A new photoluminescence technique has helped archaeologists uncover the secrets of a 6,000-year-old amulet found in Pakistan three decades ago. The object is thought to be the earliest created with wax casting – a method once used to duplicate metal sculptures cast from an original sculpture.
The amulet was unearthed at the site of Mehragarh, a Neolithic site located in Balochistan, western Pakistan. It is often referred to as a crucible for technological innovation during Neolithic times in ancient South Asia, as people living there innovated in areas as varied as pottery making, textiles and even dentistry.
When the amulet was discovered in 1985, studies showed that the objects complexity and lack of symmetry suggested it was probably made using wax casting. However, evidence to back this hypothesis up was limited.
Furthermore, researchers were surprised to discover that the amulet was only made up of copper elements, which didnt seem to match what they had observed via conventional microscope.
Scientists had reached the limits of what they could learn from the amulet with traditional imaging techniques, and could not solve the paradoxes regarding how it had been manufactured. We have designed a full-field photoluminescence approach to look at the objects structure and composition in greater details. This has allowed us to infer what the amulet was made of when it was first created six millennia ago, based on what it is made of now, physicist Mathieu Thoury of the synchrotron SOLEIL lab in France told IBTimes UK.
The results that he and his colleagues achieved from this technique are published in the journal Nature Communications.
Pure copper and lost wax
The full-field photoluminescence technique works by shining light on the objects that researchers want to analyse. They can then determine the spectrum re-emitted by the sample. This enables them to distinguish between the different elements constituting the amulet. In this case, they observed that two copper oxides were present in the sample.
The same physical and chemical patterns appear to be present across the surface of the sample. This indicates that the amulet was probably cast as a single piece – giving credit to the theory that it was created using the wax-casting technique. Additionally, the presence of the copper oxides suggests that amulet was made from a very pure copper melt. It would have then been poured into a prepared clay mould using wax casting – the earliest evidence of the use of such a technique.
The use of pure copper may indicate that this object had a particular status, it was maybe used for religious or ritualistic purposes. The fact the metallurgists used the technique so early on confirms the impressive capacity that people living at Mehragarh had to innovate – and it really was an important innovation considering the technique is still used today, nearly 6,000 years after the amulet was created, Thoury says.
The full-field photoluminescence technique thus allowed scientists to uncover the secrets of how the amulet was manufactured. It identifies a significant technological innovation that occurred 6,000 years ago. The team now hope their method could be applied in a variety of fields – not only archaeology but also geophysics, engineering and environmental sciences.