  The influence of ns-laser wavelength to discriminate ancient painting
techniques such as are fresco, casein, animal glue, egg yolk and oil was
investigated in this work. This study was carried out with a single shot laser
on samples covered by a layer made of a mixture of the cinnabar pigment and
different binders. Three wavelengths based on Nd: YAG laser were investigated
(1064, 532 and 266 nm). The plasma is controlled at the same electron
temperature after an adjustment of pulse energy for these three wavelengths on
a fresco sample without organic binder. This approach allows to eliminate the
effects of laser pulse energy and the material laser absorption. Afterwards,
the emission spectra were compared to separate different techniques. The
organic binding media has been separated based on the relative emission
intensity of the present CN or C 2 rovibrational emissions. In order to test
the capability of separating or identifying, the chemometric approach (PCA) was
applied to the different matrix. The different solutions in term of wavelength
range to optimise the identification was investigated. We focused on the
evaluation for the laser wavelength to insure a better separation. The
different capacity was interpreted by differentiating 1 Corresponding author.
E-mail address<EMAIL_ADDRESS>2 the binders by the altered
interaction mechanisms between the laser photon and the binders. Also, the
electron temperature in the plasma was estimated, which provided the evidences
to our findings.
