Infrared spectroscopy for document dating - Advantages, challenges and limitations

Infrared spectroscopy has been increasingly employed for document dating in forensics. In this paper, we evaluate the advantages and disadvantages of methodologies based on this technique, by studying and comparing the artificial and natural aging of paper. Chemometric techniques were used to extract the relevant information. Principal component analysis (PCA) enabled observation of changes in the paper spectral profiles over time, indicating the influence of different storage conditions (temperature and exposure to UV radiation) on the aging process. This made it possible to observe what different storage conditions resulted in different degradation processes. Regression models based on partial least squares (PLS) were used to select variables such as the genetic algorithm (GA) and the generalized least squares weighting (GLSW) filter. The model that best described the dataset was the one using GLSW for both naturally and artificial aging, with α equal to 0.032 for artificial aging and α equal to 0.112 for natural aging. In this paper we evaluate the complexity of infrared spectroscopy and chemometric approaches, showing that since the degradation of paper depends on several factors, these methodologies must be carefully evaluated before being used for forensic purposes.