Smelting of Bronze

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Introduction

Though a lack of technology plagued the Classical Ages of Europe and Asia Minor, one development out-shined the few already existing. Copper was being used by early civilizations as a material for tools by approximately 5000 B.C.E. and tin was extracted from mines by about 2000 B.C.E. Then, by 1500 B.C.E., ancient societies began to make the very complex and intriguing alloy of bronze. Bronze, a compound made of about 90% copper and 10% tin, was actually made far earlier than the 16th Century B.C.E. However, historians believe that this more primitive system was a coincidence of the copper ores contaminated by the tin, not a fully understood process of refining and melting rocks at a certain ratio to make a far superior material for weapons, armor, and trade goods. It is curious to note from studies and excavations that although the wheel, a tool we consider to be extremely simple, originated in India and spread to the rest of the world while bronze developed almost simultaneously, globally.

History of Smelting

Generally, historians and archaeologists agree that most smelters were the chiefs or leaders of a group of people. As the video below dictates, this form of metalworking was seen by the general public as a "rebirth", almost a magical event. As Professor Andrew Sherratt explains, a higher-ranked person would be tied into the process as a general rule. Although today we look at the lower-class as working at the smelts, the older civilizations saw this job as a highly sophisticated and godly responsibility.



In this lower video, Eddie Daughton explains also the significance of smelting in ancient society. He shows another how the smelting was actually done in earlier eons. The smashing of the ore, the fire complete with bellows, and the casting are all perfect examples of how this is completed. Listen as he discusses the power of smelting, and the general concept of, bronze:


Production




The Chemistry

Most bronze that is created is not of a pure mixture. Usually a smelting of 90% copper and 10% tin results in the best goods, but zinc and other contaminating ores may be included as part of those percentages. The equation to create a more realistic form of bronze, compared to a clean-cut ratio of copper and tin, is known to be:

1173° Kelvin + 300 kg C (charcoal) + 30 kg SO (sulfide ore)* + 0.11 kg Sn (tin) --> ~ 1 kg bronze
*(Copper is formed from the remains of the process when charcoal is used to burn the sulfide ore)

There are two kinds of bronze compounds, each named after the main ingredients in "regular" bronze. The first is known as copper bronze and the second as tin bronze. The copper variant is tougher to work with in the forge, requiring 1257° Kelvin to mold, while tin bronze is not as difficult to work with, and melts at 1123° Kelvin. One can safely assume that "copper" refers to a higher ratio of copper, and "tin" refers to a higher ratio of tin.

The most commonly used tin oxide during the smelting process is known as cassiterite. The ore appears as a very distinctive dark colored, or even black, sand grain. This peculiar powder-like substance is a remnant of weathered down granite, along with clay and other items. Some researchers speculate that potters had cassiterite contaminate their clay pottery from such a natural process, creating the knowledge and production of bronze further in the future. Unlike pottery, cassiterite will melt at only 773° Kelvin, allowing for it to be noticed when placed in a kiln. Thus, the cassiterite may, "perhaps [have been] accidentally smelted to tin".

The Cost of Science

Any field of knowledge, be it philosophical or mathematical, requires some payment from the materials of the world. Unfortunately, even in the more ancient ages of human civilization science has taken a toll on our resources. During the Bronze Age, the Greeks realized the troubling truth that their islands' main industry of metal-making was dying. As the name implies, that era was based principally on the trade and creation of bronze materials. Smelting, however, needs an extraordinary amount of fuel to power the production of the metallurgy. 300 kg of charcoal smelted with 30 kg of sulfide ore produce a single kilogram of copper. Besides that terrible number, 12 to 20 cubic meters of wood creates only a single ton of the charcoal needed for the smelting process. Plato has been quoted as saying:

"...a mere relic of the original country [of Greece].... What remains is like the skeleton of a body emaciated by disease. All the rich soil has melted away, leaving a country of skin and bone. Originally the mountains of Attica were heavily forested. Fine trees produced timber suitable for roofing the largest buildings: the roofs hewn from this timber are still in existence."

Sources


"Chapter 4: The Bronze Age." MyGeologyPage. Web. 03 June 2010. http://mygeologypage.ucdavis.edu/cowen/~gel115/115ch4.html.

Amlwch History. Web. 03 June 2010. http://www.amlwchhistory.co.uk/bronze.html
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"Science - Engineering: Metal Works." IHMC CmapServer V5.00, Concept Maps. Web. 03 June 2010. http://cmapspublic2.ihmc.us/rid=1101134910296_1913677506_1084/Science - Engineering Metal Works.htm .

"Cyprus Peak Wood Experience Knock Props From Beneath Culture." Miller-McCune Online. Web. 03 June 2010. http://www.miller-mccune.com/science-environment/peak-wood-and-the-bronze-age-14363/.

Amos, H. D., and A. G. P. Lang. These Were the Greeks. Amersham, Bucks.: Hulton Educational Publications, 1979. Print.

Nardo, Don. Ancient Greece. San Diego, Calif.: Greenhaven, 2001. Print.