Wall Materials and Manufacturing Techniques for Korean Ancient Mural Paintings (Great Gaya, 6th Century)—Discovery of Shells Used in Wall Plaster and Identification of Their Processing Status

Abstract

This study used morphological analysis to identify the materials used for the wall plaster in the Goa-ri Tomb and elucidate the wall manufacturing techniques by determining the processing conditions for the plaster ingredients through a calcination experiment. A glossy nacreous layer (or folia layer) and an adductor muscle scar were identified on the ventral of the shell. The shell section was confirmed in the form of a lens-like prismatic layer (or chalky layer) inserted between the nacreous layer (or folia layer). The calcinated samples showed clusters of polygonal particles of different sizes. The experiment confirmed a process of particles in plate-type–bedded structures converting into shapeless particles followed by recrystallization. The samples calcinated at 650 °C and 750 °C mostly showed plate-type–bedded structures. According to the results of the study, the plaster used on the Goa-ri Tomb walls was confirmed to be made of oyster shells. The existence of many incompletely calcinated shell particles in the plaster indicates that the calcination temperature was not high enough or the heat was not evenly distributed. The Goa-ri Tomb used weaker and less durable plaster made of incompletely calcinated shells, which seems to have caused the extensive exfoliation of the plaster from the wall surfaces.