Fig. 7
a Normal light photograph of plate 18 (improved positive), with indication of sampling site. b Raman spectrum acquired from sample S1, i.e. a scraping of blue paint from the snowbanks, where two broad bands around 1330 and 1595 cm−1 indicate the presence of a carbon-based black. c BSE image of a portion of sample S1. d EDS spectrum collected from a particle in sample S1, in which the relatively high content of calcium (Ca) and phosphorus (P) enabled to further specify the identity of the carbon-based black pigment as bone or ivory black