Time-of-Flight Secondary Ion Mass Spectrometry, or ToF-SIMS, is an analytical technique that detects and identifies organic and inorganic ions on a solid surface. Because of its micrometric imaging capabilities, ToF-SIMS is increasingly used to analyze cultural objects such as paintings and sculptures to determine their dates and expose possible forgeries. However, ToF-SIMS requires an extensive library of reference spectra for correct identification.

Bouvier et al. compared the spectra of eight lead-based pigments commonly used in painting techniques until the late 19th century. The chosen pigments contained diverse metallic oxides, hydroxides, carbonates, and hydrocarbons found in a representative painting’s cross-section. The specimens analyzed are historically relevant and include pigments such as lead stannate, used in oil painting from the Middle Ages through the 18th century, and lead antimonate, used in Renaissance palettes.

“There is a need to improve the accessibility of the results obtained with ToF-SIMS to reach a broader scientific audience working on cultural objects,” said Caroline Bouvier. “This paper represents a unique set of ToF-SIMS data for pure lead-based pigments, allowing their recognition while comparing their ion signals.”

Specialized manufacturers reproduced historical recipes to prepare finely ground powders for the ToF-SIMS analysis. The calibration list allowed for a complete coverage of the mass range of interest. The major peaks for positive polarity were determined for each of the eight pigments, resulting in unique identifiers.

“This work has the potential to lead to the ToF-SIMS identification of more specific pigments and their degradations,” said Bouvier.

Source: “ToF-SIMS spectra of historical inorganic pigments: Lead-based pigments in positive polarity,” by Caroline Bouvier, Sebastiaan Van Nuffel, and Alain Brunelle, Surface Science Spectra (2024). This article can be accessed at https://doi.org/10.1116/6.0003507.