Fig. 3

Irises. a Flower, normal Raman spectra: eosin lake pigment, acquired in the red layers visible in the cross-section shown in Fig. 2a (1); eosin lake reference sample, F.H. Jennison, plate III-1, 1900 [27] (the asterisk indicates a peak due to the barite substrate) (2); and spectrum acquired in the particles that fluoresce bright yellow under UV illumination in the same sample (3). λ₀ = 785 nm. b Pink background, SERS spectra: microsample removed from the pink background (1), and eosin lake reference sample (2). λ₀ = 488 nm