The reference compounds belong to the classes of polysaccharide (cellulose 63600; Arabic gum 63300), lipid (carnauba wax 62300; beeswax 62200; shellac wax 60550), proteinaceous (hide glue 63020; bone glue 63000; casein 63200) and natural resinous (sandarac 60100; manila copal 60150; colophony 60310; Venetian turpentine 62010; dammar 60001; mastic 60050; shellac 60480; dragon's blood 37000) materials.
The botanical origin and the chemical composition of the analyzed diterpenoid resins (i.e., colophony, Venetian turpentine, sandarac and Manila copal) are listed in Table 4 .
In particular, an accurate wavenumber correspondence is observed between Venetian turpentine and colophony, on one hand, and between sandarac and Manila copal, on the other, reflecting the respective alike compositions as reported by Daher et al.
The weak symmetric C[H.sub.3] stretching band, with the maximum being placed near 2880 [cm.sup.-1], appears more resolved in Venetian turpentine and colophony with respect to sandarac and Manila copal which present the additional, sharp symmetric C[H.sub.2] stretching band maximum at 2857 [cm.sup.-1].
Moreover, sandarac and Manila copal display an additional weak peak at 4615 which can be attributed to the combination of v(C-O)+ v(C[H.sub.2]) .