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Arts & Communication Safeguarding Sinauli’s royal chariot discovery

the course of several millennia, the wooden materials have copper artifacts can develop a natural patina or corrosion
completely transformed into mud. The transformation, product on their surface. Metals are thermodynamically
where organic matter converts into clay minerals, is a unstable and release free energy to attain a stable state,
complex process that occurs over a long period of time resulting in surface changes as they react with various
under specific environmental conditions. When wood is environmental agents, a process known as corrosion.
exposed to moisture, microorganisms such as fungi and Corrosion is a chemical or electrochemical process
bacteria begin to break down its organic components, where metal is converted into its mineral form, and it is a
including cellulose and lignin. This initial decay weakens continuous process.
the wood structure. As the decay progresses, soluble The corrosion mechanism of pure copper metal under
components of the wood, such as sugars and other organic the earth involves a combination of chemical reactions with
molecules, leach out into the surrounding environment. various components present in the soil or surrounding
This leaching can contribute to the formation of a muddy environment. The patina forms through a combination of
or sludgy substance around the decaying wood. In copper oxide, copper carbonate, and other copper salts.
environments with high levels of clay minerals, such as The primary corrosion process is known as oxidation,
certain soils or sedimentary environments, these leached where copper reacts with oxygen and other substances
organic compounds can interact with mineral particles, to form corrosion products. A simplified overview of the
leading to the formation of new clay minerals. This process, mechanism is given below:
known as mineralization or pedogenesis, involves complex
chemical reactions that transform the organic matter into Formation of copper oxide:
inorganic mineral structures. Over time, the muddy or Copper + Oxygen + Water→ Copper (I) oxide+
sludgy substance surrounding the decaying wood becomes Hydrogen ions
compacted, further enhancing the transformation into
a solid, clay-rich material. 9,10,15 EDXRF analysis has also Formation of copper carbonate:
been performed on the mud portion transformed from Copper (I) oxide + Carbon dioxide + Water→ Copper
wood as well as on the original mud bricks recovered from carbonate + Hydrogen ions
the Sinuali excavation (Figures 8 and S2). Investigating The copper carbonate formed in this process is typically
the variation in the composition of metals and wood green in color.
transformed into mud will be a focal point of our
upcoming research. We plan to employ more sophisticated The problem of corrosion is severe in unearthed
techniques and compare our findings with those of similar decorated copper inlay and thick plates of royal
copper objects. The analysis will also examine impurity chariot because cuprous ions rapidly oxidize to cupric
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concentrations and specific areas associated with the ions, influenced by various factors. The symbolic
relevant historical period. This comprehensive approach mechanism is:
aims to provide a nuanced understanding of the material Cu → Cu + e
+
transformation, shedding light on the broader historical + ++
and archaeological context. Cu → Cu + 2e
The semi-circular wooden platform of the ancient royal O +2H O+ 4e→ 4OH -
2
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chariot was covered with thick metal plates, approximately 99% The unearthed copper plates and decorated inlay
copper (Supplementary Figures S1 and 2), as analyzed using work of the royal chariot exhibit patina or encrustation of
the non-destructive hand-held EDXRF technique (Figure 7). chlorides, oxides, and copper carbonates on the surface.
Pure copper was commonly used for inlay work in ancient The copper metal from the excavated royal chariot
royal-class artifacts due to its malleability, conductivity, and underwent scientific treatment, involving both mechanical
durability. The chariot was heavily decorated with copper and chemical methods. This treatment, guided by the
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inlays, hence its designation as the royal chariot. The platform expertise of archaeological chemists, aimed to remove the
was constructed using copper pipes to secure the side panels corrosion products and hazardous compounds present
and a pipe to connect the canopies and inner-outer edges within the corrosion crust.
of both solid wheels. Triangular copper inlays, arranged in To prevent potential issues in the future, comprehensive
three rows extending from the central hub to the outer rim, documentation of every step was carried out. After the
adorned the wheel, pole, and yoke. removal of straps and slings from the royal chariot, it

This chariot was discovered at a depth of about 1.5 m was delicately brushed to eliminate dust and dirt, and
beneath the alluvial soil in agricultural fields. Over time, detailed photographs of its surface were taken. A surface

Volume 2 Issue 4 (2024) 7 doi: 10.36922/ac.2437