Raman spectroscopy of blue gel pen inks. 
Raman spectroscopy is becoming a tool of major importance in forensic science.  It is a non-invasive, non-destructive analytical method allowing samples to be examined without any preparation.  This paper demonstrates the use of the technique as a general tool for gel pen inks analysis.  For this purpose, 55 blue gel pen inks, of different brands and models representative of gel pen available on the world market at the time of this study, were collected.  A preliminary solubility test in methanol allowed separating them into two classes: 19 dye-based and 36 pigment-based gel inks.  The latter were analysed by Raman spectroscopy (RS) using two wavelength laser sources (514.5 and 830 nm).  Two main pigments were identified, pigment blue 15 and pigment violet 23.