# Analytical Evaluation of Laser Cleaning Effectiveness in the Context of Contemporary Muralism
## 2 Materials and Methods  
### Materials  
#### 2.1.1 Sample Preparation  
The mock-ups were prepared by applying a layer of spray or brush paint on cement mortar, as often found in murals and street artworks. Subsequently, a second layer of paint was applied by spray to simulate an act of vandalism (Figure 1a). The mortar specimens were prepared following this recipe: 2.5 parts (in volume) of mixed sand, composed of 2 parts of natural fine sand (Sabbia AXTON fine naturale di fiume) and 1 part of coarse sand (Sabbia AXTON vagliata); 1 part of cement (i.work TECNOCEM A-LL 32,5 R); and 0.65 to 1 parts of water. The cement used was Portland limestone cement type II, known for its high early strength. It meets the requirements specified in EN standard 197-1 and contains 80-94% clinker excluding calcium sulfate and additives, with the remaining fraction consisting of limestone (TOC \(\leq\) 0.20%, mass (LL)) and possibly other minor constituents. Variations in water volume occurred due to the varying humidity of the sand and environmental conditions. During the preparation process, we adjusted the water content to achieve a consistent mortar consistency. Silicone molds were used to ensure uniform  
Figure 1: (**a**) Stratigraphy of mock-ups; (**b**) three cleaning sections of each sample. size and shape (5 \(\times\) 5 \(\times\) 2 cm). After preparation, the cement samples were air-dried for approximately one month and then polished with 180-grit sandpaper to remove the shiny effect from the front surface and even out the backside. For the painting materials used in this study, three types of spray products were selected, each characterized by a specific binder: an alkyld resin for Montana 94, an acrylic resin for Flame Orange and for the fluorescent colors, Urban Fine-Art Neon, and a styrene-acrylic resin for Alpha Acrilmat. Products containing secondary binders were excluded in order to better correlate the action of the laser to the type of binder. Additionally, a styrene-acrylic water-based paint by Sikkens was chosen as representative of the paints applied by brush or roller. Table 1 provides a complete list of the products used for preparing the reference models. In total, 26 mock-ups were prepared, consisting of two sets of 13 samples. One set of specimens was used as it was, after at least one month of preparation. The second set was artificially aged for 1500 h under artificial solar light. According to the spray producer, the paint required a total drying time of 2-72 h. For the 13 unaged samples, to ensure consistent results, the second paint layer was applied at least 72 h after the application of the first layer. The cleaning procedure was conducted 72 h after the application of the second layer. For the aged sample set, after applying the bottom layer, the samples were aged for 1500 h in a Q-Sun Xe-1 Xenon Test Chamber (Q-Lab Corporation, Westlake, OH, USA) at a constant temperature of 50 \({}^{\circ}\)C. The irradiance was set at 0.68 W/m\({}^{2}\) at 340 nm, using the Daylight Q filter with a cut-on at 295 nm, simulating exposure to direct sunlight. Following the aging process, a second paint layer was applied, and cleaning was performed after 72 h.  
The nomenclature of the mock-ups is based on their binder type, color, and stratigraphy, as listed in Table 2. Based on the authors' observation of the materials most used in murals and graffiti vandalism in Italy, the brush-applied yellow paint (StyY) was only used for the bottom layer, while the fluorescent blue paint (AcrFB) was only applied for the top layer.