Stéphanie Leroy

Sylvain Bauvais

Emmanuelle Delqué-Količ

Mitch Hendrickson

Nicolas Josso

Jean Pascal Dumoulin

Dominique Soutif

First experimental reconstruction of an Angkorian iron furnace (13 th c.-14 th centuries CE): Archaeological and Archaeometric Implications

Keywords: Iron, Angkorian furnace, Archaeometallurgy, Experimental smelt, Integrated experimental research

The region around Phnom Dek in Northern Cambodia represents a vast metallurgical landscape with evidence for mining and smelting of iron spanning over a millennium of smelting activities (7 th to 20 th centuries CE). Research conducted over the past decade in this region has expanded our understanding of the resources, production, technological evidence and furnace structures used during the Angkor period (11 th c.-14 th c.). In December 2018, a first experimental attempt at reducing iron ore mined from the historic source at Phnom Dek was conducted at the Ecole Française d'Extrême-Orient (EFEO) Center in Siem Reap/Angkor (Cambodia). The experimental research was designed to achieve several interconnected objectives. The aim of our study is not only to address technical questions relative to the metallurgical traits of the furnace and the metallurgical process employed during the late Angkor period, but also to provide new data to clarify the interpretations resulting from the provenance and iron dating analyses that assist in interpretations relating to production and consumption practices. Both the archaeological evidence and ethnographic descriptions were combined to reproduce the experimental furnace. This paper summarizes the preliminary results and provides information on the late Angkorian smelting process and on the accuracy and variabilities of the archaeometric data including provenance and iron dating.

Introduction

The Phnom Dek region in northern Cambodia is a vast metallurgical landscape used by iron smelters for over a millennium (7 th to 20 th centuries CE) (Figure 1). Research about this region has highlighted the scope of iron production, its impact on the development of Khmer history as well as details about local smelting practices. Surveys conducted by European mining and civil engineers during the 19 th and 20 th c. documented the presence of multiple slag mounds and iron ore sources including the largest at Phnom Dek (the "Iron Mountain"), while French government expeditions generated the initial records of the Kuay people, an ethnic minority who worked iron here since at least the 16 th c. [START_REF] Aymonier | Le Cambodge: Le royaume actuel[END_REF][START_REF] Dufossé | Monographie des peuplades Kouys du Cambodge[END_REF][START_REF] Hansen | Exploration du Tonlé-Repau, du Stung-Sen et des pays Kouys[END_REF][START_REF] Harmand | Voyage au Cambodge[END_REF][START_REF] Khin | Chroniques royales du Cambodge: De Bañā Yāt à la prise de Laṅvaek (de 1417 à 1595)[END_REF][START_REF] Moura | Notes sur le minerai de fer de Compong Soai au Cambodge[END_REF][START_REF] Saladin | Mémoire sur l'exploration des gîtes de combustibles et de quelques-uns des gîtesmétallifères de l'Indo-Chine, extrait du Rapport adressé aux ministres de la Marine et des Travauxpublics et au gouverneur de la Cochinchine[END_REF]. More recently, extensive field research and multidisciplinary analysis of metallurgical by-products and iron crampons from temple restorations in Angkor have successfully revealed shifting qualities/preferences of iron products and an increased reliance on metal sourced from the Phnom Dek region [START_REF] Hendrickson | Smelting in the Shadow of the Iron Mountain: Preliminary field investigation of the industrial landscape around Phnom Dek, Cambodia (9th to 20th centuries CE)[END_REF][START_REF] Leroy | The ties that bind: archaeometallurgical typology of architectural crampons as a method for reconstructing the iron economy of Angkor, Cambodia[END_REF]. This included shifts in production intensity between the 11 th and 15 th c. showing correlations with the expansions and ultimate decline of Angkor [START_REF] Hendrickson | Smelting in the Shadow of the Iron Mountain: Preliminary field investigation of the industrial landscape around Phnom Dek, Cambodia (9th to 20th centuries CE)[END_REF][START_REF] Hendrickson | Sparks and needles: Seeking catalysts of state expansions, a case study of technological interaction at Angkor, Cambodia (9th to 13th centuries CE)[END_REF]. Reconstruction of smelting practices necessary to refine these regional-scale studies has been hampered by the lack of archaeological furnaces and the incomplete record of Kuay techniques as a potential analogue for earlier systems in the Phnom Dek region [START_REF] Dupaigne | Les Maîtres du fer et du feu : étude de la métallurgie du fer chez les Koouy du nord du Cambodge, dans le contexte historique et ethnographique de l'ensemble khmer[END_REF][START_REF] Lévy | Recherches préhistoriques dans la région de Mlu Prei : accompagnées de comparaisons archéologiques et suivies d'un vocabulaire français-kuy[END_REF]Pryce et al., 2 2014). Excavation of three furnace bases at Tonle Bak (13 th -14 th c.) 2km south of Phnom Dek [START_REF] Hendrickson | Forging empire: Angkorian iron smelting, community and ritual practice at Tonle Bak[END_REF] provides the first opportunity to begin modelling the operation and products of an Angkor period installation using experimental methods. This paper summarizes the preliminary results of an experimental smelt conducted at the Ecole Française d'Extrême-Orient (EFEO) Center in Siem Reap/Angkor in December 2018 (Experimental Archaeology festival) as part of the IRANGKOR research program. Our work represents a first attempt to reduce ore mined from the historic source at Phnom Dek with the goal of testing hypotheses on the metallurgical traits of the furnace and the smelting process as well as providing information on the accuracy and variabilities of archaeometric data including provenance and direct dating of iron products. While issues of design and furnace charging became apparent, the results from this initial test are a significant step for using experimental research to expand on future studies of past metallurgical practices and modern interpretations.

