Time‐of‐flight secondary ion mass spectrometry imaging in cultural heritage: A focus on old paintings

Abstract

Time-of-flight secondary ion mass spectrometry (TOF-SIMS) imaging is a surface analysis technique that identifies and spatially resolves the chemical composition of a sample with a lateral resolution of less than 1 μm. Depth analyses can also be performed over thicknesses of several microns. In the case of a painting cross section, for example, TOF-SIMS can identify the organic composition, by detecting molecular ions and fragments of binders, as well as the mineral composition of most of the pigments. Importantly, the technique is almost not destructive and is therefore increasingly used in cultural heritage research such as the analysis of painting samples, especially old paintings. In this review, state of the art of TOF-SIMS analysis methods will be described with a particular focus on tuning the instruments for the analysis of painting cross sections and with several examples from the literature showing the added value of this technique when studying cultural heritage samples.cultural heritage, organic matters (oils and proteins), pigments, TOF-SIMS imaging | INTRODUCTIONCertain objects and know-how have cultural significance in our societies; that is, they are inherited from a common past and are meant to be preserved and passed down from generation to generation. These can be works of art such as frescoes, paintings, or jewelry, and also statues, ruins, and everyday objects such as pottery, tools, remedies, and cosmetics. All of which are a testimony to the skills and technical knowledge of the past societies. The expertise and actions of, for example, curators and restorers play an important role in this generational transmission of cultural heritage. Given the variety of questions that can arise regarding objects made of different structures and materials, combining several disciplines appears to be a beneficial approach. A better understanding of the history of material productions from the past can also be done by relying on the physics and chemistry of their constituent materials. Although microscopic information was in the past inaccessible, the craftsmanship knowledge has taken into account the link between specific processing of materials and the aspect and properties of the crafted objects. Today, the possibility to analyze with precision their composition provides insight into the object as it was designed. In the case of old paintings, the chemical identification of organic and inorganic pigments, as well as that of the binders that contain them, provides valuable information about the painter's technique, the nature and origin of the ingredients and their aging, or even their state of degradation. This information can then be combined with the knowledge and expertise of restorers and curators.A painting is made by successively applying layers of various mixtures of pigments in one or more binders, such as oil, egg, or animal glues. These layers are a few microns to a few hundred microns thick.Particles of colored materials dispersed in this way in more or less transparent matrices will create e...

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