Lead or Mercury, haifuki-hō or plata de azogue: The Environmental Dilemma in the History of Silver Refining

In the sixteenth century the Spanish Empire would find itself owner and conqueror of the largest deposits of primary silver and mercury in the world, a geopolitical conjunction which would lead to the use of mercury at an industrial scale in the production of plata de azogue (silver by mercury) from silver sulfide deposits found in the Americas. Thus, two refining processes, the millennia-old two-stage smelting process based on lead and high temperatures, and the upstart based on mercury sine igne (without fire), came to share in nearly equal parts the aggregate global production of silver from the sixteenth to the final decade of the nineteenth century. These processes relied on the extensive use of two of the heavy metals most toxic to humans, and their anthropogenic emissions to the environment have caused impacts lasting over subsequent centuries. However, the successful use of haifuki-hō (smelting-cupellation process) in Japan to produce silver from silver sulfide ores with 0.2 percent silver content demonstrates that the extensive use of mercury by Spanish refiners in the New World was not the consequence of the geochemistry or silver content of the ores.