The reproduction of fire-born soot for comparative cleaning tests on heritage objects

This work describes the design of reproducible mock-ups with controlled soot deposition, created to support comparative cleaning tests within the EU Horizon MOXY project. The latter develops atmospheric, plasma-generated, monoatomic oxygen as a cleaning method to remove (amongst others) fire-born soot from heritage objects. A literature review highlights the complexity of soot while revealing a lack of focus on the representativeness of artificial soot in previous studies. We benchmarked two approaches: (I) indirect/cold application of pre-fabricated soot and (II) direct/hot application via ongoing combustion. The results demonstrate that direct combustion yields soot with markedly different physical and chemical characteristics. Chemical analysis (Raman, XRPD, TGA, EGA-MS, XPS) and microscopic imaging (3D optical, SEM) revealed differences in composition, morphology, and deposition behaviour on substrates like paper, silk, paint and plaster. We selected the 'smoke drum' method as the most practical and reproducible approach for mimicking fire-born soot in heritage cleaning research.