Metallurgy through the Ages

Overview

Over a period of thousands of years, humans learned to identify, extract, blend, and shape metals into tools, ornaments, and weapons. The ability of metals to alter the wealth, power, and culture of societies is so profound that the Bronze Age and the Iron Age label distinct eras in human development. Metallurgy makes the current Information Age possible and continues to shape our lives.

Background

Metals have shaped history—magnifying our efforts, providing leisure time, and creating empires—because metals allow us to shape our environment like no other materials. Ironically, the first recognized metal, gold, is unchanging and nearly useless. Gold exists in an almost pure state in nature. It does not rust or corrode, and, undoubtedly, it gleamed out from rocks or streambeds, catching the attention of humans in prehistoric times. Gold can be easily shaped, but it is so soft that it cannot be used for weapons or tools. The most useful material of this early time was stone, so this period is not known as the Golden Age, but the Stone Age. The only metal artifacts of this age are beautiful ornaments and simple utensils, such as cups and bowls. Still, gold did teach some fundamental principles of metallurgy that would become useful in later times: discovery (finding and recognizing a metal in nature), concentration (in the case of gold, by cold hammering smaller pieces into larger pieces), and shaping (working the metal into a desired form).

It was copper, beginning in about 4000 b.c., that allowed humans to extend the techniques of metallurgy. Smelting, the use of heat to extract metal from ores, may have been discovered accidentally by potters. Kilns are hot enough to form of copper if the malachite and other copper-containing minerals are present during the firing process. Copper is too brittle to be cold hammered, but it could be hot hammered into sheets. Concentrating copper would have required the melting together of smaller pieces. Copper is a relatively soft metal, but it can be cast into tools and weapons. Copper became the starting point for the invention of alloys. This might have been helped out by natural contamination, mistakes (such as confusion caused by the similarity of the flames from copper and arsenic), or scarcity of ores. Whatever the source, it led to the creation of bronze, the metal that ended the Stone Age, in about 3000 b.c.

The first bronze was arsenic-based, but true bronze, an alloy of tin and copper, can be traced to the Sumerians in 2500 b.c. It was initially made by smelting different ores together, rather than by combining pure metals. Bronze is much harder than copper. It was widely adopted and made into weapons, tools, such as axes and scythes, and ornaments.

The dominance of bronze ended with the production of iron, a harder and stronger material. Iron began to replace bronze in about 1200 b.c. Iron oxide was used as flux in the smelting of copper to help the metal agglomerate. As temperatures in kilns were raised to accommodate new ores, this flux would leave iron residues. The first smelting of iron probably occurred in Anatolia, part of modern Turkey, in 2000 b.c. But pure iron is fragile, and the first uses of iron were generally ornamental. A breakthrough occurred with the development of coking, which allowed melting at lower temperatures and provided a harder, more durable version of the metal (really a carbon-iron alloy, steel). Iron smelting appears to have developed independently in both China and sub-Saharan Africa. In fact, there is evidence of smelting near the African Great Lakes as far back as 800 b.c. This technology began spreading throughout sub-Saharan Africa in about a.d. 100 with the migration of Bantu-speaking tribes, and continued until about a.d. 1000.

The working of iron began with wrought iron, which was simply sequential hot hammering, quenching (quick cooling in water to change the crystal structure), and reheating (annealing) of "blooms" (spongy, impure globules of iron). The result was strong, tough, and workable steel. The Iron Age lasted over 1,000 years in Europe, and Iron Age cultures were still dominant in some areas of Africa into the nineteenth century.

Impact

The chief value of metals is derived from their physical properties. Metals are malleable and can be melted together so small amounts can be combined and worked or cast into useful forms. Metals are hard, strong, and can be flexible while resisting permanent distortion, so they can be used for shields, blades, and springs. Different metals and nonmetals can be combined as alloys, blending and transforming their characteristics to customize materials to specific tasks. In recent times, other properties of metals—their ability to conduct electricity, their biological roles (such as in enzymes), their properties with light (paints), their radioactive properties (uranium)—have kept them at the leading edge of our technology and have made the principles of metallurgy discovered in ancient times even more essential.

Metals provide exquisite control over the use of energy. A blade concentrates and directs forces that can be used to plow a field, shave a man's face, or kill an enemy in battle. A spring stores and redistributes mechanical energy. A pipe directs the flow of material. Metal technology also provided the first skills in transformation of materials that led to the development of chemistry. The alchemist's hope of changing lead into gold has been surpassed by our control of materials at the atomic scale, control that reaches back to the lessons of purification, recombination, and qualitative analysis that came from metallurgy. When the concept of chemical elements arrived, metals helped populate the first periodic tables.

