Principal components analysis of the NIR spectra of modern parchment samples. (a) A scatter plot of the eigenvalues of basis function 1 versus basis function 2 for the modern samples. (b) First derivative of the Log(1/R) spectra of modern parchment samples. The more intense peak shown at 1900 nm indicates a steeper slope leading to the water peak at 1947 nm in the Log(1/R) spectra. Modern control (A), Modern scanned 2.16 hrs (B), Modern scanned 2.36 hrs (C) and Modern scanned 12 hrs (D).