Effects of artificial patination procedures on the composition and structure of bronze patinas

This study thoroughly investigates artificial patination procedures to gain a deeper understanding of the effects of application method, reagent typology and concentration on the properties of patinated bronze surfaces. Copper and iron salts were selected as reagents and used to patinate a quaternary bronze alloy by immersion and hot-brushing treatments. The aesthetic, structural and chemical properties of the patinated surfaces were investigated by optical microscopy and field emission scanning electron microscopy coupled with energy dispersion spectroscopy, while the mineralogical composition was extensively studied by Fourier transform infrared spectroscopy in attenuated total reflection mode, complemented by micro-Raman spectroscopy and X-ray diffraction. Results show that the immersion method produces dusty patinas with well-defined crystals, except for the samples treated with iron nitrate, which exhibit an etched microstructure. In contrast, the hot-brushing method led to a compact and smooth patina composed of xenomorphic compounds typical of high temperatures. Additionally, the study demonstrates that by properly varying the patination method, as well as the composition and concentration of the patinating reagents, it is possible to control the appearance, the structure and the composition of the patinated bronze surfaces, obtaining a variety of mock-ups representative of outdoor and artistic bronze patinas typical of modern artworks.