Max Ernst was one of the most influential artists associated with both the Dada and Surrealist movements. However, until now, only few scientific studies have been devoted to his works. This paper presents the results of a multi-analytical investigation on six oil paintings, made between 1927 and 1942, belonging to the Peggy Guggenheim Collection in Venice (Solomon R. Guggenheim Foundation, New York). Through a combined art historical and scientific approach, this study aims at understanding Ernst’s painting techniques, including frottage, grattage, dripping, and decalcomania, the used materials, and the state of conservation of the artworks. Non-invasive in situ investigations were performed by means of Vis–NIR multi-spectral imaging, X-ray fluorescence, external reflection FTIR and Raman spectroscopy. Imaging analysis revealed important information about Ernst’s painting methods while the other techniques provided useful information about the ground layer, the painting materials and the presence of alteration products. Ernst’s palette discloses great freedom in his use of materials and evolution during the time. This investigation demonstrates that an integrated, non-invasive, diagnostic approach provides a thorough analysis of materials and execution techniques of Ernst’ masterworks allowing an in-depth knowledge of his highly skilled work.

The study at the Peggy Guggenheim Collection in Venice highlights critical interactions between indoor air quality, visitor dynamics, and microclimatic conditions, offering insights into preventive conservation of modern artworks. By analyzing pollutants such as ammonia, formaldehyde, and organic acids, alongside visitor density and environmental data, the research identified key patterns and risks. Through three seasonal monitoring campaigns, the concentrations of SO₂ (sulphur dioxide), NO (nitric oxide), NO₂ (nitrogen dioxide), NO_x (nitrogen oxides), HONO (nitrous acid), HNO₃ (nitric acid), O₃ (ozone), NH₃ (ammonia), CH₃COOH (acetic acid), HCOOH (formic acid), and HCHO (formaldehyde) were determined using passive samplers, as well as temperature and relative humidity data loggers. In addition, two specific short-term monitoring campaigns focused on NH₃ were performed to evaluate the influence of visitor presence on indoor concentrations of the above compounds and environmental parameters. NH₃ and HCHO concentrations spiked during high visitor occupancy, with NH₃ levels doubling in crowded periods. Short-term NH₃ campaigns confirmed a direct correlation between visitor numbers and the above indoor concentrations, likely due to human emissions (e.g., sweat, breath) and off-gassing from materials. The indoor/outdoor ratios indicated that several pollutants originated from indoor sources, with ammonia and acetic acid showing the highest indoor concentrations. By measuring the number of visitors and microclimate parameters (temperature and humidity) every 3 s, we were able to precisely estimate the causality and the temporal shift between these quantities, both at small time scale (a few minute delay between peaks) and at medium time scale (daily average conditions due to the continuous inflow and outflow of visitors).