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英国essay论文精选范文：“天然玻璃”，这篇论文讨论了天然玻璃。天然玻璃就是在自然条件下形成的玻璃。火山喷发、陨石撞击或者雷击等自然现象的发生，会让一些岩石发生变化，最终形成天然玻璃。作为一种比较稀有的矿石，天然玻璃大多数会被制造成艺术品或者珠宝。

Natural glass has existed ever since the universe was formed in the crucible of the big bang. Naturally occurring glass is formed when certain types of rocks melt as a result of high-temperature phenomena such as volcanic eruptions, lightning strikes or the impact of meteorites, and then cool and solidify rapidly. Glass that is made as a result of the collision of a meteorite with the Earth's surface is called meteoritic glass or tektite. Glass that is made as a result of a lightning strike is called fulgurites. Fulgurites come in an immense variety of forms and can be labeled nature's own works of art. Glass, however, would not be left as an untapped natural resource for very long in human history. Obsidian is one of the more commonly Referenced forms of lightning-formed glass and was used by ancient Mayan and Aztec civilizations in jewelry, and more importantly, was used to grant an edge to these civilizations militaries. Even so, glass was discovered and referenced long before that.

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The discovery of glass is among the most momentous occurrences throughout human development, glass has many uncommon characteristics: its translucence, transparency and its innumerable functional uses. It is extremely easy to overlook the aesthetic in light of the plethora of personal, ceremonial, and other capabilities. Glass has been around for over five-thousand years, and its complex and ancient history reveals a multitude of aesthetic possibilities. Some techniques have totally vanished, whereas others are rediscovered later in the course of human history. The ancient-Roman historian Pliny, CE 23-79, claimed that Phoenician merchants transporting stone actually discovered glass in Syria around 5000 BCE. Pliny tells how the merchants, after arriving to solid ground, rested cooking pots on blocks of nitrate placed by their fire. With the extreme heat of the fire, the blocks ultimately melted and mixed with the sand of the beach to create an opaque liquid (MacFarlane and Martin, 10). Glass created during this time had three major purposes: to glaze pottery, create jewelry, and to store liquids as containers. Around 500 BCE, these techniques spread to Asia and became known to the Chinese. Until then, the major technique of creating glass containers and jewelry was to use a system known as 'core-forming' (MacFarlane and Martin, 11).

Around 1650 BCE, with the introduction of the core-forming technique the production of small glass containers began. Core forming was one of the most widespread methods before the discovery of blown glass. This technique involved taking a core of organic materials, clay, sand, and manure in the shape of the vessel's interior. This amalgamation is then attached to a rod of metal and inserted into a crucible as it is turned on the rod. Heat is then applied to the surface and the object is rolled over an even area, usually slate, to compress it. At this point, colored threads are applied and combed with a special tool. Bases, pouring lips, and handles are also added to the vessel in this step. The most important step in the process is separating from the rod and scraping the core out. The glass could then be used for various types of storage. Depending on the recipient and purpose of the newly formed container, the crafter could scrape and 'paint' various patterns and decorations on the vessel before it completely cooled off (Macfarlane and Martin, 12).

Romans have played one of the most significant roles in the development of glass technology. Their techniques and technology had been virtually unrivalled until the 19th century. The possibilities of innovation coincided with the peak of Roman civilization, which, at the time, placed glass at the center of interior decorations purposes. With their development of glass blowing, many vessels and decorations could be produced quickly, effectively, and in large quantities. Glass, being such a fine and versatile substance, became a symbol of wealth and a highly prized possession. Because of its popularity and success, glass even began to undermine the significance of ceramics, which was their main competitor until then (Stern, 34). This time of history is widely believed to have been the time in which glass was harnessed and utilized the most out of any other era. Glass was principally used for various forms of storage or holding: dishes, bottles, jugs, cups, plates, spoons, lamps, and inkwells. To add more to the list, glass was also involved in creating pavements and drainpipes (Stern, 37). All in all, glass was a major technological breakthrough, however it was also a significant cultural breakthrough - imagine how different the favorite Roman drink, wine, would appear in a grimy clay mug rather than a pristine, fine glass. In all other civilizations outside of western Eurasia, glass was still chiefly used as an opaque material intended to mimic precious stones (Stern, 48).

