials that are made up of long, chainlike molecules are called polymers. The word plastic is derived from the words plasticus (Latin for “capable of molding”) and plastikos (Greek “to mold,” or “fit for molding”). Plastics can be made hard as stone, strong as steel, transparent as glass, light as wood, and elastic as rubber. Plastics are also lightweight, waterproof, chemical resistant, and produced in almost any color. More than 50 families of plastics have been produced, and new types are currently under development. Like metals, plastics come in a variety of grades. For instance, nylons are plastics that are separated by different properties, costs, and the manufacturing processes used to produce them. Also like metals, some plastics can be alloyed, or blended, to combine the advantages possessed by several different plastics. For example, some types of impact-resistant (shatterproof) plastics and heat-resistant plastics are made by blending different plastics together. Plastics are moldable, synthetic (chemically-fabricated) materials derived mostly from fossil fuels, such as oil, coal, or natural gas. The raw forms of other materials, such as glass, metals, and clay, are also moldable. The key difference between these materials and plastics is that plastics consist of long molecules that give plastics many of their unique properties, while glass, metals, and clay consist of short molecules. Plastics are indispensable to our modern way of life. Many people sleep on pillows and mattresses filled with a type of plastic—either cellular polyurethane or polyester. At night, people sleep under blankets and bedspreads made of acrylic plastics, and in the morning, they step out of bed onto polyester and nylon carpets. The cars we drive, the computers we use, the utensils we cook with, the recreational equipment we play with, and the houses and buildings we live and work in all include important plastic components. The average car contains almost 136 kg (almost 300 lb) of plastics—nearly 12 percent of the vehicle’s overall weight. Telephones, textiles, compact discs, paints, plumbing fixtures, boats, and furniture are other domestic products made of plastics. In 1979 the volume of plastics produced in the United States surpassed the volume of domestically produced steel.
Plastics are made from oil. Oil is a carbon-rich raw material, and plastics are large carbon-containing compounds. They're large molecules called polymers, which are composed of repeating units of shorter carbon-containing compounds called monomers. Chemists combine various types of monomers in many different arrangements to make an almost infinite variety of plastics with different chemical properties. Most plastic is chemically inert and will not react chemically with other substances -- you can store alcohol, soap, water, acid or gasoline in a plastic container without dissolving the container itself. Plastic can be molded into an almost infinite variety of shapes, so you can find it in toys, cups, bottles, utensils, wiring, cars, even in bubble gum. Plastics have revolutionized the world. Because plastic doesn't react chemically with most other substances, it doesn't decay. Therefore, plastic disposal poses a difficult and significant environmental problem. Plastic hangs around in the environment for centuries, so recycling is the best method of disposal. However, new technologies are being developed to make plastic from biological substances like corn oil. These types of plastics would be biodegradable and better for the environment. In this article, we'll examine the chemistry of plastic, how it's made, how it's used, and how it's disposed of and recycled. We'll also look at some new biologically based plastics and their role in the future of plastic. http://science.howstuffworks.com/plastic.htm
websites http://inventors.about.com/od/gstartinventions/a/glass.htm http://EzineArticles.com/?expert=Sylvia_Kittens http://en.wikipedia.org/wiki/Roman_glass http://www.memories-in-glass.com/glass-what-is-it1.htm http://encarta.msn.com/encyclopedia_761554489/Glass.html http://en.wikipedia.org/wiki/Plastic http://www.lenntech.com/glass.htm • http://library.thinkquest.org/C003844/a_effects.htm
