Topics CoveredIntroductionWhy Was Bronze So Special?Durable Metals - Durable PracticesThe Evolution of MetallurgyAbout ASM International
The Bronze Age is a term used to describe and classify a period of time during which a development transition of ancient societies occurred inline with specific materials and practices prevalent at the time. For example, for many regions of the globe, the Bronze Age sits between the Stone Age and the more advanced Iron Age. Due to a naturally diffusion / spread of metallurgical knowledge, it is impossible to put specific dates for the start and finish of the Bronze Age (globally), however, it is widely accepted that the bronze age began approximately 3000 B.C. and lasted for approximately 1500 years.
The Bronze Age began when it was discovered that by combining two metals, or alloys, ancient man could create metals with much harder and stronger material properties than that of the original metals on their own. A discovery that many believe occurred near to the time that extractive metallurgy was developed.
|Created from content provided by ASM International in the book "Metallurgy for the Non-Metallurgist, Second Edition|
Editor(s): Arthur C. Reardon"
Why Was Bronze So Special?
The Bronze age was a step-change in the way that metals were created and applied.
A typical Bronze alloy of the early Bronze Age might contain approximately: 87% Copper, 10-11% Tin and minimal amounts <1% of iron, nickel, lead, arsenic or another. The simple addition of a Tin alloy to copper to create a much stronger and more chemically resistant metal was the crux of, and catalyst for the Bronze Age.
Amazingly, even though ancient man discovered in 3000B.C.that the simple addition of an alloy had a significant strengthening effect on the metal, it took nearly 4000-5000 years for the advent of Sterling Silver - a more modern application of the same method. Sterling discovered that by adding small amounts of copper (¡ 7.5%) to silver, he created a much stronger silver with no change in appearance, thus significantly improving the durability of Silver vessels, jewelry and utensils.
Durable Metals - Durable Practices
It's not just the metals of The Bronze Age that had durability. Many of the metallurgical theories and practices developed by ancient man still shape the way that we think about and use metals today. The persistence of ancient metallurgical practices is highlighted by the fact that an 11th Century 'recipe' for Bronze described as consisting of one pound copper and two ounces of tin (88% Cu and 12% Sn). This alloy is remarkably similar to the 87% Cu found in ancient bronze. Other publications suggest that a soft bronze or gun metal is formed when 16 parts of copper are mixed with one part of tin, and that a hardened gun metal, such as was used for bronze ordnance, is formed when the proportion of tin is approximately doubled. This hardened gun metal contains 88% Cu.
The Evolution of Metallurgy
The historical evolution of metallurgical practice from the production of copper to the production of bronze is difficult to trace. Certainly many of the early attempts to produce copper by heating copper sulfide ores in the presence of red hot charcoal produced arsenic-containing copper alloys. The mineral enargite is frequently found with other copper sulfide ores, and the reduction of this mineral would provide arsenic as well as copper. Such coppers (termed arsenical bronzes) are significantly stronger than arsenic-free copper. These first copper-tin bronzes probably resulted from the accidental inclusion of an alloy element through its presence in an ore body.
From a technological viewpoint, accidental improvements in the properties of metals is far different than the intentional mixing of two or more ores or refined metals to obtain an alloy with specific desired properties. However, by 3000 B.C., ancient metallurgists had learned to intentionally mix ores of copper and tin to produce bronze that is very similar in composition to some modern alloys. The alloys that were made from intentionally mixed ores marked the real onset of the Bronze Age. Mankind now had a metallic alloy that could be cast (i.e., poured as a liquid) or forged (hammered) to shape.
Bronze was significantly stronger than relatively pure copper and was useful both as a tool and as a weapon. Ancient Bronze castings often showed a high level of perfection particularly in Chinese foundry's in the 7th century B.C.
Low-tin bronze was probably produced because of the difficulty in locating good supplies of tin. Tin-rich ores were not as common as copper-rich ores. Frequently tin had to be transported over large distances. Because of these problems, bronze was an expensive material and unalloyed copper was probably used whenever practical.
Even during the Bronze Age there were material shortages, and tin was a critical material. Today, material shortages and in particular shortages in the production and supply of all kinds of metals has created a boom in the markets for metal recycling and the global price of scrap metal has increased drammatically.
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This Article was created from Material provided by ASM International in the book "Metallurgy for the Non-Metallurgist, Second Edition" Edited by A.C. Reardon.
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