A joint use of Raman and infrared spectroscopies for the identification of natural organic media used in ancient varnishes

Abstract Various natural organic film‐making media from several chemical families have been used as varnishes. An improvement in the identification of these materials by a combination of Raman and infrared spectroscopies is presented here. Fourteen unaged reference samples representative of resins, glues, gums and oils were analyzed. FT‐Raman and infrared spectra were all compared in order to discriminate the different classes of organic media by considering their spectroscopic features. It led to a flowchart for material discrimination based on simple, notable and specific criteria. It appears that the different families (gums, glues, oils and resins) and subfamilies (di/triterpenoids resins) are easily differentiated thanks to their specific structural composition. However, differentiating between compounds from a same subgroup, for example diterpenoid resins, could be ambiguous because the spectra depend on the sample aspect, age and degradations. Copyright © 2010 John Wiley & Sons, Ltd.