Holy Smoke in Medieval Funerary Rites: Chemical Fingerprints of Frankincense in Southern Belgian Incense Burners Jan Baeten 1,2 , Koen Deforce 3 , Sophie Challe 4 , Dirk De Vos 1,2 *, Patrick Degryse 2 1 Center for Surface Chemistry and Catalysis, KU Leuven, Leuven, Belgium, 2 Centre for Archaeological Sciences, KU Leuven, Leuven, Belgium, 3 OD Earth and History of Life, Royal Belgian Institute of Natural Sciences, Brussels, Belgium, 4 Service public de Wallonie, Direction de l’Arche ´ ologie, Jambes, Belgium Abstract Frankincense, the oleogum resin from Boswellia sp., has been an early luxury good in both Western and Eastern societies and is particularly used in Christian funerary and liturgical rites. The scant grave goods in late medieval burials comprise laterally perforated pottery vessels which are usually filled with charcoal. They occur in most regions of western Europe and are interpreted as incense burners but have never been investigated with advanced analytical techniques. We herein present chemical and anthracological results on perforated funerary pots from 4 Wallonian sites dating to the 12–14 th century AD. Chromatographic and mass spectrometric analysis of lipid extracts of the ancient residues and comparison with extracts from four Boswellia species clearly evidence the presence of degraded frankincense in the former, based on characteristic triterpenoids, viz. boswellic and tirucallic acids, and their myriad dehydrated and oxygenated derivatives. Cembrane-type diterpenoids indicate B. sacra (southern Arabia) and B. serrata (India) as possible botanical origins. Furthermore, traces of juniper and possibly pine tar demonstrate that small amounts of locally available fragrances were mixed with frankincense, most likely to reduce its cost. Additionally, markers of ruminant fats in one sample from a domestic context indicate that this vessel was used for food preparation. Anthracological analysis demonstrates that the charcoal was used as fuel only and that no fragrant wood species were burned. The chars derived from local woody plants and were most likely recovered from domestic fires. Furthermore, vessel recycling is indicated by both contextual and biomarker evidence. The results shed a new light on funerary practices in the Middle Ages and at the same time reveal useful insights into the chemistry of burned frankincense. The discovery of novel biomarkers, namely D 2 -boswellic acids and a series of polyunsaturated and aromatic hydrocarbons, demonstrates the high potential for organic chemical analyses of incense residues. Citation: Baeten J, Deforce K, Challe S, De Vos D, Degryse P (2014) Holy Smoke in Medieval Funerary Rites: Chemical Fingerprints of Frankincense in Southern Belgian Incense Burners. PLoS ONE 9(11): e113142. doi:10.1371/journal.pone.0113142 Editor: Roberto Macchiarelli, Universite ´ de Poitiers, France Received June 11, 2014; Accepted October 23, 2014; Published November 12, 2014 Copyright: ß 2014 Baeten et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Data Availability: The authors confirm that all data underlying the findings are fully available without restriction. All relevant data are within the paper and its Supporting Information files. Funding: This research was supported by the Belgian Programme on Interuniversity Poles of Attraction (IAP 7/09, iap-cores.be), the special research fund of the KU Leuven (Centre for Archaeological Sciences, ees.kuleuven.be/cas) and the Research Foundation - Flanders (G.0486.12, www.fwo.be). The Research Foundation - Flanders is acknowledged for enabling the acquisition of a new GC-MS instrument. The other funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. * Email: dirk.devos@biw.kuleuven.be Introduction Frankincense, or olibanum, is an oleogum resin that exudes in pale yellow to red tears from incisions in the bark of certain Boswellia trees (Burseraceae family) thriving in arid regions in the horn of Africa and southern Arabia [1]. It is generally composed of 5–9% essential oil, 65–85% alcohol-soluble resin and the remaining water-soluble gums [2]. The precise chemical compo- sition depends on the botanical species. Most important species are Boswellia serrata (India), B. sacra (Yemen, Oman), B. carterii (Somalia, contentiously considered the same species as B. sacra, e.g. [3]), B. papyrifera (Eritrea, Sudan, Ethiopia) and B. frereana (Somalia) [2,4]. Myrrh is another classical incense source and has often been confused with frankincense. Both oleogum resins have often been loosely designated by the term ‘‘incense’’, particularly in older literature, generating ambiguity as to the exact taxon [2,4]. However, whilst frankincense and myrrh trees both belong to the same Burseraceae family and grow in the same regions (cf. supra), they constitute two separate genera, viz. Boswellia and Commiphora, respectively, and their resins have disparate chemical compositions [1]. Plumes of burning frankincense are associated with perfumes, embalming and religious rituals. Furthermore, its medicinal properties attract much attention nowadays as they did in antiquity [5–7] but the emission of toxic polyaromatic hydrocarbons (PAHs) during incense burning raises some health concerns as well [8,9]. The use of incense has a long history. From the late 4 th millennium BC onwards, Arabian incense burners began to appear and Egyptians travelled great distances to import frankincense and myrrh [5,10,11]. Frankincense was also highly esteemed throughout Assyria, Babylonia, Persia, Greece and the demand reached its peak when Romans burned it in temples, at PLOS ONE | www.plosone.org 1 November 2014 | Volume 9 | Issue 11 | e113142