Ever since China’s Terracotta Army was discovered in 1974 it has been thought that the Warriors weapons, many of which are bright and sharp, had been preserved by an advanced form of chromate conversion coating technology (CCC). This belief was supported by the detection of chromium traces on the surface of the weapons.
Professor Marcos Martinon-Torres led a team at University College London (UCL). They examined the weapons lacquer and soil from the site and conducted CCC and accelerated ageing. The results have shown that the surface chromium present is correlated with artefact type and uncorrelated with bronze preservation. The lacquering used extensively to cover the figures and wooden parts of weapons is rich in chromium.
Professor Martinon-Torres concluded that the chromium enrichment, detected on the surface, is not the consequence of a deliberate treatment, but a post depositional contamination. Also that the source of the chromium is lacquer, used throughout the site. The soil from the site is moderately alkaline ph with small particle size.
In summary, the lacquer, soil type and bronze composition, combined to lead to the remarkable preservation of weapons, which had laid undisturbed for over two millennia.