# Analytical Evaluation of Laser Cleaning Effectiveness in the Context of Contemporary Muralism
## 4 Conclusions  
In this study, we conducted an extensive investigation into the laser cleaning of synthetic sprays on both unaged and artificially aged mock-ups, presenting a specific protocol for assessing the effectiveness and safety of laser cleaning on contemporary murals. Through micro-ATR-FTIR analysis, we confirmed the chemical composition of the painting materials. Different binders such as acrylic, alkyld, and styrene-acrylic, along with specific pigments, were identified, providing a foundational understanding for subsequent cleaning assessments. Figure 8: Pyrograms of unaged AcrB–AcrY after one (**a**) and two cleaning cycles (**b**) with QS laser. \begin{table}
\begin{tabular}{c c c} \hline \hline
**AcrB–AcrY Unaged** & **Cleaning Cycle** & **Pigment Pickup** \\ \hline \hline \multirow{4}{*}{
\begin{tabular}{c} QS laser \\ (zone a) \\ \end{tabular} } & QS laser \\  & (zone a) \\  & one cleaning cycle \\ \hline \hline \end{tabular}
\end{table} 
Table 9: Photo of unaged sample AcrB-AcrY and quartz tissue after cleaning with QS laser. Five empirical evaluation criteria were identified and validated analytically, providing a practical insight into the effectiveness of laser cleaning. This approach, expressed through radar charts, demonstrated the influence of the binder type on the overall cleaning performance. The results are further validated by non-invasive analytical measurements. Colorimetric measurements revealed significant \(\Delta\)E values for samples with styrene-acrylic binders, indicating substantial color changes after cleaning. Micro-ATR-FTIR and Py-GC/MS analyses were employed for a deeper understanding of the cleaning process. In particular, micro-ATR-FTIR provided rapid results aligned with empirical observations, but it exhibits limitations in assessing cleaning effectiveness, particularly in cases where the first paint layer and the unwanted top layer share the same binder and contain poorly infrared-absorbing pigments, which leads to potential false negatives. In contrast, Py-GC/MS analysis demonstrated superior sensitivity and specificity compared to FTIR, making it the preferred choice for validating empirical evaluations. The adoption of a passive sampling method with a quartz fiber filter facilitated precise monitoring of laser cleaning action through Py-GC/MS without the need to extract samples directly from the surface of the mock-ups or artwork. Both Q-Switch and Long Q-Switch laser instruments demonstrated comparable cleaning effects, proving especially effective for restoring vandalized murals, with the sole exception of cases where the base paint is styrene-acrylic. The aging of the paint film does not significantly influence the effectiveness of laser cleaning. However, some extra attention must be paid: while the laser effectively removes unwanted paint, it may also erode the most superficial layer of the underlying paint, revealing a surface diminished in binder content but enriched in pigments and fillers; this potential erosion and loss of cohesion could necessitate additional maintenance measures. Our study contributes with empirical insights and establishes a first framework for evaluating laser cleaning procedures that will be further developed and refined in the future. The interplay between binder types, pigments, and laser parameters is crucial, emphasizing the need for a simple and feasible approach to preserve the aesthetic and structural integrity of murals during restoration efforts. As laser cleaning technology evolves in cultural heritage conservation, the passive sampling system for Py-GC/MS analysis promises to provide detailed information on the ablated material components while preserving the integrity of artworks. Furthermore, it is easily adaptable to different application contexts. Our findings provide valuable considerations for conservators, restorers, and researchers engaged in the preservation of street art and murals.