A research article authored by Research Scientist Keishiro Azami as the first author and Principal Research Scientist Yasuhiro Kato as a co-author has been published in Scientific Reports (Springer Nature).

From the 9th to the 15th centuries, the Khmer Empire flourished in the region centered on present-day Cambodia. The empire constructed numerous monuments, including Angkor Wat, and ironmaking slag—glassy by-products generated during ore smelting—has been often discovered at and around Khmer monuments.

In this study, we analyzed the chemical compositions of slag and ore fragments collected from slag mounds in northern Cambodia to clarify the temporal changes in ironmaking technology between the 10th and 14th centuries. The results revealed that, from the late 10th to 13th centuries, during the peak of the Khmer Empire, laterite and umber were used as iron ores, while hydrothermal manganese oxides and sulphides were added as aditives. These ores originated from hydrothermal deposits formed on the ancient seafloor distributed around the study area. The addition of manganese oxides and sulphides is inferred to have enabled the efficient production of high-quality iron.

In contrast, by the 14th century, when the Khmer Empire declined and the study area came under foreign occupation, ironmaking became simpler and less efficient—using only laterite and magnetite as iron ores—indicating that the advanced ironmaking techniques had been lost. This study provides the first evidence linking changes in ironmaking “recipes” to the rise and fall of the Khmer Empire.

The full paper is available at the link below:

https://www.nature.com/articles/s41598-025-27581-x