A curious side effect of the development of metal alloys was the discovery of the principle of buoyancy. Because it was possible to mix silver with gold, the king of Syracuse asked Archimedes (287?-212 b.c.) to find out if his new crown was really pure gold. Archimedes found that he could determine the volume of the crown by displacing water. A similar volume of pure gold should weigh the same as the crown, so any discrepancy would point to the use of an alloy. The famous cry of "Eureka!" indicated not just that Archimedes had found an answer to a royal problem, but that he had discovered an important principle of physics.

The development of metallurgy had a profound effect upon the environment and the relationship between humans and nature. Wherever iron was introduced, deforestation and an increase in agriculture followed. Mining operations leached acids and toxic minerals, including mercury and arsenic, into nearby water. Waste products fouled the land and the air. The smelting of lead in 150 b.c. Rome produced clouds of toxic gas so extensive that a record of the air pollution is evident today in ice deposits in Greenland.

Metals are of such social and historical significance that two eras are named for them, the Bronze Age and the Iron Age. As an alloy, bronze was the first truly artificial material. With a wide range of characteristics that could be controlled, bronze was used for tools, utensils, and uniquely expressionistic ornaments. Bronze also made the sword possible, the first specialized tool for combat. Before the Bronze Age, warfare was informal and disorganized. With the introduction of bronze, artisans who created weapons and defensive armaments (including shields) came to be. Campaigns of conquest became possible and fortifications were built to defend newly arising cities, trade routes, and the sources of tin and copper ores. Bronze was so versatile and central to economies that, even after effective production methods for iron were developed, it took centuries for the new metal to supplant bronze.

Eventually, iron replaced wood, flint, and stone, as well as bronze. Its use was wider and more intensive than bronze, extending and revolutionizing agriculture and putting high-quality weapons into the hands of large masses of people. Iron resources changed trade routes. In particular, trade between northern Europe and the people of the Mediterranean withered, making the regions more culturally distinct. Iron also forged connections between tribes, and it is in the Iron Age that the roots of most modern European nations are found. Iron enabled large-scale migration, often driven by the march of powerful armies. While the bronze sword was a stabbing tool, the iron sword was a slashing tool, making equestrian warfare possible and allowing extended, large-scale battles. Iron also improved the use and durability of wheels, adding chariots to combat. The first tires were hot bands of iron wrapped around wood that shrunk upon cooling for a tight fit.

Settlements became more permanent during the Iron Age. Both the increased size of human societies and the need for defense led to new roles. For the first time, there is evidence of significant stratification across different cultures, with a well-fed class that did not do extensive, hard labor, and those with more limited diets who regularly took on the backbreaking work. The Iron Age was an age of kings and heroes, and this is reflected in the poetry and religion of the times.

PETER J. ANDREWS

THE THREE AGES SYSTEM

The system of three ages provides historians with a yardstick for measuring ancient and prehistoric levels of technological development according to the materials from which a society makes it tools. Although years are assigned to certain ages, these dates reflect the time when the most advanced civilizations—primarily those of the Near East, India, and China—evolved to the next level of development. Technological evolution was much slower in areas where environmental conditions forced the populace to maintain a subsistence lifestyle.

The Stone Age is divided into Paleolithic or Old Stone Age, which roughly corresponds to the geological Pleistocene Age (1.8 million-10,000 years ago); the Mesolithic or Middle Stone Age, from the end of the last Ice Age to between 8,000 and 6,000 years ago; and the Neolithic or New Stone Age, which began thereafter. Dates for the last of these vary widely: the cultures of the Americas, for instance, did not enter the Neolithic Age until c. 1500 b.c., by which time the Near East had long since entered the Bronze Age. The latter has been divided into an Early Bronze Age (c. 3300-1950 b.c.), Middle Bronze Age (1950-1539 b.c.), and Late Bronze Age (1539-c. 1200 b.c.) Again, these dates are for the Near East: the cultures of the Americas did not begin to use bronze tools until c. a.d. 1100. Finally, the Iron Age is divided into Iron Age I (1200-950 b.c.) and Iron Age II (950-586 b.c.)

Technological development does not always reflect advancement in other areas: thus the Nok people of what is now Nigeria developed ironworking in about 1000 b.c., but lacked a written language or cities. The Aztecs, by contrast, had writing, cities, sophisticated engineering methods, and a highly organized society—but they never entered the Iron Age.

JUDSON KNIGHT