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

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 (C) 2010 John Wiley & Sons, Ltd.