The Forbes Pigment Reference Collection: Characterization Using Scanning Electron Microscopy (SEM) and X-ray fluorescence (XRF)
Background: Documents, such as illuminated manuscripts, illustrations and ink sketches, are made with various media, such as iron gall ink, chalk, graphite, or watercolor paint. Many of these media are made of pigments in a wide range of binders.
Reference collections of known and characterized pigment samples can aid specialists in identifying unknown, unstable, or questioned documents and other works. The Library of Congress holds a collection of pigment samples from Harvard’s Forbes’ Pigment Collection. The Forbes’ Pigment Collection is comprised of over 1000 colorants assembled by the late Edward Waldo Forbes, former Director of the Fogg Art Museum at Harvard University. Although the bulk of the collection resides at Harvard University, nineteen additional laboratories around the world share subsets of the collection, including the Library of Congress. This collection has long been used to provide reference samples to aid in the identification of pigments found in conjunction with collections in libraries, archives and museums.
Specialists study media to better understand the nature of documents and other works. Identifying pigments and other media can enable specialists to authenticate questioned documents or identify documents at risk of deterioration from acidic or other problematic media. Such studies can reduce risks to collections while adding value to the knowledge of a document’s provenance and manufacture. Some media (like iron gall ink or verdigris pigments) are acidic and consequently are at greater risk for deterioration and can even contaminate other collections. Characterizing pigments through their respective optical, chemical and physical properties can help specialists “date” documents, since certain pigments were traditionally used at specific times and places. In addition, specialists can estimate the stability, durability and longevity of documents and media made with unstable pigments that might inherently weaken documents.
Project Description: The purpose of the project is to create an “atlas” of pigments, imaged by a scanning electron microscope (SEM) and matched to their Energy Dispersive X-ray Spectroscopy spectra. This will provide, in conjunction with data from other institutions, a database of known pigment characteristics to aid scholars and preservation specialists in the identification of pigmented media present in the Library’s collections.
Update: Protocols for imaging will be developed using the Library’s new Environmental Scanning Electron Microscope.
Image: Photomicrograph of Cu-rich azurite