The use of ultraviolet and visible diffuse reflectance spectrophotometry as a preliminary technique in the investigation of illuminated manuscripts is discussed. Because ancient manuscripts are amongst the most fragile and precious artworks, characterisation of the materials used in their decoration should be performed using non-invasive analytical methods. Ultraviolet and visible reflectance spectrophotometry with optical fibres (FORS) allows non-invasive identification of several colourants used by ancient illuminators, causing no damage or mechanical stress to the artworks subjected to analysis. Identification is usually based on the comparison of analytical data with a spectral database built from painted areas on parchment, created by preparing paints according to ancient recipes as described in medieval technical treatises. Such database and the spectral features of the colourants analysed are discussed, along with the benefits of extending the spectral range of analysis into the shortwave infrared (to 2500 nm). FORS can be best appreciated as a rapid preliminary tool that offers an overview on the main colourants employed and guides the selection of painted areas of manuscripts on which more selective techniques, such as X-ray fluorescence or Raman spectroscopy, can be employed for a more complete and accurate identification.

In situ chemical imaging techniques are being developed to provide information on the spatial distribution of artists' pigments used in polychrome works of art such as paintings. The new methods include reflectance imaging spectroscopy and X-ray fluorescence mapping. Results from these new methods have extended the knowledge obtained from site-specific chemical analyses widely in use. While these mapping methods have aided in determining the distribution of pigments, there is a growing interest to develop methods capable of identifying and mapping organic paint binders as well. Near infrared (NIR) reflectance spectroscopy has been extensively used in the remote sensing field as well as in the chemical industry to detect organic compounds. NIR spectroscopy provides a rapid method to assay organics by utilizing vibrational overtones and combination bands of fundamental absorptions that occur in the mid-IR. Here we explore the utility of NIR reflectance imaging spectroscopy to map organic binders in situ by examining a series of panel paintings known to have been painted using distemper (animal skin glue) and tempera (egg yolk) binders as determined by amino acid analysis of samples taken from multiple sites on the panels. In this report we demonstrate the success in identifying and mapping these binders by NIR reflectance imaging spectroscopy in situ. Three of the four panel paintings from Cosimo Tura's The Annunciation with Saint Francis and Saint Louis of Toulouse (ca. 1475) are imaged using a highly sensitive, line-scanning hyperspectral imaging camera. The results show an animal skin glue binder was used for the blue skies and blue robe of the Virgin Mary, and egg yolk tempera was used for the red robes and brown landscape. The mapping results show evidence for the use of both egg yolk and animal skin glue in the faces of the figures. The strongest absorption associated with lipidic egg yolk features visually correlates with areas that appear to have white highlights. The results are in agreement with prior site-specific amino acid analysis, underscoring the synergy of both methods. The work here demonstrates that NIR reflectance imaging spectroscopy is a useful technique that can identify and map paint binding media based on differences in chemical composition.