Figure 1: Location of the Phnom Dek (PD) area, the place of collect of the iron ores for this experimental research and the archaeological sites mentioned in the text.

Archaeological and Archaeometric Questions

Before examining the results of the experimental smelt, it is necessary to identify some of the key questions that arise from the archaeometric approaches (e.g., provenance and radiocarbon dating analyses) we use to interpret production and consumption practices based on the archaeological record. Provenance investigation can be based on the investigation of the chemical relationships between the ores, the smelting slag and slag inclusions (SI) entrapped in the iron artefacts. Previous research has demonstrated the possibility of identifying consistent signatures associated with a particular smelting process or geographic origin by defining a combination of oxides (mainly the non-reduced compounds -NRCs-) or oxides ratios. Determining and comparing the chemical signatures in ores and/or slag is an essential step in attempts to establish provenance [START_REF] Buchwald | Slag analysis as a method for the characterization and provenancing of ancient iron objects[END_REF][START_REF] Coustures | The use of trace element analysis of entrapped slag inclusions to establish ore -Bar iron links: examples from two Gallo-Roman iron-making sites in France (Les Martys, Montagne noire, and les Ferrys, Loiret)[END_REF]Leroy et al., 2012;[START_REF] Charlton | The last frontier in "sourcing": The hopes, constraints and future for iron provenance research[END_REF]. Direct correlation of chemical signatures, especially those based on the major elements, can be complicated by the fact that the NRC ratios can be highly scattered due to the chemical influence of parent materials such as furnace components and fuels [START_REF] Blakelock | Slag inclusions in iron objects and the quest for provenance: an experiment and a case study[END_REF][START_REF] Charlton | Investigating the production provenance of iron artifacts with multivariate methods[END_REF]. Our experimental contribution aims at helping to test and specify these patterns in the case of the Angkorian technology. As the resulting experimental bloom was not hammered to produce an iron product, this study is restricted to the patterns of slag composition resulting from the bloomery smelting process. Studies of iron production systems are also complemented by recent developments in direct dating of iron alloys through radiocarbon analysis. The principle of 14C dating of iron relies on the presence of carbon atoms in the metal structure (Fe3C) originating from the CO-rich atmosphere generated by the wood charcoal used as fuel during the smelting process. Thus, the radiocarbon age of the alloy is related to the radiocarbon age of the wood charcoal and more or less shifted from the reduction event according to the age of the fuel. Nevertheless, we can assume that this effect is reduced by the fact that when burning an entire trunk or a collection of trees, the outer rings of the trunk and branches, i.e. the youngest wood, outweigh the oldest heartwood [START_REF] Dee | High-Precision Bayesian Modeling of Samples Susceptible to Inbuilt Age[END_REF]. Precise calculation of this wood-age offset is impossible but may be estimated by anthracological studies of the charcoal remains, by analogy with ethnographic cases if they exist or by experimental reconstitutions. In 2011, some of the authors carried out an experimental smelting [START_REF] Leroy | Datation