In situ luminescence spectroscopy with multivariate analysis for the discrimination of black ballpoint pen ink-lines on paper

A novel approach to the non-destructive discrimination of black, ball-point pen ink-lines on paper, has been developed which uses a standard luminescence spectrometer coupled with multivariate statistical analysis. The application of Principal Component Analysis (PCA) to these data-sets, followed by linear regression of the loadings, not only facilitates separation of the ink luminescence from that of the paper, but also allows a direct comparison between two ink lines on documents. This data reduction means that such a comparison can be done on an effectively univariate basis whereby a straightforward statistical comparison is made between two numbers, each characteristic of an ink. Thus the question, in the forensic context, of whether two ink-lines are indistinguishable may be answered with a particular statistical confidence and the method shows significantly better discrimination, for the pens studied, than conventional forensic investigative techniques involving the luminescence imaging of writing using filtered light.