We 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.

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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.