Short-wave infrared reflectance hyperspectral imaging for painting investigations: A methodological study

Reflectance hyperspectral imaging provides a non-invasive tool for the diagnostics, analysis and documentation of paintings. It supplies high quality digital images with spectral information associated to each pixel of the imaged area. Working in the short-wave infrared range (1000-2500 nm) allows for the investigation of inner layers of paintings, by revealing underdrawings, hidden details, and characterizing artists' materials. The performance of spectral imaging systems is usually established in the laboratory using reference targets to measure the system spatial and spectral resolution. However, when dealing with paintings, using custom built test targets made with materials more representative of the artwork can provide a better understanding of advantages and limitations of the system. This paper looks at the benefits of hyperspectral imaging in the 900-1700 nm region as applied to the study of paintings. A test panel target, made according to early Renaissance Florentine painting techniques was used for assessing the diagnostic capability of the hyperspectral system developed at the "Nello Carrara" Institute of Applied Physics. The paper illustrates how different spatial and spectral resolutions can impact the documentation of underdrawings and identification of artists' materials. Finally, the analysis of a fifteenth-century panel painting by Fra Angelico is presented as case study.