Arsenical bronze

Arsenical bronze was the Bronze Age before bronze—a copper-arsenic alloy that preceded the copper-tin bronze we associate with the era's name. For over a thousand years, arsenical bronze provided the hard, castable metal that pure copper couldn't, until tin sources and tin-bronze techniques replaced it. The alloy was bronze in function if not in modern terminology.

The adjacent possible for arsenical bronze lay in the ores themselves. Many copper deposits contain arsenic naturally; smelting such ores produced arsenical copper without intentional alloying. Early metallurgists noticed that some copper smelts came out harder than others and eventually traced the difference to ore composition. Intentional arsenical bronze followed—selecting arsenic-rich ores or adding arsenical minerals to copper melts.

Arsenical bronze's properties drove its adoption. Adding 2-8% arsenic to copper reduces melting temperature, improves castability, and hardens the final product. Tools and weapons of arsenical bronze held edges better than pure copper, could be cast into complex molds more easily, and work-hardened more effectively. These advantages made arsenical bronze the dominant alloy across the Middle East, Europe, and Central Asia from roughly 4200 BCE until tin bronze displaced it around 2000 BCE.

The arsenic came with costs. Smelting arsenical ores releases arsenic fumes; chronic exposure causes nerve damage, skin lesions, and characteristic lameness. Greek mythology's limping smiths—Hephaestus, Wieland—may preserve memory of occupational arsenicosis among Bronze Age metalworkers. The trade that produced superior metal also produced crippled craftspeople.

The transition to tin bronze reflected economics more than technology. Tin bronze is marginally better in most applications, but the critical difference was trade access. Tin deposits are rare and geographically concentrated—Cornwall, Afghanistan, Malaysia. Arsenical copper could be produced wherever arsenic-bearing ores existed, but tin bronze required long-distance trade networks. As those networks developed, tin bronze replaced arsenical bronze—not because it was superior, but because trade made tin available.

By 2026, arsenical bronze is metallurgical history, its era invisible in the terminology that calls the period 'Bronze Age' without specifying which bronze. But for the thousand years when it dominated, arsenical bronze built the civilizations that would eventually trade their way to tin.