The earliest copper items that have been discovered are primarily located in West Asia. One example is the Javi Chermi area in Iraq, where copper decorations were found that date back to between 10000 BC and 9000 BC. Other examples include the Ali Kashgar area in western Iran, where copper ornaments were discovered between 9000 BC and 7000 BC, and the chayoni site in southern Türkiye, where copper needles and cones were excavated from about 8000 BC. These copper products were made from natural red copper, rather than copper that was obtained from smelting ore.
Human beings have embarked on a remarkable journey of discovery, gradually uncovering the secrets of copper. Initially, they utilized pure copper, melted it down, and extracted copper ore to ultimately obtain pure copper. This incredible process can be likened to the creation of a captivating space-time tunnel, meticulously constructed bit by bit using the enchanting properties of copper. Astonishingly, this endeavor doesn't end here. Humans, not content with their achievements, have progressed further to smelt bronze alloy, forging an even more extraordinary path of exploration. It is as if they are crafting a mystical passage through time and space, illuminated by the shimmering essence of copper in a magical world.
According to historical evidence, the earliest copper smelting process in the world can be traced back to Shaanxi, China. Archeologists uncovered a brass sheet and a brass tube at the Jiangzhai Cultural Site in Lintong, Shaanxi Province. These artifacts have been dated to approximately 4700 BC. Interestingly, the Shanghai Light Source recently conducted X-ray fluorescence surface scanning analysis on the brass sheet. The study showed that the zinc content in different areas of the brass sheet was unequal. Moreover, sporadic points containing traces of lead were identified. These results are consistent with the use of hot forging or solid reduction techniques for smelting natural metals. It proves that our ancestors utilized these methods when inventing metal casting.
During the Ming Dynasty's Jiajing period, brass coins were first introduced in China.
In the Western Han Dynasty, Dongfang Shuo wrote the Shenyi Sutra Zhonghuang Sutra, which mentioned the word "brass" for the first time. According to the text, there was a palace in the northwest region, and its walls were made of brass. This palace was known as the emperor's palace.
The term "brass" mentioned here pertains to a specific type of copper alloy that needs to undergo testing. In the historical text called "The New Book of Tang · Shi Huo Zhi," there are also mentions of "bronze" and "brass," which respectively denote the color of the ore and the outcome of the smelting process. Moreover, when we talk about the various names given to different pits and the abundant yet straightforward mountains, it signifies the purification of copper through the intense heat of fire. Thus, this information provides the basis for generating a closely related content.
During the Ming Dynasty, the term "brass" specifically referred to a copper-zinc alloy. Historical evidence of this can be found in the "Ming Huidian," where it states, "An example from the Jiajing era showcases Tongbao coins totaling six million wen, made from a brass alloy weighing 47272 jin." A careful examination of copper coin compositions from the Ming Dynasty reveals that the specific type of copper alloy mentioned in the Ming Huidian appeared much later than other copper alloys. This delay resulted from the challenges associated with obtaining zinc, a crucial component in creating brass.
At very high temperatures between 950 ℃ - 1000 ℃, zinc oxide can be transformed into metal zinc quickly. However, since liquid zinc boils at a lower temperature of 906 ℃, the produced zinc metal exists as vapor. To obtain metal zinc, a specific condensing device is necessary. When dropped to normal temperature, the reaction goes in reverse, and the steam zinc is exposed to carbon dioxide within the furnace and changes back into zinc oxide once again. This unique process is why the use of metal zinc was slower to develop compared to other metals, like copper, lead, tin, and iron. This is also one of the causes as to why brass coinage was introduced later than other forms of currency.
During the Shang and Zhou Dynasties, bronze ware had a very low zinc content. Similarly, coins from the Western Han Dynasty and Xinmang did not contain much copper, zinc and licorice. While some coins did contain 7% zinc, this was not a widespread occurrence and their zinc content was still much lower than what we now know as brass zinc content (15% to 40%). It is assumed that these copper zinc alloys were produced in the Han Dynasty when copper zinc intergrowth ores were used in "Jishan Coin Casting". Certain mines in Shandong Province were found to be rich in copper zinc intergrowth ores, causing the copper to contain some zinc after smelting. During the Tang Dynasty, the content of zinc in coins remained constant due to standardized coin casting materials.
