Near-infrared imaging helps to investigate the presence and appearance of underdrawing, pentimenti and retouched or heterogeneous areas. It can also provide partial identification and mapping of many pigments. You can view near-infrared images of many of the manuscript folios displayed on this website by selecting the Infrared 'Layer' in the individual folio page.
In March 2014 we began using a 5-megapixel Spectrocam (Pixelteq) equipped with 8 filters covering the spectral range from 350 nm to 950 nm. The system allows us to take multiple images of the same object at different wavelengths. If calibrated to reflectance values, these images can be combined in a multi-spectral image cube. For the purpose of infra-red imaging, we used either an 800 nm long-pass or a 925 nm band-pass filter with 50 nm FWHM. Illumination was provided by one or two lamps fitted with low voltage 35W SoLux bulbs (colour temperature 4700K, beam-spread 36°). Exposure times were adjusted for each filter individually and ranged from 100 milliseconds to 2 seconds.
The near-infrared images were 'registered' (i.e. aligned) with the digital photographs of the corresponding pages using software developed by Dr Damon Conover and provided by the National Gallery of Art and George Washington University in Washington, DC (Conover et al., Applied Physics A 119: 1567, 2015).