radiocarbone des alliages ferreux anciens[END_REF]S. Leroy et al., 2015b), involving carbonated ore (siderite) and young branch wood (≤ 10 yrs old), whose purpose was to investigate a potential ageing effect of the carbonated ore on the radiocarbon date of the metal produced [START_REF] Oinonen | Radiocarbon Dating of Iron: A Northern Contribution[END_REF]. The final iron date falls in the last 10 years range of the wood charcoal showing the predominance of the fuel in the production of a CO-rich atmosphere in the furnace. Nevertheless, the "old wood effect" in iron dating was not directly investigated and it seemed obvious to integrate this aspect in the experimental research. Within these broader archaeometallurgical issues, the experimental smelt seeks to enhance our understanding of Cambodian iron production through several interconnected objectives. First, the evidence from the Tonle Bak excavation is used to tease out the technical parameters underlying the smelting process employed during the 13 th c. The archaeological data are still limited and many questions remain about the Angkorian furnace characteristics such as about the exact number and placement of tuyères, wall height, quantity of raw materials used per operation, type of the ventilation, and duration of a single smelt. Given that furnace walls in the Cambodian procedure were destroyed to remove the bloom, there is no certainty of finding new data on these elements in the future and an experimental approach remains the best way to test any structural assumptions. Second, investigation into the products and waste from the experiment will be used to determine how they were manufactured (e.g., redox conditions, technical gestures). Incremental feedback between archaeological and archaeometric observations are combined to provide new evidence about the furnace operation. Third, chemical and radiocarbon dating investigation of this experimental assemblage can help to provide new data to clarify the interpretations resulting from the provenance and dating analyses within the context of the Angkorian technology. Finally, the experiments at the EFEO center are designed to provide not only a better understanding of the technologies used in medieval Cambodia, but to also fulfill important community and educational objectives. These experiments are an excellent opportunity for training and knowledge transfer and serve as an unparalleled medium to help young Khmer archaeologists and students understand the longforgotten technologies of their past and how to recognize them in the field.

Archaeological and Archaeometric Evidence: The Late Angkor Period

Smelting Process

Research conducted over the past decade has expanded our understanding of the resources, technological materials and furnace structures used in the Phnom Dek region [START_REF] Hendrickson | Smelting in the Shadow of the Iron Mountain: Preliminary field investigation of the industrial landscape around Phnom Dek, Cambodia (9th to 20th centuries CE)[END_REF][START_REF] Hendrickson | Sparks and needles: Seeking catalysts of state expansions, a case study of technological interaction at Angkor, Cambodia (9th to 13th centuries CE)[END_REF][START_REF] Pryce | The Iron Kuay of Cambodia: tracing the role of peripheral populations in Angkorian to colonial Cambodia via a 1200 year old industrial landscape[END_REF]. By using this localised evidence in our experimental smelt we have a greater opportunity to replicate and inform on patterns seen in the archaeological record.

