Archaeologists and metallurgists have found, inside one of the Bronze Age amulets found in Pakistan, the first unambiguous traces that mankind mastered the secret of molding already six thousand years ago, according to an article published in the journal Nature Communications.
Humanity first met with metals and realized their useful properties a long time ago, back in the era of the primary colonization of the world outside Africa, about 40 thousand years ago. However, the ability to use metals for the manufacture of tools and the secrets of their smelting appeared much later, during the so-called Chalcolithic, the Copper-Stone Age, which began about 7-5 thousand years ago.
According to Mathieu Thoury from the University of Versailles in Gif-sur-Yvette (France), the first tools and jewelry made by man were rather primitive and "piece" things, more like stone tools than modern or medieval swords, scythes, plows or belt buckles. Therefore, most scientists believed that "advanced" metallurgical techniques such as molding casting appeared much later.
Turi and his colleagues found that this was not really the case by studying one of the oldest examples of metallurgical art on Earth - a copper amulet found in Pakistan at the Mergarh site in Baluchistan in 1974. This settlement is the oldest trace of civilized society and agriculture in Hindustan, and its inhabitants are considered the progenitors of the famous and mysterious Harappan civilization.
Scientists have long been interested in how such plaque amulets were made, very similar in shape and size and of unusually high quality for their historical period. French archaeologists tried to find an answer to this question by involving physicists in the analysis of these artifacts and using the methods used today in the analysis of proteins or carbon nanotubes.
As scientists explain, irradiation of any material with powerful laser beams leads to the fact that its atoms absorb some of the radiation energy and then gradually re-emit it at other wavelengths. The frequency of these waves and when they appear depends on the structure and composition of the molecules that have absorbed the light, which makes it possible to very accurately determine the composition of the substance "bombarded" by the laser from the spectrum of this repeated radiation.
Using this technique, the scientists discovered that the wheel-like plaques from Mergarh contained unusual cobweb-like deposits of copper oxide within the “spokes” and “rim” of this copper wheel, spread over the entire surface of the artifact. Such compounds, as physicists explain, are traces of contact of copper with organic matter, and, according to archaeologists, indicate an unusual method of making this amulet for that time.
According to Turi and his colleagues, this artifact was made using a revolutionary method for that time, the so-called "investment casting", the oldest molding method on Earth. Its main advantage is that it allows the manufacture of very complex three-dimensional structures, which are a single piece of metal, which cannot be realized by pouring open forms of stone and clay.
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A key role in this process was played by wax, from which ancient metallurgists sculpted a model of jewelry. Then they covered it with clay and fired the resulting structure in an oven. All the wax flowed out, and the clay was baked, which turned it into a peculiar form, which the ancient inhabitants of Mergarh then used to make an amulet, pouring it with pure copper (which was also a great innovation).
Given the age of the artifacts from Mergarh, these plaques are by far the oldest example of molding casting on Earth. Thus, we can say that Pakistan is the birthplace of "advanced" metallurgy. Scientists believe that later the traditions and metallurgical secrets of Mergarh spread throughout the Middle East, giving life to a whole culture of making unusually beautiful oriental metal jewelry with an extremely complex shape.
Casting process, diagram of the authors of the article
L. Bertrand, T. Séverin-Fabiani, S. Schoeder // IPANEMA CNRS MCC UVSQ / Synchrotron SOLEIL