Concerning the IR analyses, the spectra decomposition also led
to 10 bands. The PCA results on the reference corpus are presented
on supplementary Figs.s 1s and 2s. The different chemical families
are separated but with less accuracy than for Raman. However, the
IR results can be considered as complementary or validating data,
as they can ensure the classification proposed by the Raman
results or be the key issue in the discrimination of some families.
Indeed, some materials are quite close on the Raman score plots
but well separated on the IR ones, as for example the glues and
frankincenses, or the mastics and shellacs (supplementary Fig. 2s).