Watching Chemistry Across Ages via Synchrotron Radiation X-ray Microimaging Techniques

Conspectus While this special issue highlights various developments and applications of ultrafast imaging techniques, our focus here is on significantly longer time scales. Instead of examining dynamic systems at submillisecond resolutions, we explore how imaging methods can be utilized to analyze materials that are static at the time scale of data collection to trace reactions that occurred years, decades, or even centuries ago. Some ongoing reactions were quenched at the time of object creation and provide insights into the manufacturing processes used by past civilizations. Others have developed beyond the initial creation of the object, either through deliberate techniques, such as prolonged drying processes in paintings, or via incidental factors that may ultimately cause degradation. It is generally assumed that a rapid chemical reaction indicates artists’ intentions, while reactions occurring over months or years are typically viewed as alterations rather than intentional processes. Therefore, the rate of chemical reactions and their chronology is a crucial factor for scholars for distinguishing between original and nonoriginal materials. When analyzing fragments from cultural heritage objects, it is essential to assess not only the chemical nature of constituents but also their spatial distribution. This information can provide valuable insights into the physical and chemical processes involved in their formation (dissolution, diffusion, precipitation, reduction/oxidation...), as well as their potential origin. Synchrotron radiation (SR)-based micro-X-ray techniques offer both the chemical sensitivity and lateral resolution necessary for these applications. Below, we present three representative examples of study of chemical processes in heritage science. The first case demonstrates how a fragment from an artwork or a craft object can offer insights into the technical and artistic practices developed centuries ago. This is illustrated through studies that elucidate the physicochemical phenomena involved in the production of ancient ceramic glazes from various archeological contexts, such as brown glazes from Song China (10−12th-century) and luster glazes from the Abbasid Caliphate (8−13th-century). The second case examines the reactions involved in degradation phenomena, highlighting that certain heritage materials can be dynamic over periods of months or years. This example also emphasizes the importance of preparing and analyzing mock-up samples to study their evolution under natural and artificial aging conditions. This case is demonstrated with several examples of pigment degradation in paintings, with a focus on the emerald green used by James Ensor (1860–1949) and Robert Delaunay (1885–1941). Finally, the last case shows that, in some cases, attributing the origin of a chemical compound to a material intentionally used by the artist or to degradation phenomena is not straightforward. This is illustrated by the analysis of the origin of different unusual lead compounds detected in Leonardo da Vinci’s (1452−1519) and Rembrandt van Rijn’s (1606−1669) oil paintings.