2.4.2. Optical Microscopy

Cross-sections and paint swatches on the mock-ups were observed using a Zeiss Axio Imager.M2m upright microscope equipped with four objectives (5x, 10x, 20x and 50x) and a Zeiss Axiocam 512 Color digital camera. Images were captured using the Zeiss Zen 2.6 (blue edition) software. Visible light conditions utilized a halogen lamp and an EPI-polarization filter cube. Ultraviolet (UV) conditions utilized a mercury vapor lamp and a FITC filter cube (excitation BP450-490, beam splitter FT 510 and emission LP515).

### 2.4.3. Fourier Transform Infrared (FTIR) Spectroscopy

FTIR in transmission mode was performed using a Bruker Vertex 70 infrared bench spectrometer coupled to a Bruker Hyperion 3000 infrared microscope. Samples were compressed on to a diamond cell with a stainless-steel roller prior to analysis. Spectra were recorded between 4000 and 600 cm−<sup>1</sup> at 4 cm−<sup>1</sup> spectral resolution and 32 scans per spectrum. The collected spectra were compared to in-house and published databases.

## 2.4.4. Raman Spectroscopy

Two different systems were used during this study. Analysis of the fresh and degraded paint films were conducted using a Bruker Optics Senterra dispersive Raman microscope with an Olympus BX51M microscope. The 633 nm laser was used at 5 mW power with an integration time of either 5 or 10 and 10 co-additions.

Raman measurements of the dark needle-like structures formed in the altered paints were conducted on a Horiba XploRA One confocal Raman microscope with an Olympus LMPLFLN-BD 50x, NA 0.5, long working distance objective and 0.05 mW of 785 nm excitation light. A 1200 blaze grating was used. The detector was a 1024 × 256 scientific CCD that was thermoelectrically cooled to −70 ◦C. Two 90 s acquisitions were averaged together. Horiba's "Denoiser" smoothing algorithm was applied to the data. A polynomial baseline was fit to the data and subtracted. Spectra were compared with in-house and published databases.
