Score plot of PC1 and PC2. Variables: 40 fitting parameters of the Raman CH
bands, items: 37 reference samples+20 archeological copals(10 internal and 10
surface sampling). The archeological copals are grouped with the African copals.
Moreover, the internal (IS) and external samplings (SS) are in a same group
demonstrating that ageing is not, to a certain extent, an obstacle to the material
recognition.