강진 월남사지 출토 금동풍탁 제작에 적용된 주조와 도금방법 연구

Abstract

The gilded bronze wind-chime, inscribed with Sanskrit characters on each of four faces and plated with gold on the outside, is among the largest wind-chimes excavated so far. This large and golden gilded bronze wind-chime is an artifact attesting to the scale and stature of Wolnamsa temple at its height. The gilded bronze wind-chime, having such important significance, was analyzed using scientific methods to investigate the casting and plating methods applied in its production. The windchime was produced by pouring a bronze alloy in liquid state into a mold and cooling the metal at a relatively slow rate. No high-temperature forging or quenching was performed. A section of the top plate that was repaired exhibits differences in composition from the rest of the body, indicating that the materials used for the top plate and the body were not the same. That is, the material used in the top plate is a material used for repairs after casting the body. The gilded bronze wind-chime contains upwards of 10wt% tin. In order to inscribe Sanskrit on the wind-chime, which measures some 23㎝ high, along with fine fretwork along the edges, a bronze alloy with a low melting point and superior castability was required. To this end, an alloy containing ‘copper-tin-lead’ as its main component as used. However, tin and lead lowered the binding force between the base metal and gold plating layer, and it appears that the current exfoliation of most of the plating layer owes to the high content of tin and lead. Plating was carried out using very thin and uniform gold leaf around 1㎛ in thickness. As for the plating method, the gold leaf plating wherein golf leaf is applied to the surface was used. The gold was analyzed to be approximately 97wt% pure, and no mercury (Hg) was detected. As no mercury (Hg) was detected in the gold plating layer, it could not be ascertained as to whether a substance was used to bind the plating layer to the base metal. However, high carbon content was detected in the dark gray layer left on the surfaces where the plating layer had pealed off, indicating the possibility of lacquer gilding. The characters ‘盖天’ engraved into the surface were created with the hairline engraving technique in which a sharp, triangular-shaped chisel head is used to engrave thin, straight lines. The iron rod used with the chime to produce sound was shaped using pure iron with low carbon content, and was not subjected to additional heat treatment such as carburizing or quenching to increase the strength of the material.