# Spectral Raman Database of Modern Acrylic Paints at 532 nm and 633 nm Laser Excitation Wavelengths
## 2 Experimental
### Experimental Instrument  
The \(\mu-\)Raman spectroscopic analyses were performed using a Horiba \(-\)Jobin Yvon\(-\)LabRAM \(\mu-\)Raman spectrometer, controlled by Labspec 5 and equipped with two laser sources: a He-Ne laser (633 nm emission wavelength) of 17 mW of power and a Nd:YAG laser (532 nm wavelength) of 50 mW of power. In order to reduce the power of the laser on the samples, when deemed necessary, in the laser ray path have been introduced filters for the attenuation of the laser power with dif-ferent optical densities (OD) which is obtained by the following relationship:  
\[\%\text{Transmission}=\text{T}=10^{-\text{OD}}\cdot 100\% \tag{1}\]  
Thus, when the filter used has an OD = 0.3, then the percentage of the power transmitted is T% = 50%; for OD = 0.6%, then %T = 25%; for OD = 1, then %T = 10%; for OD = 2, then %T = 1%; for OD = 3, then %T = 0.1%; and for OD = 4, then %T = 0.01%. The number of the scans and the acquisition time used to collect the Raman spectra were not the same for all the pigments but were modified on the basis of the analysed pigment in order to maximize the detectability of Raman features shown by the representative Raman spectra. Table 2 summarizes the experimental conditions for the collection of the Raman spectra. Measurements were conducted using athe confocal microscope BX40 (by Olympus, Tokyo, Japan) with a 50\(\times\) objective. Holographic grating of 1800 groves/mm was used during the Raman measurements. The spectral resolution was 1 cm\({}^{-1}\). All Raman spectra presented in this work were baseline-corrected using OriginPro software (OriginPro 2018 (64 bit) SR1 b9.5.1.195).  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Pigment** & **N\({}^{\circ}\) Figure** & **Substrate** & **Laser** & **Optical Filter** & **Acquisition Time (s)** & **Scan** \\ \hline \multirow{6}{*}{**PB**} & \multirow{6}{*}{3} & \multirow{6}{*}{w} & R & D0 & 20 & 10 \\ \cline{3-6}  & & & G & D1 & 10 & 20 \\ \cline{3-6}  & & & R & D0 & 10 & 10 \\ \cline{3-6}  & & & G & D1 & 10 & 10 \\ \hline \multirow{6}{*}{**PBC**} & \multirow{6}{*}{5} & \multirow{6}{*}{w} & R & D0 & 20 & 10 \\ \cline{3-6}  & & & G & D0 & 10 & 10 \\ \cline{3-6}  & & & g & R & D0 & 15 & 20 \\ \cline{3-6}  & & & G & D1 & 10 & 10 \\ \hline \multirow{2}{*}{**IB**} & \multirow{2}{*}{6} & \multirow{2}{*}{w} & R & D0 & 20 & 10 \\ \cline{3-6}  & & & g & R & D0 & 20 & 15 \\ \hline \multirow{6}{*}{**PG**} & \multirow{6}{*}{8} & \multirow{6}{*}{w} & R & D0 & 20 & 10 \\ \cline{3-6}  & & & G & D0 & 20 & 10 \\ \cline{3-6}  & & & g & R & D0 & 10 & 10 \\ \cline{3-6}  & & & G & D1 & 10 & 10 \\ \hline \multirow{2}{*}{**PRM**} & \multirow{2}{*}{10} & \multirow{2}{*}{w} & R & D0 & 20 & 20 \\ \cline{3-6}  & & & g & R & D0 & 5 & 100 \\ \hline \multirow{2}{*}{**LY**} & \multirow{2}{*}{12} & \multirow{2}{*}{w} & G & D06 & 10 & 30 \\ \cline{3-6}  & & & g & G & D1 & 10 & 10 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Experimental conditions for the collection of the representative Raman spectra.  
All pigments were analysed with both the lasers at 532 nm and 633 nm. In the cases where the collected spectra, at each laser, show the same Raman features, only the representative Raman spectrum collected with the better signal to noise ratio will be displayed.