Resources

Phnom Dek is one of several ore bodies in the region. It became a preferred source during the Angkor period and specifically during the 13 th c. [START_REF] Hendrickson | Sparks and needles: Seeking catalysts of state expansions, a case study of technological interaction at Angkor, Cambodia (9th to 13th centuries CE)[END_REF][START_REF] Leroy | The ties that bind: archaeometallurgical typology of architectural crampons as a method for reconstructing the iron economy of Angkor, Cambodia[END_REF]. The composition of this ore was first chemically determined by French specialists as a massive hematite ore deposit containing two types of minerals. The first type is a mix of magnetite (Fe3O4) and hematite (Fe2O3), rich in iron (>70wt%), while the second type is composed of limonite (mainly composed of goethite FeOOH) with a lower iron content (30-45wt%) [START_REF] Caillère | Examen microscopique de trois échantillons du minerai de fer (Cambodge)[END_REF][START_REF] Saladin | Mémoire sur l'exploration des gîtes de combustibles et de quelques-uns des gîtesmétallifères de l'Indo-Chine, extrait du Rapport adressé aux ministres de la Marine et des Travauxpublics et au gouverneur de la Cochinchine[END_REF]. Recent analysis of the iron ores in the frame of IRANGKOR confirm these observations and will not be detailed in this article. No ore processing area was found on site but small roasted ore fragments found on Tonle Bak suggest that the size of ore particles added to the furnace was approximately 1-2 cm in diameter. For the time being, no data are currently available on the identification of the charcoal species used for the fuel, but ongoing studies will provide first results in the region in the near future.

Technological Evidence

The traditional iron technology in Cambodia involves direct smelting in low furnaces and the production of tap slag. The smelting slag from the surveyed sites, though dated from different periods, share a similar morphology showing an accumulation of different layers of flow shaped by the slag pit (see Figure 2) [START_REF] Hendrickson | Forging empire: Angkorian iron smelting, community and ritual practice at Tonle Bak[END_REF]. Morphological characteristics show low viscosity, and slag seems to separate cleanly from the bloom. The Reducible Iron Index (see [START_REF] Charlton | Explaining the evolution of ironmaking recipes -An example from northwest Wales[END_REF]), which provides information on the furnace redox conditions, calculated for a preliminary set of samples from late Angkorian/Kuay sites indicates the incomplete reduction of available FeO [START_REF] Pryce | The Iron Kuay of Cambodia: tracing the role of peripheral populations in Angkorian to colonial Cambodia via a 1200 year old industrial landscape[END_REF]. Moreover, intensive metallographic analysis of metal produced during the Angkor period revealed that from the early 12 th c., the nature of the alloy from the iron-making workshops of the Phnom Dek area, probably including the Tonle Bak sites, is rather homogeneous with low-carbon content [START_REF] Leroy | The ties that bind: archaeometallurgical typology of architectural crampons as a method for reconstructing the iron economy of Angkor, Cambodia[END_REF]. Overall, the results are consistent with an iron-making process favoring the production of low-carbon blooms rather than natural steel.

Furnace Structure

In 2017, excavations at Tonle Bak provided the first evidence for furnace structures dating to the Angkor period (13 th -14 th c.) [START_REF] Hendrickson | Forging empire: Angkorian iron smelting, community and ritual practice at Tonle Bak[END_REF]. The three furnaces are rectilinear in shape and approximately 2m long and 1m wide. Only the base of the furnace is still visible with the eastern end shaped like an apse while the western end extends slopes down with a central channel that flows into a slag pit (Figure 3). Lack of walls and tuyères indicate that walls were broken in order to remove the bloom at the end of the smelt. This practice explains the considerable quantities of wall and tuyère fragments found on the surface of slag mounds across Phnom Dek. The metallurgical traits of the Angkorian tuyères (11 th -13 th c) are classified in the medium-gauge category (Internal Diameter ID ranging from 2.3 to 3 cm; External Diameter ED from 4.5 to 6 cm) [START_REF] Pryce | The Iron Kuay of Cambodia: tracing the role of peripheral populations in Angkorian to colonial Cambodia via a 1200 year old industrial landscape[END_REF]. Unfortunately, the incomplete nature of technological evidence at Tonle Bak (e.g., lack of information about quantity and placement of tuyères, wall dimensions) means that reconstruction of Angkorian smelting practice cannot solely rely on the archaeological record.

