Infrared Reflectography (IRR)

Infrared Reflectography (IRR) is supplementary to XRF measurements and is used within the ink analysis protocol to discriminate between the types of inks such as iron gall, mixed, or carbon inks. Operating in the shortwave infrared (SWIR) region of 900–1700 nm, the IRR system extends over the sensing region of the Multispectral Imaging (MSI) system which is limited to 365–1100 nm. Furthermore, IRR is used to reveal underlying writing and pre-drawings in art made with carbon-based materials. Like MSI, the basic principle of IRR is that different wavelengths of light can reveal more information about an object than either the naked human eye or standard cameras can. As the name suggests, IRR relies on infrared wavelengths. The longer infrared wavelengths are able to penetrate most pigments but are absorbed by carbon-containing materials. This property makes IRR an ideal method for revealing the pre- or under-drawings of paintings that are often done in pencil or graphite.