Application of the laser spectroscopy techniques for analysis of pigments on paper

2005 
Techniques of laser emission spectroscopy such as LIPS and LIF are applied to identify pastels and pigments composition for the use in conservation of historical documents. The question of data reliable for pigment identification by these techniques is considered. For model samples made of the cotton paper of chemical composition corresponding to the historical ones, and coated with pastels of different colors the LIPS and LIF spectra are recorded. Samples are excited by the pulsed Nd:YAG laser operating at 355 or 266 nm. The reference Raman spectra are collected, too. Bands characteristic for the blue pigments: PB15, PB29; violet one PV16, and yellow PY 184 are identified exclusively by LIPS in agreement with literature. Also additives such as the barium white found in the Scarlet pastel, and ultramarine (Na 8-10 [Al 6 Si 6 O 24 ]S 2-4 ) with titanium white (TiO 2 ) in the Phthalo Blue are identified, and confirmed by the Raman technique as well. The pigments anthraquinone (PR 168), isoindolinone (PY 110) and monoazo (PY 74) are not revealed. In the LIF spectra only a broad band centered at 612 nm and corresponding to anthraquinone (red pastel) can be clearly assigned.
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