Fig. 2From: Analysis of red chalk drawings from the workshop of Giovanni Battista Piranesi using fiber optics reflectance spectroscopya FORS spectra (normalized and corrected for multiplicative scattering effects) of dry Frankenalb red chalk applied in high (dark green) or low (light green) intensity on modern paper (gray). b 1st derivative of the spectra between 500 and 650 nm, showing the formation of a shoulder resulting from paper show-throughBack to article page