Fig. 3

Photo image (a), typical Raman spectra (b), and Raman intensity images (c–k) collected from the paint branches distributed on a glass surface. The area in a of 30 μm × 30 μm was scanned. Raman spectra were collected under an objective lens of 40×, integration time of 1 s for each pixel of 1 μm × 1 μm (to create a matrix of 30 × 30). b Shows the Raman spectrum of ABS to compare with 3 typical spectra collected from the marked positions in a, and the averaged spectrum of 900 spectra (30 × 30), with intensity off-setting for presentation. The intensity images (c–k) are mapped at a blank wavenumber window (c), two broad peaks (suspected colourant) (d, e), the characterised peaks of acrylic (f–j), and their merged one (using logic-OR) (k), as marked under each image (and the peak width) and in b, after 20% colour off-setting