Fig. 3From: Rapid identification of cellulose nitrate and cellulose acetate film in historic photograph collectionsTR infrared spectrum of cellulose acetate (a) original data (b) resulting spectrum after application of the Kramers-Kronig transformation (KKT), which is used to calculate the absorbance spectrum. Red solid circles mark the Reststrahlen band which results from a change in the refractive index with strongly absorbing bands, red dashed circle marks the interference fringesBack to article page