- Archaeological News
-
Image Credit: Saigen Jiro, CC0, via Wikimedia Commons
New Ways to Protect Metal Artifacts Inside Ancient Japanese Tumuli
A new study published as an article in press in npj Heritage Science examines how metal artifacts may corrode when preserved inside ancient burial mounds, offering new insights for the future in-situ conservation of archaeological materials. The research focuses on Japanese tumuli, known as kofun, many of which contain stone chambers and burial goods made of iron and bronze.
Japan has around 200,000 tumuli dating mainly from the Kofun period, which began in the mid-3rd century AD and continued until the end of the 7th century AD. Many of these monuments remain unexcavated, and there is growing interest in preserving artifacts inside their original burial environments rather than removing them. This approach helps maintain archaeological context and reduces the need for costly long-term storage and conservation after excavation.
To better understand the risks facing buried metal artifacts, researchers carried out experiments inside a simulated tumulus at Kyoto University. The model included an earthen mound and a stone chamber, recreating key features of ancient burial mounds. Sensors were installed to monitor environmental conditions such as temperature, humidity, oxygen and carbon dioxide levels, soil moisture, rainfall, and surface wetness. Special corrosion sensors were also placed in different positions, including inside the chamber, near the ceiling, under protective covers, and in burial soil.
The results showed that surface wetness was the most important factor affecting corrosion. Temperature and oxygen levels did not show a clear direct relationship with corrosion rates. Instead, the duration and extent of water films on metal surfaces played the main role. In summer, corrosion was linked to persistent moisture caused by condensation and rainwater dripping from the chamber ceiling. In winter, corrosion proceeded more slowly and was mainly associated with intermittent drops of condensed water.
The study also found that metal placed in moist burial soil corroded more strongly than metal exposed in the chamber air. Rainfall increased soil moisture and expanded the wet surface area around the sensors, accelerating corrosion. Chemical elements detected on the sensors suggest that water moving through the mound and chamber can carry dissolved materials that further influence corrosion.
Based on these findings, the researchers propose two practical strategies for preserving metal artifacts in place. The first is to improve the thermal insulation of the mound in order to reduce temperature differences that cause condensation. The second is to modify mound structures where necessary to limit rainwater infiltration into the stone chamber.
Published on: 25-05-2026
Edited by: Abdulmnam Samakie
Source: npj Heritage Science
