# Porcelain Enamel Coatings for Building Facades
## 2 Materials and Methods
### Characterization
The resistance to UV radiation was tested in accordance with the ASTM G154 standard [33], with an irradiation of 0.71 W/m\({}^{2}\) and a temperature of 60 \({}^{\circ}\)C, employing a UV173 Box Co.Fo.Me.Gra (Co.Fo.Me.Gra, Milan, Italy), with a wavelength of 313 nm. Changes in the aesthetic properties were evaluated through gloss and color measurements. The test was conducted on two samples per typology, taking three measurements of gloss and colorper sample. The reported values of gloss and color changes are the average values of the two samples. Another potential damaging factor for coatings is the presence of dust and pollutants in the natural environment. The resistance of enamel coatings to air pollution and soiling was tested following the ASTM D7897 standard [34]. The soiling solution simulating the average conditions of three US cities (Phoenix, Arizona; Miami, Florida; and Youngstown, Ohio) was prepared by mixing equal volumes of (1) a dust suspension (2.3 g/L); (2) a salt solution (1.0 g/L); (3) a particulate organic matter (POM) solution (1.4 g/L); and (4) a soot suspension (0.26 g/L). The dust suspension was prepared with 0.3 g/L of Fe\({}_{2}\)O\({}_{5}\) powder, 1.0 g/L montmorillonite, and 1.0 g/L of bentonite. The salt solution was prepared with 0.3 g/L of NaCl, 0.3 g/L of NaNO\({}_{3}\), and 0.4 g/L of CaSO\({}_{4}\) 2H\({}_{2}\)O. The POM solution was prepared by dissolving 1.4 g of humic acid into 1 L of distilled water, while the soot suspension was obtained by diluting 0.26 g of carbon black (Vulcan XC-72) into 1 L of distilled water [34]. In total, three test cycles were performed, each composed of three phases:  
* Weathering-apparatus exposure before soiling, involving 2 cycles, each one with 8 h of UV-A (UV173 Box Co.Fo.Me.Gra--Co.Fo.Me.Gra, Milan, Italy) and 4 h of condensation at 50 \({}^{\circ}\)C. Then, samples were dried under an infrared heat lamp for 5 min at 150 W (Philips IR150R R125, Philips, Eindhoven, Netherlands). * Soiling, consisting of spraying the samples with the soiling solution and drying under an IR lamp for 5 min. * Weathering-apparatus exposure after soiling involves 2 cycles, each with 8 h of UV-A exposure and 4 h of condensation at 50 \({}^{\circ}\)C. Then, the samples were dried under an IR heat lamp for 5 min. The UV-A lamp (UVA-340) had a wavelength of 340 nm and an irradiance of 0.89 W/(m\({}^{2}\) nm). Changes in aesthetic properties were evaluated through measurements of gloss and color. The ASTM D6578 standard was followed to test the resistance of coated samples to graffiti [35]. A homogenous layer of a solvent-based alkyld spray (Dupli Color, Milano, Italy, red RAL 3000) was applied to the samples, which were then cured at room temperature for 24 h [6,35]. Graffiti was removed with a typical organic solvent such as methyl ethyl ketone (MEK) and xylene, and color and gloss were measured. The resistance of the coatings to abrasion was studied through the PEI test [36], generally known for the evaluation of the abrasion resistance of tiles, and the Taber test, mostly used for paint coatings. According to the UNI EN ISO 10545-7(2000) standard [36], the PEI abrader instrument (Ceramic Instruments, Sassuolo, MO, Italy) was used. An abrasive medium composed of 3 g of F80 alumina powder, steel balls of different dimensions (70 g balls with a diameter of 5 mm, 52.5 g with a diameter of 3 mm, 43.75 g with a diameter of 2 mm, and 8.75 g balls with a diameter of 1 mm), and 20 mL of deionized water were applied to the sample surface, and a circular rotation at 300 rpm was imposed on the samples. In total, 5000 PEI cycles were performed, and the abrasion was evaluated by measuring the mass loss after 100, 250, 500, 1000, 2000, and 5000 cycles. The Taber abrasion test was carried out with a Taber Abraser 5131 (Taber Industries, Tonawanda, NY, USA), according to the ASTM 4060 standard [37]. The test involved the rotation of two abrading wheels (CS17) in the opposite direction compared to the sample rotation, for 5000 cycles, with a 250 g load.