Fig. 5
ATR-FTIR spectra of fresh (A), fossil (B), and sediment-encased matured (C–H) resins. (A) Fresh Aleppo Pine resin from outside of the FSA (Sierra Vista, AZ, USA). Two spectra were obtained from the same sample. (B) Natural Eocene fossil Baltic amber MAI UG 508,762 (also ATR-FTIR and baseline corrected) modified from Szwedo & Stroiński37 (CC BY-NC-SA 4.0). (C) Run A dry P. sylvestris resin (excluding its possible leakage). (D) Run A P. mugo resin. (E) Run B dry P. sylvestris resin. (F–H) Run C contained two samples of each resin type (e.g., two separate pieces of P. mugo resin were compacted separately into two separate clay tablets and then matured at the same time in the maturation chamber, alongside the other Run C samples). (F) Run C dry P. sylvestris resin. (G) Run C sticky P. sylvestris resin. (H) Run C P. mugo resin. Red dots indicate ~ 1700 cm–1 C=O stretching peaks that are not the most intense peak relative to their spectrum, as expected as resins mature. Purple dots indicate ~ 1605 cm−1 peaks that might derive from aromatic C=C stretching, as possibly expected during resin maturation. Negative absorbance values (grey) in (A) and especially (H) indicate difficulties in background correction (e.g., air pockets and reduced contact with resin) and/or suboptimal measurement parameters in OMNIC software; still, many characteristic peaks can be inferred in these spectra.
