ToF-SIMS spectra of historical inorganic pigments: Natural and synthetic ultramarine blues and smalt in both polarities

Time-of-flight secondary ion mass spectrometry (ToF-SIMS) is increasingly used to analyze cultural heritage materials because it can simultaneously detect organic and inorganic materials while mapping them on a surface. The precise identification of a pigment in a specific layer of a painting or of remaining color on a statue can inform about the technique used or the time of manufacture as well as expose possible forgeries when anachronistic ingredients are identified. Reference spectra are required to confidently identify a given pigment using ToF-SIMS. This paper focuses on four blue pigments manufactured following historical recipes: two natural ground and processed lapis lazuli pigments, one synthetic ultramarine pigment, and the blue-colored ground cobalt glass pigment smalt. The positive and negative polarity ToF-SIMS reference spectra using a Bi3+ primary ion species are presented. Differentiating these family of pigments is of interest as they have similar compositions but are used in very different contexts. It is particularly noteworthy that the two natural lapis lazuli pigments can be distinguished from the synthetic counterpart ultramarine using ToF-SIMS.