## 3 Results and Discussion
### Literature Revision of Materials Applied for Cool Surfaces
#### 3.3.1 Pigments  
According to the publications presented in Table 1, the pigments were evaluated through the 14 most relevant publications that are related to the theme of energy use in buildings. Most of the publications are affiliated with research entities based in India and China. Figure 8: Cluster networks of: (**a**) building-materials; (**b**) cool-materials; (**c**) membranes; and (**d**) coatings. \begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline
**Title of Publ.** & **Authors** & **Journal** & **Year of Publ.** & **Ref.** & **Country of Affiliation** \\ \hline Solar spectral optical properties of pigments—Part I: Model for deriving scattering and absorption coefficients from transmittance and reflectance measurements. Solar spectral optical properties of pigments—Part II: Survey of common colorants. Bismuth titanate as an infrared reflective pigment for cool roof coating. Pigmentary colors from yellow to red in Bi\({}_{2}\)Ce\({}_{2}\)O\({}_{7}\) by rare earth ion substitutions as possible high NIR reflecting pigments. A new member of solar heat-reflective pigments: BaTiO3 and its effect on the cooling properties of ASA (acrylonitrile-styrene-acrylate copolymer). Terbium doped Sr\({}_{2}\)MO\({}_{4}\) [M = Sn and Zrr] yellow pigments with high infrared reflectance for energy saving applications. Pigments based on terbium-doped yttrium cerate with high NIR reflectance for cool roof and surface coating applications. Study of solar heat-reflective pigments in cool roof coatings. Surfactant effect on titanium dioxide photosensitized oxidation of 4-dodecyloxybenzyl alcohol. On a cool coating for roof clay tiles: Development of the prototype and thermal-energy assessment. Effects of added ZnO on the crystallization and solar reflectance of titanium-based glaze. & [PERSON], [PERSON], [PERSON], [PERSON], and [PERSON] \\ Performance of near-infrared reflective tile roofs. Environmental impact of cool roof point: case study of house retrofit in two hot islands. Preparation of phthalocyanine blue/rutile TiO\({}_{2}\) composite pigment with a ball milling method and study on its NIR reflectivity & [PERSON], [PERSON] [PERSON], [PERSON], and [PERSON] [PERSON] \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Most important publications about pigments. Pigments were proven to enhance the NIR reflectance for cool coatings and to maintain a wider range of color choices, which opened the way for an industry of geoengineering and chemical solutions for cool materials [27; 28; 31; 33; 62]. The absorption coefficient and the solar spectral backscattering measured in the range of 300-2500 nm determines whether the pigment should be implemented in a cool coating [27]. According to [PERSON] et al. [28], a pigment with a low absorptance is considered cool, whereas a pigment with high NIR transmittance will necessitate an NIR-reflective background (usually white or metallic) in order to form an NIR-reflecting coating. The developed reflective pigments allowed for the transition from lighter colors to dark coating materials, often without compromising the reflective performance. Five dark-colored pigments were analyzed in a study to develop new species of high-NIR reflectance. With a formulation of a 25% weight content of rutile-type titanium dioxide, the white ceramic microspheres, with a 13% weight content, and the heavy calcium carbonate, with a 10% weight content, obtained positive results, and the back temperatures were lowered by 10-20 \({}^{\circ}\)C, compared to normal coatings [62]. In general, the pigments integrated into the matrix of cool materials range from organic, of which most are considered transparent, to complex inorganic color mixed-metal oxides that are often opaque [27; 28]. Cool pigments achieve a high solar reflectance of up to 95%, compared to TiO\({}_{2}\), such as bismuth titanate [29; 30], barium titanate [31], and terbium-doped yttrium cerate [32; 33].