Reflectance transformation imaging for documenting changes through treatment of Joseon dynasty coins

Abstract

AbstractWe present reflectance transformation imaging (RTI) as a documentation tool for visualizing and recording the treatment of coins. RTI—a computational photograph technique that calculates light positions—allows interactive relighting for vision. Virtual light enhances surface details for examining morphological difference. By applying Dome RTI method, stages of conservation treatment were recorded to enhance the overall characteristic features of the relief upon the coin surface, and then detect and identify weathered characters. Patina removal and consolidation were documented along with the original state; a significant difference in the coin’s surface was observed using different filters of the RTI viewer. Specular enhancement and normal visualization results were most effective for detecting the change in morphology and reflectivity. Microscopic RTI was applied to visualized minimal changes of characters between treatment stages. Character “常” of coin 1 showed changes in the cleaning of dirt and removal of alumina powder. The character “元” of coin 3, originally covered by a thick patina, revealed clear strokes using virtual relighting through RTI. These documentation images indicate that RTI is a promising tool to support manual recording of conservation stages and, furthermore, allow detection of areas difficult to visualize through the human eye.