Metal artifacts made of iron, gold, silver, copper, and their alloys include Buddha statues, ornaments, weapons, harnesses and various other cultural assets. Metal artifacts are subject to corrosion and damage, and such deterioration leads to disfiguration and changes of the surface. Conservation treatment aims to restore the original form, color, and surface condition of such works. Treatment is conducted after determining the most appropriate conservation method following a variety of examinations to study the condition of the artifact in question. Conservation processes may reveal patterns, decorations, and techniques employed in the creation that may have been hidden due to damage. This will provide important information in studying ancient metal artifacts.
Metal artifacts, especially those excavated, show various traces of corrosion depending on the environment of burial as well as their composition. They may be vulnerable to additional corrosion, cracking, and peeling due to rapid changes in the environment after they have been unearthed. Also, damage and corrosion can occur from mishandling and improper storage, while excessive conservation treatment or the use of inappropriate restoration materials may also be the cause of further damage.
Example of corrosion of artifacts resulting from sudden environmental changes after excavation
Losses resulting from corrosion
Damage caused by mishandling
Re-corrosion caused by improper conditions in storage environment
One of the studies conducted prior to the conservation process involves the use of X-rays to examine the extent of corrosion and damage, production techniques, presence of patterns, and traces of damaged and restored parts. X-ray imaging provides a variety of information including the condition of the artifact that cannot be visually confirmed due to heavy corrosion. All results obtained by X- ray imaging are valuable information, based on which the approach to conservation treatment can be determined.
Cleaning is the process of removing dirt, debris, corrosion products present on the artifact surface. Cleaning treatments involve mechanical methods using small devices and various tools, and chemical methods using substances to elute the corroded parts. Cleaning is performed under a microscope while observing closely the surface condition during the process. Excessive treatment, beyond what is necessary, is avoided as it may cause damage to the surface. Before using chemicals, the surface condition of the artifact is checked so as to prevent secondary damage.
Stabilization is the process of eliminating factors that cause corrosion or slowing down its progression. It consists of two methods: removal or blocking of chloride salts and anti-corrosive treatments. In the desalination stage, an aqueous alkali solution is used for removing the salt ions, which cause corrosion in ferrous artifacts. Anti-corrosive treatment is performed using corrosion inhibitors on artifacts made of copper alloy.
The deteriorated metal artifact is immersed in a reversible acrylic resin solution and a thin film is formed on the surface so as to act as a barrier to corrosive factors such as oxygen and moisture. There are two methods that may be applied depending on the material and the condition of the artifact: the vacuum impregnation method and the natural impregnation method.