Evaluation of hydrophilicity and moisture adsorption characteristics of inorganic mineral pigments to sustain ancient paintings

Abstract

Objectives: Inorganic mineral pigments were widely used in ancient painted artworks, and their adsorption characteristic of water vapor in the environment is one of the reasons affecting the deterioration process of paintings under environmental humidity. This paper investigates the characteristics and mechanism of the water vapor adsorption process of inorganic mineral pigments in order to guide the conservation of ancient painting artworks. Material and methods: The contact angle and isothermal hygroscopic curves of common inorganic mineral pigments were measured, as well as the nanoscale pore characteristics of mineral pigments and the effect of gelatin on the hygroscopic process of mineral pigments. The hydrophilic and hygroscopic properties of different mineral pigments were analyzed and compared. Results: Earthen red and Kaolinite have been the strongest hygroscopic minerals, and their adsorption processes include adsorption on the particle surface and also capillary condensation. The hygroscopicity of mineral pigments containing iron oxide and carbonate was moderate, with moisture adsorption occurring mainly on the particle surface, whereas the other mineral pigments had little hygroscopicity. Furthermore, the gelatin used to mix mineral pigments has the ability to invade the nanoscale pores of the pigments and modify the pigments' water vapor adsorption process. Conclusion: The results of the study can provide a theoretical basis for revealing the deterioration process of ancient painting artworks under the influence of the climatic environment, and can be useful in proposing conservation measures for painted artworks.

Keywords

• Environmental humidity
• Mineral pigment
• Vapor adsorption
• Contact angle
• Isothermal hygroscopic curve
• Nitrogen adsorption method