Tin sources and trade in ancient times Bantu culture of Zimbabwe are known to have actively mined, smelted and traded tin between the 11th and 15th centuries AD . Tin deposits exist in many parts of South America, with minor deposits in southern Peru, Colombia, Brazil, and northwestern Argentina, and major deposits of exploitable cassiterite in northern Bolivia. These deposits were exploited as early as 1000 AD in the manufacture of tin bronze by Andean cultures, including the later Inca Empire, which considered tin bronze the "imperial alloy". In North America, the only known exploitable source of tin during ancient times is located in the Zacatecas tin
Chinese sun and moon mirrors most (1 part tin per 1 part copper) for "metallic mirrors", namely, the "jiànsuì" 鑒燧 "mirror-igniter" alloy (Hirth 1907: 217-218). However, these ratios are based on Chinese numerology instead of practical metallurgy. Beyond about 32% the alloy becomes excessively brittle, and increasing tin content brings no further advantages of any kind; this the Han metallurgists evidently knew. Indeed they knew much more, for they almost always added up to 9% of lead, a constituent which greatly improved the casting properties. Han specular metal is truly white, reflects without tinning or silvering, resists scratching and corrosion well, and was admirably adapted