A high sensitivity, low noise and high spatial resolution multi-band infrared reflectography camera for the study of paintings and works on paper

Abstract

Background: Infrared reflectography (IRR) remains an important method to visualize underdrawing and compositional changes in paintings. Older IRR camera systems are being replaced with near-infrared cameras consisting of room temperature infrared detector arrays made out of indium gallium arsenide (InGaAs) that operate over the spectral range of ~900 to 1700 nm. Two camera types are becoming prevalent. The first is staring array infrared cameras having 0.25-1 Megapixels where the camera or painting is moved to acquire tens of individual images that are later mosaicked together to create the infrared reflectogram. The second camera type is scanning back cameras in which a small InGaAs array (linear or area array) is mechanically scanned over a large image formed by the camera lens to create the reflectogram, typically 16 Megapixels. Both systems have advantages and disadvantages. The staring IR array cameras offer more flexible collection formats, provide live images, and allow for the use of spectral bandpass filters that can provide reflectograms with better contrast in some cases. They do require a mechanical system for moving the camera or the artwork and post-capture image mosaicking. Scanning back cameras eliminate or reduce the amount of mosaicking and movement of the camera, however the need to minimize light exposure to the artwork requires short integration times, and thus limits the use of spectral bandpass filters. In general, InGaAs cameras are not sensitive in the 1700 to ~2300 nm spectral region, which has been identified in prior studies as useful for examining paintings with copper green pigments or thick lead white paints. Prior studies using cameras with sensitivity from 1000 to 2500 nm have found in general the performance at wavelengths longer than 1700 nm degraded relative to the performance at shorter wavelengths. Thus, there is interest in a camera system having improved performance out to 2500 nm that can utilize spectral bandpass filters.

Revealing the painterly technique beneath the surface of Vermeer’s Girl with a Pearl Earring using macro- and microscale imaging

“…High resolution multispectral infrared reflectography (MS-IRR) [19,20] was done in order to obtain a more complete visualisation of how the dark underlayers were applied. MS-IRR (50 µm/pixel) was done using two camera systems, the first of which consisted of a Si CCD digital camera and filter that set the spectral sensitivity to 900-1100 nm.…”

“…This greatly improves the transparency of pigments such as lead white, which lack any electronic absorption bands in the visible and infrared (400-2500 nm) [3]. While traditionally infrared reflectography is collected in one broad spectral band, recent research has shown that collecting images in narrower spectral bands can help to isolate different phases of the painting process: for instance, to distinguish a preparatory drawing-often applied with an infrared-absorbing material-from the partially penetrated paint layers [20]. These narrower spectral bands (3-300 nm) also allow for specific pigments to be separated from each other within the paint layers [3].…”

Review of Methods for Documentation, Management, and Sustainability of Cultural Heritage. Case Study: Museum of King Jan III’s Palace at Wilanów

“…Conventional IRR is performed by acquiring the image in wide near infrared band, but recently multispectral sensors collecting several narrower NIR bands are becoming increasingly popular [99]. Since the pigment's layer of a painting absorbs much less infrared radiation compared to visible radiation, the presence of underdrawings may be detected as well as changes in the composition [95,100,101]. Near infrared reflectography has proved its usefulness in pigment identification and distinguishing replicas [102].…”

“…By adding the temporal information to 3D spatial data and database containing descriptive information, it is more and more common to build a temporal GIS (or 4D GIS) allowing one to query and visualize objects belonging to cross-cut different time periods [189]. Depicting archaeological data complexity, 4D GIS has been used in many archaeological applications [100,[190][191][192][193].…”

Spectral information to get beyond color in the analysis of water-soluble varnish degradation

“…Spectral imaging is an emerging tool in analysis in the field of conservation and restoration of Cultural Heritage (CH) [1,2]. Some of the most relevant applications found are the identification of pigments and materials used in the original artworks [3,4], the characterization of the preservation state using spectral ranges beyond the visible [5] and the visualization of hidden layers or "pentimenti" using the infrared range [6]. However, few studies have focused on the use of spectral imaging on the ageing process of the materials commonly used in artworks or ancient texts [7,8].…”