3.2.3. Red to Violet Colors

The last important characteristic of the painted enameled porcelains analyzed was the presence of different methods for obtaining red-related colors. The use of hematite or gold nanoparticles was identified in the painted enamels to obtain red, orange to pink/purple hues (Table 2). In only two artifacts, the TH457 bottle (Figures 3 and 7A, white-pink and red) and R1175 plates (Figures 2 and 8A(c,d), orange and red; and Figure 8B(c), red), the use of both methods was observed. Hematite has a well-defined Raman signature, with a strong (ca. 1305–1310 cm−<sup>1</sup> ) mode (resonance signal of magnon mode under green laser excitation) and narrow peaks between 200 and 600 cm−<sup>1</sup> [62,63] (see e.g., Figure 6D(b,b',b"), Figure 7A, Figure 8A(c),B(c) and Figure 12C(b,b')). The magnon mode is very sensitive to the particle size of hematite [63] and the oxygen stoichiometry [62], with small particles giving an orange-red color [29]. Broadening of hematite peaks indicates a partial substitution of iron with other elements, possibly Ti and Al coming from the iron sources [29].

A specific Raman feature referred to the use of gold nanoparticles dispersed in the glassy matrix of the enamel (this type of enamel is at the origin of the label "*Famille rose*" [15,19], with a characteristic broad fluorescence background peaking at ~500–600 cm−<sup>1</sup> under a green laser, corresponding to ~500 nm on the absolute scale [14,18]; see Figure 6C(c) (R1041), Figure 7A (TH457), Figure 8A(d) (R1175), Figure 9B(c) (SN284), Figure 10A(a,a'),B(d) (TH487), Figure 12C(a) (F1429C) and Figure 13C(a) (F1341C)). This method was first experimented with in 17th-century France by the glassmaker Bernard Perrot and then some years later by Johann Kunckel in Germany and certainly by others in Italy before [16,18,64–67]. The presence of gold was also confirmed by pXRF analysis (see arrow on Figure 15—pink, in which the small Au L<sup>α</sup> peak is obvious), with a hardly visible peak well-identified by data fitting. In addition, it is important to note that a very small band characteristic of the As–O stretching band at ca. 820 cm−<sup>1</sup> could be detected along with the fluorescence background characteristic of the use of colloidal gold (seen clearly in Figure 10A(a,a') (TH487) and less intensely in Figure 9B(c) (SN284) and Figure 13C(a) (F1341C)). This band corresponds to the use of Perrot's preparation route for obtaining the colloidal gold precipitate using an arsenic salt, which is different from that of Kunckel, who made use of a tin salt instead [16]. Similar Raman signatures were observed for painted Chinese enameled wares of the same period [14] as well as on French enameled watches [18].
