## 3 Results
As seen from the phasor plot, mean \(g\) and \(s\) values obtained with the imaging mode (g = 0.78 and s = 0.28) differed slightly from the respective values measured with the single-point approach (g = 0.82 and s = 0.29). The main moments characterizing the painting distribution for \(g\) and \(s\) coordinates--namely, variance, skewness, and kurtosis--are also reported in Figure 2d. The difference between the mean \(\tau\)-phases derived from the imaging (2.89 \(\pm\) 0.1 ns) and the single-point (2.44 \(\pm\) 0.1 ns) modes is attributed to the reduced SNR of the imaging mode--caused by a shorter integration time--as well as to the fluctuation of the SNR introduced by the reduced distance stability between the sample and the probe, which is hand-held by the operator during the imaging acquisition. Such error becomes less significant when mapping a specimen composed of materials with very different fluorescence lifetimes (for example, the original and retouched areas of a painting). However, in this study, we chose to consider only point data, so as to provide a more precise characterization of the analyzed materials. Figure 1: Fluorescence emission (**a**) and Raman (**b,c**) spectra of the analyzed materials. The results of the lifetime phasor analysis of the linseed oil, mastic, and beeswax samples are reported in Figure 3. The \(\tau\)-phase values of the three materials derived from the phasor plot are clearly distinguishable, resulting in 2.44 \(\pm\) 0.1 ns, 2.26 \(\pm\) 0.1 ns, and 2.11 \(\pm\) 0.1 ns, respectively. Figure 4a,c show the comparison of the \(\tau\)-phases of the three binding materials mixed in comparable quantities with the red and the black pigments. The fluorescence lifetimes of iron oxide (IO) and lampblack (LB)--3.4 ns and 3.3 ns, respectively--are longer than those of the mixtures. In other words, the presence of the pigment in the binder results in an increase in the \(\tau\)-phase of the pure binder--particularly for beeswax, which increases from 2.1 ns to \(\sim\)3 ns in both the pigment mixtures. An increase in \(\tau\)-phase, albeit less significant, is also observed in the mastic-based mixtures (M + IO and M + BW): the fluorescence lifetime of the pure resin (2.3 ns) becomes 2.6 ns with the addition of OI and 2.5 ns with LB. In contrast, the change in \(\tau\)-phase is negligible for linseed oil, resulting in \(\sim\)2.4 ns in  
Figure 3: Results of the lifetime phasor analysis of LO, M, and BW samples: phasor plot (**a**) and plot of the mean \(\tau\)-phase values (**b**), with corresponding standard deviations indicated by the error bars. Figure 2: Imaging and single-point FL analysis of an LO sample. (**a**) Bright-field image of the sample, i.e., linseed oil spread on a microscope slide (the red dashed square indicates the region where measurements were acquired, while the black dashed rectangle shows the area magnified in (**b**), as seen by the CCD camera of the FL instrument working in imaging mode. (**b**) Detail of the sample showing the fluorescence lifetime map in color-coded scale obtained in imaging mode (color bar corresponding to the \(\tau\)-phase values); the red spot is from the aiming beam. (**c**) The same lifetime map superimposed on the linseed oil sample, illuminated with a low-pressure mercury lamp. (**d**) Phasor diagram showing the distribution of phasors calculated from the imaging and the single-point modes on the same area. both the pure form and in the mixtures with the pigments. This difference in \(\tau\)-phases is consistent with the Raman results of the mixed samples (Figure 4b,d), especially those based on linseed oil as compared to the other mixtures. The characteristic peaks of the oil compete in intensity with those of the pigment, confirming its lower influence on the overall Raman signal. Finally, we show the results of the combined FL-Raman analysis of the mixtures laid on bronze supports (Figure 5). Here, the advantage of integrating data from two complementary techniques is particularly evident.