Fig. 4From: Analysis of red chalk drawings from the workshop of Giovanni Battista Piranesi using fiber optics reflectance spectroscopya–c SEM images (BSE mode) of red chalk applied dry on paper: Frankenalb (a), Theley1 (b) and synthetic (c). The white particles consist mainly of hematite and minor rutile. The gray particles include illite, kaolinite, and quartz (Hm: hematite, Ill: illite, Kln: kaolinite, Qz: quartz, Rt: rutile)Back to article page