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How is the transparent and translucent look achieved by the Romans? The incredibly significant advance that allowed them to showcase the colors of the luxurious wines was the technology of glass blowing. A breakthrough around 27 BCE and 14 CE involved using a completely different approach to designing glass vessels. The advent of glassblowing proved to be revolutionary to glass-making. Glassblowing allowed items to be created in a much quicker fashion as it allowed for standardized production using molds. In addition, this advent made it possible to cast off the dependence on prior shapes, as glassblowing made it possible to form any original shape and allowed for enlargement (Cummings, 57). Glassblowing quickly became the de facto method of forming items throughout the Roman Empire. This created a vast influx of glass items as large parts of society acquired glass and began using it in day-to-day life (MacFarlane and Martin, 17). Roman crafters would use a long, thin, and hollow metal tube instead of any clay cores. A gob of molten glass is applied to the far end of the pipe, and the crafter blows into the near end whilst spinning the pipe rapidly. The force of the air would cause the molten glass to bubble out, and the gravitational pull from the spinning pipe would keep the glass symmetrical and round as it expanded. More and more layers of liquid glass are added, and the final shaping touches are applied with tools to create a base and lip for the vessel. After it gets cooler, the piece is carefully broken off the pipe and set down to finish hardening (Stern, 20-34).

A further advancement by the Romans was a technique called mold-forming or kiln-forming. This is achieved by placing the pipe inside of a pre-made mold, and blowing the molten glass gob inside of it until it fills it up and presses against the insides of the mold. After the mold has been filled up by the glass, the glass blower's assistant(s) remove pieces of the mold from around the pipe. The pipe was held vertically so that gravity would not cause the molten glass to become asymmetrical. Then it is removed and further shaped (Stern, 45). Kiln-forming allowed for more intricate and advanced vessels. Even so, not everything was perfect with these vessels. When cups, vases, and other containers were made, the lips were usually lightly grounded had a slightly sandpapery texture, rather than the smooth, sleek texture most people today enjoy. The reason the Romans had these issues was because when the glass was gently broken off of the pipe, the edges of the lip would be sharp (Cummings, 47). The edges would be ground up until the sharp edges were gone, leaving a symmetrical but slightly different-textured finish (Stern, 45). Folded rims were the solution to this issue. Roman glass blowers would, instead of waiting for the rims to cool for grinding, reheat the neck of the vessel and manipulate it in such a way that the rim collapsed inward to form a lip folded outward, upward, and inward. All of this was skillfully done without even touching the glass - merely using heat and gravity; the glass blower could achieve this effect (Stern, 45).

Because of the ease of production brought on by glassblowing, many glass artisans feared loss of prestige and societal standing due to the possibility of mass production. In response, they developed new and inventive processes fusing formative and decorative shapes into some of the most prized pieces of luxury glassware that have ever existed (Cummings, 174). Stained glass, sheet glass, and mosaic glass were all the products of artisans experimenting with developing new techniques.

The invention of sheet glass by the Romans in the first century CE was the earmark of using glass for windows in a building. Sheet glass is creating by blowing glass on a pipe, like normal, but the glass bubble would be raised up and spun as if spinning a lasso and the gravitational pull would flatten the glass out in a sheet a few meters in diameter, depending on the purpose it was being made for. The sheets were trimmed into rectangles and fused together with lead strips, effectively forming a window grid. This glass wasn't perfectly flat, of course, nor was it perfectly transparent. The windows made from these sheets of glass were cloudy, but they still served the purpose of letting light in and keeping the elements out. These windows, at first, were only installed in the homes of the wealthy, upscale churches, and government buildings (Cummings, 175). Even then, more efficient methods of production were discovered for producing sheet glass and most people eventually had glass windows installed in their homes and businesses. Glassmaking artisans then went on to produce even more expensive and unique works of art.

