Fig. 4
![Fig. 4](http://media.springernature.com/full/springer-static/image/art%3A10.1186%2Fs40494-021-00623-z/MediaObjects/40494_2021_623_Fig4_HTML.png)
Identification of pigments in the RF-5 sample. Blue color. a Microphotograph of the cross section under visible light; b Elemental distribution EDX map; c SEM–EDX spectrum from the black box area; d Raman spectrum from the black particle
Identification of pigments in the RF-5 sample. Blue color. a Microphotograph of the cross section under visible light; b Elemental distribution EDX map; c SEM–EDX spectrum from the black box area; d Raman spectrum from the black particle