Fig. 5From: Analysis of red chalk drawings from the workshop of Giovanni Battista Piranesi using fiber optics reflectance spectroscopya–c SEM images (BE mode) of smudged red chalk strokes on paper: Frankenalb (a), Theley1 (b), and synthetic (c). The chalk mineral grains are finely dispersed and scattered across the paper surface to various degrees, depending on grain size and shape: (b) finest grains with the least amount of scattering; (c) coarsest grains, largest amount of scattering, with particles accumulating in the valleys between fibersBack to article page