Stained, or colored art glass, is one of the most commonly referenced type of artistic glass. One of the oldest known examples of multiple pieces of colored glass used in a window were unearthed at St. Paul's Monastery in Jarrow, England, founded in 686 CE. The process to create a piece of stained glass is quite complex. The Artist will create a template and rough sketch to show the overall layout, these templates were traditionally made using large cuts of stone or wood as paper was a luxury not to be wasted. After the template was finalized the artist would hand select each piece of glass to correspond to specific objects or areas. Smaller details including faces, hair, hands, writing were painted directly onto the glass using special paints mixed from smashed bits of glass, finely ground lead and copper fillings, and other mediums such as vinegar, wine, or urine. Only after the glass is cut and painted are the pieces assembled by inserting neighboring pieces into lead cames; joints are then soldered together and weatherproofing is applied using soft oily cement (GlassFacts.info). John La Farge (March 1835 - November 1910) invented opalescent glass which is extensively used in Tiffany style windows and lamps (Conservation Research Laboratory).

Venetian and Murano glass are forever intertwined as the glass artisans in Venice were forced out of the Venetian Republic due to fear the foundries in the city would cause fire and destruction to the city; the glassmakers moved to the nearby city of Murano. These artisans were of such high regard they were allowed to wear swords and were above persecution by local authorities. Murano glassmakers had a monopoly on high quality glass for centuries, during which they developed and refined a multitude of glassmaking technologies. Today the artisans at Murano still employ these centuries' old techniques to produce some of the finest contemporary art glass, chandeliers, glass jewelry and wine glasses (MacFarlane and Martine, 51).

Because glass has always served a very functional use throughout history, it had not always been regarded as fine art. Skilled artisans in the craft never truly remained famous like an artist such as Michelangelo or Monet did even though glassmakers have created some of the most beautiful artistic pieces in history. One historical piece, known as the Portland Vase, has served as inspiration to many glass makers from the beginning of the 18th century onwards. The vase is dated 5-25 CE, and has been held in the British Museum in London ever since 1945. The Portland Vase is a dark violet and blue hue and is adorned with intricate white figures. There are several interpretations of the scenes portrayed on this piece (Stern, 27). Known as a cameo-vessel, the vase was created using the dip-overlay method. An elongated bubble of glass is dipped into a crucible of white glass before the two were blown together, and after they cooled the white layer.

A more modern example of famous glass artwork is not merely one vessel, but instead a whole production line of glass artwork. Louis Comfort Tiffany (February 1848 - January 1933) was an American designer who is best known for his works in stained glass. His company, Tiffany & Company, produced stained glass windows, lamps, glass mosaics, blown glass, ceramics, jewelry, enamels, and metalwork. He is most famous for harnessing opalescent glass in his artwork. Opalescent glass maintains its mineral 'impurities' and appears milky in color and is iridescent. Instead of painting directly onto glass, as had been done for centuries beforehand, Tiffany used glass that already had the color in it. He is most famous for his commercially produced Tiffany lamps, and their production first began around 1895. Although the lamps are the most famous glass art his company produced, a complete range of interior decorations were created as well. At Tiffany's peak, his factory employed more than 300 artisans, several of which were talented females hired to make intricate floral patterns (GlassFacts.info). The Charles Hosmer Morse Museum of American Art in Winter Park, Florida, currently holds the largest and most varied collection of works created by the Tiffany Company.

How can glass be taken care of and preserved? Aside from the obvious vulnerability glass has to physical breakage, cracking, and shattering, there are many ways even the sturdiest and resilient glass can decay. Factors that can accelerate decay in glass include: the type of glass and the manner in which it was manufactured, the amount of moisture, alkalinity, and salts in the burial environment and physical wear or abrasion prior to burial. A major form of manufacture defect that occurs in glass is known as devitrification.

