Understanding how to safely and effectively remove soot from cultural heritage objects is a pressing challenge—particularly in the aftermath of fires, where artworks, archives, and historic interiors may be exposed to layers of complex, highly variable residues. Within the EU Horizon MOXY project, researchers are developing an innovative cleaning method based on atmospheric, plasma-generated monoatomic oxygen. To support this work, our team at CNR-INO and project partners set out to answer a fundamental question: how can we create realistic, reproducible soot deposits for comparative cleaning tests?

Why reproducing soot matters

Although many studies have investigated soot, the literature shows a surprising gap: artificial soot used in experiments often fails to capture the true complexity of fire-born deposits. Real soot varies widely in composition, particle size, morphology, and how it adheres to diverse heritage materials. Without representative mock-ups, it becomes difficult to reliably test and compare cleaning techniques.

To address this, the researchers designed and benchmarked two controlled soot-deposition approaches:

1. Indirect (“cold”) application of pre-fabricated soot particles.
2. Direct (“hot”) deposition during ongoing combustion.

Both strategies were applied to substrates commonly found in heritage collections—paper, silk, painted surfaces, and plaster—allowing us to evaluate how soot behaves across materials.

Using a comprehensive suite of chemical and microscopic techniques—Raman spectroscopy, XRPD, TGA, EGA-MS, XPS, and 3D optical and SEM imaging—the researchers compared the resulting deposits. The findings were clear:

• Direct combustion produces soot with distinct physical and chemical properties, far closer to what is observed after real fires.
• Differences emerged in composition, particle morphology, and deposition behaviour, all crucial factors for understanding cleaning performance.

Among the tested options, the “smoke drum” method, which relies on controlled direct combustion, proved to be the most practical, reproducible, and representative of fire-born soot. This approach now provides a robust foundation for evaluating the MOXY cleaning technology and for broader heritage science research on soot removal.

By creating realistic mock-ups, the MOXY project strengthens the scientific basis for developing safe, selective cleaning strategies. These results not only support plasma-based methods but also open new possibilities for comparing current and emerging techniques used by conservators worldwide.

Read the full Nature article: https://www.nature.com/articles/s40494-025-02067-1
Read an Author correction here: https://www.nature.com/articles/s40494-025-02224-6