Fig. 7
![Fig. 7](http://media.springernature.com/full/springer-static/image/art%3A10.1186%2Fs40494-019-0345-z/MediaObjects/40494_2019_345_Fig7_HTML.png)
UV–Vis reflectance and FT-IR spectra collected on real cases in comparison with reference standard samples (a Type 1, b Type 2, c Type 3, d Type 4). Spectra are vertically translated for clarity (P1: palygorskite-based Maya blue containing 1 wt% indigo; P03: palygorskite-based Maya blue containing 0.3 wt% indigo; S03: sepiolite-based Maya blue containing 0.3 wt% indigo)