The Noninvasive Analysis of Paint Mixtures on Canvas Using an EPR MOUSE

An Introduction to the Electron Paramagnetic Resonance Spectral Library of Pigments

A library cataloguing the electron paramagnetic resonance (EPR) spectra of artists’ pigments has been created. It contains spectral data collected using several spectrometers that operate at different frequencies for, currently, 51 pigments. The library is intended to serve as an open-access reference database for the scientific studies of cultural heritage objects that utilize this analytical technique. Furthermore, it is a living repository, in that entries will be added as more pigments found to have EPR signals at room temperature are studied. Because EPR is less well established in the field of heritage science than some other common spectroscopies, this companion paper serves as an educational supplement to the library. It focuses on first, describing the theory of EPR to the level necessary to understand the origins of spectral features and to utilize these for pigment identification, and then, on discussing the organization of the library to facilitate the navigation of its contents.

Mapping Pigments in a Painting with Low Frequency Electron Paramagnetic Resonance Spectroscopy

An electron paramagnetic resonance (EPR) mobile universal surface explorer (MOUSE) was recently introduced for noninvasively studying paramagnetic pigments in paintings. This study determined that the EPR MOUSE could map the spatial locations of four pigments in a simple impasto painting. Results from three spectral identification algorithms were examined to assess their ability to identify the pigments using an unsupervised approach. Resulting pigment maps are displayed as colorized images of the spatial distribution of the pigments. All three algorithms produced reasonable representations of the painting. The algorithms achieved excellent true positive, true negative, false positive, and false negative rates of ≥0.95, ≥0.98, ≤0.02, and ≤0.05, respectively, for the identification of the pigments. We conclude that the EPR MOUSE is suitable for accurately mapping the location of paramagnetic pigments in a painting.