Increase the liquidity of copper



Why is there lead in copper? The ancients made copper, not only using copper, but also adding tin or lead. The melting point of copper is very high, reaching 1083 degrees. At such a high temperature, when the copper water is poured out, its fluidity is very poor. "It's like making glutinous rice cakes during the New Year. It always sticks to the pot. After pouring it into the mold, it can't fill every place. The copper you get in the end may be a hole here and a hole there." And after adding tin and lead, It reduces the melting point of copper, improves the fluidity, and makes the copper ware smooth and beautiful.

Another effect of lead and tin is to increase the toughness of copper. Pure copper has good extensibility but not enough hardness, and the bronze sword is so thin but it is a murder weapon because tin is added to it.

Tin is volatile and cannot retain the isotopic characteristics of the mine period. Therefore, Jin Zhengyao believes that lead isotopes have become an important tool for judging the origin of cultural relics. "Any lead-containing utensils can be measured by this method." Through the textual research of lead isotopes, it can be known that the earliest glass in China came from the two river basins. In addition, uranium in ceramics also contains lead, which can be verified in the same way. In the verification of the authenticity of bronzes, the verification of lead isotopes is also useful.

Chemically, lead is known as a "tracer" metal that can track objects like a tracker, and other such metals include barium, which is commonly used in modern medicine to track stomach disorders.

However, lead isotopes have an Achilles heel: once things from different origins are mixed together, lead isotope measurements fail. "The higher the ratio of lead isotopes, the more single the source is, which is equivalent to coming from the same manufacturer, and the decrease in the ratio indicates that the source of lead entering the sediment has changed, or some deposits with a low ratio, especially some ultra-high ratios. Large-scale deposits produce lead isotope ratios that affect the entire world." Zhang Gan said.

In post-Industrial Revolution history, the lead isotope method basically failed, because global industrialization and trade globalization led to all mixing of lead sources. However, Zhang Gan believes that at the same time, the start of the industrial revolution can also be judged by the decline in the ratio of lead isotopes. For example, in their study, they found that the industrial revolution in China was later than that in the West. "A drop in lead isotope ratios is typical of the Industrial Revolution."

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