Reflectance Transformation Imaging (RTI) for Documenting Changes through Treatment of Joseon Dynasty Coins

In this paper we present RTI as a documentation tool for visualizing and recording the treatment of coins. RTI, a computational photograph technique based on raking light images, allows interactive re-lighting for vision. Virtual light enhances surface details to examine morphological difference. Stages of conservation treatment were recorded to enhance characteristic features of the relief upon the coin surface and detect and identify weathered characters. Patina removal and consolidation were documented along with the original state. A significant difference in normal and surface texture was observed using RTI viewer and filters. Specular enhancement and normal visualization results were effective for detecting the change of morphology and reflectivity. Characters submersed by thick patina were revealed in Coin 3. Two hidden characters were detected as ‘元’ and ‘訓’. Another illegible character which was previously not regarded as an inscription was discovered. Also, verification of each treatment stage was done to examine whether any foreign material was sufficiently removed. These documentation images indicate that RTI is a promising tool to support manual recording and furthermore allow detection of areas difficult to visualize through the human eye.