## 1 Introduction  
Bone industries are a core item among 3 rd millennium cal BC productions and integrate some of the most exquisite pieces of the period but are also simple and poorly transformed tools. However, opposite to lithtic or pottery remains, bone artefacts are rarely preserved in the archaeological record since soil acidity tends to lixiviate organic materials. The walled chalcolithic site of Vila Nova de Sao Pedro (VNSP), settled on a hilltop in the Lower Tagus valley basin in a Miocene-Pontian limestone area, is an outstanding case-study due to environmental conditions that allow bone preservation but also because VSNP possesses the largest and richest artefact assemblage of Copper Age Western Iberia [1]. This settlement played a core role as a production, consumption, and redistribution centre during the third millennium cal BC which explains the largest concentration of bone, pottery, flaked/polished stone tools and copper artefacts retrieved at the site [2; 3; 4; 5; 6]. At VSNP, artefacts production depended on local (e.g., limestone, clay, flint) and non-local raw materials (e.g., copper, amphibolite) and the use of controlled fire was mandatory to transform clay into pottery, to melt copper and to heat flint to optimize the _debitage_ process [7]. However, the production of bone utensils is not dependent on fire and Chalcolithic bone industries are usually made upon raw bones and, even in highly transformed pieces such as bone pins or idols/pendants, raw material curation usually does not go beyond the carving and polishing of the bone surfaces. Exceptionally, at VSNP, fire seems to have been involved in the bone industry to produce outstanding pieces from an aesthetic and manufacturing point of view. All required stages of the _chatine operatoire_ to produce bone boxes are recorded at the site and the sharp chromatic contrast between white and black shiny bone surfaces was intended to highlight some of the artefacts as the ones here described. Belonging to the typological class of small \"cylindrical engraved bone/ivory boxes\" [8]--even if both sides of the box are opened and require an organic material to be closed--the VSNP minimum number of 45 elements, cylindrical bones \"boxes\" (MNI), stand as the largest collection in the Iberian Peninsula. Examples of reconstructed bone boxes from VSNP are presented in Figure 1. The functionality of these small cylindrical engraved bone \"boxes\" measuring 4-7 cm in width, 4-8 cm in diameter and 0.5-1 cm in thickness is not clear although some considered it as \"cosmetic boxes\" [8]. Made after the long bones of large mammals (bovids or equids), cylindrical engraved bone \"boxes\" have been recorded for the third millennium cal BC in domestic and, more frequently, in funerary contexts from the Portuguese Lower Estremadura, being usually recovered in very small numbers. The VSNP assemblage is so far exceptional attending to its proportion, to the fact that all stages of production are recorded at the site but also due to crafts procedures. The potential use of fire to change bone colour and thus the final appearance of the finished product has not been recorded in other cylindrical engraved bone boxes from Lower Estremadura sites. According to published data, no significant colour changes are displayed by the latter artefacts. Four fragments of cylindrical engraved bone \"boxes\" retrieved during the [PERSON]'s archaeological excavations were selected to attempt to understand how fire was potentially used to manufacture these prestigious artefacts. The manufacturing of these bone artefacts involved carving and, apparently, heat exposure. However, if fire was used, the order in which those tasks were accomplished is unknown. One of the bone pieces-- [19-23 AP C16] --appears to be only partially burnt  
Figure 1: Examples of reconstructed cylindrical bone boxes from Vila Nova de São Pedro (Photo: VSNP3000 project). pointing to the possibility that the bone was initially carved and only then subjected to a heat treatment leading to a dark shade (Figure 2D).