Devitrification occurs in glass during the firing process and is defined by the fired glass developing a whiting scum and wrinkles instead of smooth and glossy shine. The structure of the molecules making up the glass change their structure into crystalline solids, devitrification is usually undesired but is sometimes used as a valid artistic technique. Devitrification is caused when the glass holds too high of a temperature for too long thereby causing chemical elements to be burnt off, or by the existence of foreign residue like dust on the surface of the glass or inside the kiln prior to firing. Proper firing techniques should be used to prevent devitrification. The most common techniques used to prevent this damage include proper cleaning of the glass and interior kiln surfaces and to allow the rapid cooling once the glass attains the desired temperature. If devitrification has already taken place there are some methods of restoration, one such method is to use a sheet of clear glass to cover the surface of a piece and refiring it. Acid baths, sandblasting, polishing with a rotary brush or pumice stone are additional techniques to rid the piece of unwanted surface (Beveridge, Doménech, Pacual, and Pascual i Miró, 66).

Another type of deterioration in glass is known as iridescence. The glass begins to decay from the outer layers inward, forming thin, onion-like layers that appear opaque in different colors from the original glass because the way in which the light is refracted through the glass has been altered. Some other types of deterioration are known as pitting, surface abrasions, and exfoliation. Pitting is when there are secluded holes or indentations in the glass surface or on broken edges. Poor handling and transport can result in surface abrasions, and spalling occurs when the decayed layers separate, flake off, which causes the original surface of the object to vanish (Conservation Research Laboratory).

Alongside impurities brought about during the manufacturing process, glass art is also susceptible to deterioration brought on by improperstorage and faulty care. Delicate collectible items such as art glass, pottery and figurines require specific measures to be taken in order to keep them in pristine condition. Fortunately that is not hard to do with the correct information. It is best to keep glass artwork out of direct sunlight. Exposure to direct sunlight over an extended period of time can fade or alter the color applied to the glass. To clean dust off of a glass work, be sure to handle the item with latex or vinyl gloves, and use a soft bristled brush (such as a cosmetic brush). Another extremely helpful method is to use a can of compressed air to remove dust and impurities. In order to minimize exposure to dust, use a superior method to store art glass. An enclosed curio cabinet or china cabinet is preferred over using open wooden shelving or other unstable, organic materials that are prone to off-gassing (Conservation Research Laboratory).

The discovery of glass has affected mankind's history and culture immensely. When it was first discovered, it was highly revered -mystical in its transparency and numinous in its versatility. The true art of glass production has lost its cultural significance with mainstream manufacture and factories mass producing everyday items such as newer LCD screens in personal computing electronics, automotive glass, and disposable glass bottles. These items are not made with any sort of personal or cultural touch - they are simply mass produced, consumed, and disposed of. Many do not look twice when encountering a colorful vase or an intricately shaped window, but centuries ago these things would have been highly admired and were symbols of success, wealth, and invention. Fortunately, the ancient traditions of glass making through glassblowing, and to a lesser extent, core-forming, have been preserved and still practiced to this day. Although it is used so much in modern day society and is all around us in every form and shape imaginable, it is preferable to believe that we have not become desensitized to its alluring and enthralling characteristics.

References:

1.Beveridge, Philippa, Ignasi Domenech, Eva Pacual, Eva Pascual i Miro. Warm Glass: A Complete Guide to Kiln-forming Techniques: Fusing, Slumping, Casting.

2.Cummings, Keith. A History of Glassforming. Soho Square, London: University of Pennsylvania Press, 2002.

3.Cummings, Keith. Techniques of Kiln-formed Glass. Soho Square, London: University of Pennsylvania Press, 1997.

4.Frary, Francis. Laboratory Manual of Glass-Blowing. New York, NY.: McGraw-Hill book Co., Inc., 1914

5.Kelley, Stephen J., ed. Standards for Preservation and Rehabilitation. Ann Arbor, MI: ASTM International, 1996.

6.Macfarlane, Alan and Gerry Martin. Glass: A World History. London, UK: University of Chicago Press, 2002.

 Stern, E.M., Toledo Museum of Art, ed. Roman Mold-blown Glass: The 1st Through 5th Centuries. Toledo, OH: L'erma di Bretschneider, 1995. New York, NY: Lark Books, 2005. 7.'All entries Alphabetically'. GlassFacts.info: A Daily Dose of Glass Art Knowledge.

8. Various dates given.<

9.'Art Deco Glass: Preservation of Historic Pigmented Structural Glass (Vitrolite and Carrara Glass)'. Old House Web. No date given.<

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