Ethnographic Evidence

The 19 th and 20 th c. ethnographic accounts describing Kuay iron smelting practice provide another important source of evidence about the construction and operation of furnaces in the Phnom Dek region [START_REF] Dufossé | Monographie des peuplades Kouys du Cambodge[END_REF]. The long-term Kuay presence combined with similarities in the use of large numbers of tuyères, basic furnace shape and preliminary metallurgical analyses indicating a possible conservatism in late Angkor and Kuay iron smelting parameters [START_REF] Pryce | The Iron Kuay of Cambodia: tracing the role of peripheral populations in Angkorian to colonial Cambodia via a 1200 year old industrial landscape[END_REF] suggests continuities in practice suitable for incorporating into the experimental reconstruction.

Ore and charcoal preparation

The two mineralogical distinctions identified for the Phnom Dek deposit were similarly noted by the Kuay who divided ores based on appearance and weight into the "heavy stones" (thma thngon) and the "light stones" (thma sral) whose colour is slightly different. The last type seems to be preferred by the Kuays for the smelting [START_REF] Boulangier | Un Hiver au Cambodge. Chasses au tigre, à l'éléphant et au buffle sauvage[END_REF][START_REF] Harmand | Voyage au Cambodge[END_REF][START_REF] Moura | Notes sur le minerai de fer de Compong Soai au Cambodge[END_REF]. Once procured, the Kuay would roast the ore [START_REF] Harmand | Voyage au Cambodge[END_REF][START_REF] Moura | Notes sur le minerai de fer de Compong Soai au Cambodge[END_REF] to transform it into "small grains" [START_REF] Boulangier | Les mines de fer de Compong-Swai[END_REF]. Charcoal production using the nearby forest was carried out shortly before the smelt as charcoal cannot be stored in advance nor can it be made in the rainy season. According to Dupaigne [START_REF] Dupaigne | Les Maîtres du fer et du feu : étude de la métallurgie du fer chez les Koouy du nord du Cambodge, dans le contexte historique et ethnographique de l'ensemble khmer[END_REF], who interviewed chief smelters nearly 30 years after the last firing, the preferred tree species to produce charcoal are krokas (Caesalpiniaceae sindora cochinchinensis Baill.), popil (Dipterocarpaceae shorea talura Roxb.) and chramas (Dipterocarpaceae vatica odorata Griff.). To make the charcoal, a pile of wood is built on the ground, ignited at the base and covered with soil to prevent oxygen from entering the structure and to thus avoid the complete burning of the wood [START_REF] Hansen | Exploration du Tonlé-Repau, du Stung-Sen et des pays Kouys[END_REF]. Descriptions made at the end of the 19th c. all describe the same quantity of raw materials used for the smelting process: between 300 and 420 kg of iron ore is required and the volume of charcoal introduced is twice that of the ore. The expected yield is perhaps 40-50% iron: 85 to 150 kg of iron is thus obtained [START_REF] Dupaigne | Les maîtres du fer et du feu dans le royaume d'Angkor[END_REF].

Description of the Kuay furnace

The furnace had a rectangular-shaped furnace chamber with dimensions ranging from 2 to 3 m in length and from 1 to 2 m in width, with walls extending up to 1 m and two holes, at both ends, for the evacuation of the slag during the smelting process [START_REF] Bouillevaux | Voyage dans l'Indo-Chine, 1848-1856 avec carte du Cambodge et d'une partie des royaumes limitrophes[END_REF][START_REF] Boulangier | Un Hiver au Cambodge. Chasses au tigre, à l'éléphant et au buffle sauvage[END_REF][START_REF] Boulangier | Les mines de fer de Compong-Swai[END_REF][START_REF] Dupaigne | Les Maîtres du fer et du feu : étude de la métallurgie du fer chez les Koouy du nord du Cambodge, dans le contexte historique et ethnographique de l'ensemble khmer[END_REF][START_REF] