For this study we used two Raman spectrometers: A FORAM 685 from Foster & Freeman Ltd. and a LabRam Infinity from Dilor GmbH. The FORAM 685 offers one excitation wavelength at 685 nm. The spectral range is between 400 and 2000 cm–1 with a resolution of 8 cm–1 . The laser power on the samples was about 1.5 mW. The LabRam Infinity offers several laser sources, from which we used 514, 633 and 785 nm. The spectral range we used is between 60 and 3000 cm–1 with a resolution of 4 cm–1. The laser power on the samples can be tuned from 0 to 6 mW. We examined ink lines drawn on white office paper of 26 blue and 26 black ball point pen inks and 63 blue, 60 black, 36 green and 48 red fluid
inks. The inks were examined directly without any sample preparation and after subsequently treating the samples with a solution of poly-L-lysine and a silver colloid to obtain SERRS spectra (SERRS 1). In some cases additional application of an ascorbic acid solution (SERRS 2) leads to better results.