Advanced Spectral Imaging for Noninvasive Microanalysis of Cultural Heritage Materials: Review of Application to Documents in the U.S. Library of Congress

Abstract

Hyperspectral imaging was originally developed for remote sensing and astronomical applications, but adaptations of this technology have been of great benefit to the preservation of cultural heritage. Developments in noninvasive analytical techniques have advanced the preservation of cultural heritage materials by enabling the identification and analysis of a range of materials, utilizing their unique spectral response to nondestructively determine chemical composition, and determining states of deterioration and change due to environmental conditions. When used as a tool for noninvasive characterization of cultural heritage, these spectral imaging systems allow the collection of chemical identification information about materials without sampling, which is a critical factor for cultural heritage materials. The United States Library of Congress has been developing the application of hyperspectral imaging to the preservation and analysis of cultural heritage materials as a powerful noncontact technique. It allows noninvasive characterization of materials, by identifying and characterizing colorants, inks, and substrates with narrow-band illumination to protect the object while also monitoring deterioration or changes due to exhibit and other environmental conditions. Contiguous illumination from the ultraviolet, visible, and infrared spectral regions allows the capture of lost, obscured, and deteriorated information. The resulting image cube allows greater capabilities for mapping and coordinating a range of complementary chemical and spectral analyses. The capabilities of this technique are illustrated by a review of results from analysis of the Waldseemü ller World Map, the L'Enfant plan for Washington, D.C., and the first draft of the U.S. Declaration of Independence.

Use of imaging spectroscopy, fiber optic reflectance spectroscopy, and X-ray fluorescence to map and identify pigments in illuminated manuscripts

“…The former mainly uses the spectral differences of artist's materials to enhance the visualization of specific features by creating false color composites, difference images, or principal component images, to separate for example iron-based from carbon-based ink writing (Mrusek et al, 1995;Havermans et al, 2003;France, 2011). Such spectral imaging can be more accurately referred to as multior hyper-band imaging, especially if X-ray or luminescence images are included.…”

An assessment of multimodal imaging of subsurface text in mummy cartonnage using surrogate papyrus phantoms

“…All images were divided by the flat fields prior to subsequent analysis. Analysis involved examination of an image at a single wavelength, taking the ratio of images at different wavelengths, and more sophisticated methods like principal component analysis (PCA: a linear transformation of the images which provides a new set of images which often emphasise differences between the original images) [18].…”

Comparing the effectiveness of hyperspectral imaging and Raman spectroscopy: a case study on Armenian manuscripts

“…Originally a remote sensing technique [32] it has been developed over the years for astrophysics, military applications, medical imaging, and more recently for the nondestructive investigation of works of cultural heritage [6,[33][34][35]. HSI has been successfully applied to a range of heritage material including The Declaration of Independence [36] where alterations to text were revealed, and Edvard Munch's "The Scream" where the pigments used were characterised and mapped [37].…”