## 1 Introduction
To validate this hypothesis, it is necessary to confirm that the bone is indeed burnt. However, determining whether a bone is burnt is not always easily achieved based on macroscopic observations since other taphonomic processes may mimic heat-induced changes. Weathering, soil staining, manganese oxide as well as other agents may imitate heat-induced colours displayed by charred and calcined bone [9; 10; 11; 12; 13]. Therefore, the confirmation of a bone's burnt condition benefits from the application of other methods of analysis. In the case of specimen [19-23 AP C16], such validation would enlighten us about the technique used in the manufacturing of the bone artefact. If heat exposure is confirmed, another important question associated with the VNSP artefacts regards the environmental conditions during the burning event. Some of the artefacts display a white colour typical of calcined bone under aerobic conditions. However, several other artefacts show a black colouration which can basically be achieved through two different heat exposure procedures: either by submitting bone to medium temperatures (ca. 300-500 \({}^{\circ}\)C) [14; 15; 16; 17; 18] or by reducing the oxygen available during the burn, as inferred from the work of [PERSON] et al. [19], [PERSON] et al. [20] and [PERSON] et al. [21]. [PERSON] et al. [19] argued that oxygen reducing conditions may explain the incorporation of cyanamide into burnt bone leading to incomplete oxidization of organic matter. According to [PERSON] et al. [22], the formation of cyanamide results from NH\({}_{3}\) released during the burn of organic matter under reducing conditions. Based on recent neutron spectroscopy data obtained for bones burnt under anaerobic conditions (sealed vs. unsealed containers), cyanamide was detected above 650 \({}^{\circ}\)C [21]. Therefore, this reaction must  
Figure 2: The four fragments of cylindrical engraved bone “boxes” from Vila Nova de São Pedro used in this research. (**A**) 19-27 AP C16; (**B**) 19-26 AP C16; (**C**) 19-11 AP C16; (**D**) 19-23 AP C16. occur immediately, at the surface, and soon after the formation of NH\({}_{3}\). Otherwise, the latter would have been removed through evacuation. More recently, [PERSON] et al. [21; 23] observed that cyanamide formation--in the presence of free ammonia formed during the burning process--is associated with incomplete oxidation of organic matter leading to incorporation of CN\({}_{2}\)\({}^{2-}\) ions into bone's inorganic matrix, substituting for OH\({}^{-}\) and yielding cyanamidapatite (Ca\({}_{10}\)(PO\({}_{4}\))\({}_{6}\)CN\({}_{2}\)). This is reflected by distinctive infrared features from CN\({}_{2}\)\({}^{2-}\): at 700 cm\({}^{-1}\) (N-C\(\equiv\)N bending) and 2009 cm\({}^{-1}\) (C\(\equiv\)N stretching). The presence of cyanamide in the infrared spectra can thus be used to identify burns under reducing conditions, possibly exchanging with hydroxyl groups in apatite. The work of [PERSON] et al. [20] with bones burnt under anaerobic conditions suggests another possible useful feature--OH groups. These were absent from their infrared spectra of bone burnt at 900 \({}^{\circ}\)C (bands 630 cm\({}^{-1}\); 3572 cm\({}^{-1}\); 3642 cm\({}^{-1}\)) although they are usually present in bones burnt under aerobic conditions [19; 24; 25]. In this paper, we used Fourier-transform infrared spectroscopy in attenuated total reflectance mode (FTIR-ATR) with the objective of investigating the issues described above. This technique has been routinely applied to the study of bone and is cost-effective, rapid, simple and non-destructive, requiring only a few mg of bone powder [26]. By contrast to solid-state NMR which yields overall information on bone, for each active nucleus probed [27; 28; 29], infrared spectroscopy is able to provide comprehensive data on bone's chemical composition and structure simultaneously, in a straightforward and rapid manner, which renders it ideal for a routine analysis of the effect of heat on these types of samples.