Surface-Shape Studies of Gauguin's Monotypes

Starting in the 1890’s the artist Paul Gauguin (1848-1903) created a series of monoprints and drawings using techniques that are not entirely understood. To better understand the artist’s production methods, the analytical imaging technique of quantitative reflectance transformation imaging (Q-RTI) was used to assess the surface shape of a number of these graphic works that are now housed at the Art Institute of Chicago. The RTI method uses multiple images of Gauguin’s graphic works captured from a fixed camera position, lit from various different directions to create an interactive composite image that reveals textural characteristics. These ‘active images’ reveal details on the sequence of inks applied to the surfaces of the prints and blind incisions in the paper substrate that help resolve longstanding art historical questions about the evolution of Gauguin’s printing techniques. Q-RTI is an advancement of the general RTI technique that has become an increasingly popular method with conservators as a practical and repeatable way to digitally capture the surface texture a work of art. Here we will demonstrate how it is possible to quantify RTI’s by using 3-d printed calibration targets with known surface normal characteristics. Additionally, we show how closely traditional RTI capture methods resemble ground truth measurements made by white light interferometry and photogrammetry with the ultimate aim of assigning error bounds to the RTI technique. Lastly plenoptic imaging and other novel imaging tools (such as coherent reflectance imaging) will be described as alternative methods to examine the surface-shape of cultural heritage artifacts with increased fidelity, accuracy, and precision.