An important development of the Bronze Age was the evolution of metallurgy, which resulted in the discovery of bronze. Some metals, notably tin, lead, and (at higher temperatures) copper, can be recovered from their ores by heating rocks in a fire or blast furnace, a process known as smelting. The first evidence of this extractive metallurgy dates from Serbian sites in the fifth and sixth millennia BC.
Around the fourth millennium BC in Sumer, India and China, it was discovered that combining copper and tin created a superior metal, an alloy called bronze. This discovery marked the beginning of the Bronze Age, allowing people to create metal objects that were heavier than previously possible. Bronze tools, weapons, armor, and building materials such as decorative tiles were more durable than their stone and copper predecessors.
Bronze was originally made from copper and arsenic, forming arsenic bronze, or from natural or artificially mixed ores of copper and arsenic, with the earliest known artifacts coming from the Iranian plateau in the fifth millennium BC. Only later, around 3500 BC, did tin become the main non-copper ingredient in bronze. Tin bronze was superior to arsenic bronze because the alloying process could be more easily controlled, and the resulting alloy was stronger and easier to cast. In addition, unlike arsenic, metallic tin and the fumes from tin refining are non-toxic. Two forms of bronze were commonly used in the Bronze Age. “Classic bronze,” about ten percent tin, was used in casting. “Soft bronze,” about six percent tin, was hammered from ingots to make sheets. Bladed weapons were mostly cast from classical bronze, while helmets and armor were hammered from soft bronze. The flag pictured below was also probably hammered from soft bronze.
Large hoardings of bronze artifacts have been discovered in many parts of the world, suggesting that bronze also represented a store of value and an indicator of social status. In Europe, large hoardings of bronze tools have been discovered, usually axes with little or no signs of wear. Axes were the most valuable tools of the period.
Although bronze was originally used to make weapons, metalworkers soon applied the alloy to the production of art. One of the oldest and most common methods of making bronze sculptures is the lost wax process, which creates hollow, unique sculptures in any shape the artist chooses. The Dancing Girl (c. 2500 BC), from Mohenjodaro in the Indus Valley, is probably the world’s first bronze statue. Although she is in a standing position, she was named the Dancing Girl, suggesting her profession. It is one of two bronze works of art found at Mohenjodaro that show more flexible features compared to other more formal poses. The girl is naked, wearing a series of bracelets and a necklace, standing in a naturalistic position with her right hand on her hip and an object resting on her thigh in her left hand.
The Unetice culture emerged at the beginning of the Central European Bronze Age (2300-1600 BC). The culture is distinguished by distinctive metal objects, including ingot torques, flat axes, flat triangular daggers, bracelets with spiral ends, disk and paddle-shaped pins, and curling rings, which are common over a wide area of Central Europe and beyond. An interesting mixed-media object from this culture is the Nebra Celestial Disc (c. 1600 BC), which consists of blue-green patina inlaid with golden symbols. These symbols have been interpreted as the sun or full moon, the lunar crescent, and stars (including a cluster interpreted as the Pleiades). The two golden arcs on the sides, indicating the angle between the solstices, were added later. The final addition was another arc at the bottom, surrounded by multiple strokes (of uncertain meaning, variously interpreted as a solar barge with numerous oars, like the Milky Way, or like a rainbow). Probably made with hammers, the disk is possibly an astronomical instrument as well as an object of religious significance.