Another challenge was to determine if the materiel alteration
has any impact on its recognition. The archeological copals are, in
this case also, good testing samples since their surface presents
more or less alteration. On the PCA score plot (Fig. 6) we can notice
that the surface samples are in the same cluster than the internal
samples, as for the IR results (supplementary Fig. 3s). Moreover,
other transformed materials, for example linseed and poppyseed
oil films, are as well in the oils cluster with a PC1 of 6 and a PC2
around 2 (Fig. 6). Ageing or alteration does not seem, to a certain
extent, hinder the material identification.