Tin mining to trace metal content in the copper ore It was soon discovered that the addition of tin or arsenic to copper increased its hardness and made casting much easier, which revolutionized metal working techniques and brought humanity from the Copper Age or Chalcolithic to the Bronze Age around 3000 BC. Early tin exploitation appears to have been centered on placer deposits of cassiterite. The first evidence of tin use for making bronze appears in the Near East and the Balkans around 3000 BC. It is still unclear where the earliest tin was mined, as tin deposits are very rare and
Liberty Bell Museum found a considerably higher level of tin in the Liberty Bell than in other Whitechapel bells of that era, and suggested that Whitechapel made an error in the alloy, perhaps by using scraps with a high level of tin to begin the melt instead of the usual pure copper. The analysis found that, on the second recasting, instead of adding pure tin to the bell metal, Pass and Stow added cheap pewter with a high lead content, and incompletely mixed the new metal into the mold. The result was "an extremely brittle alloy which not only caused the Bell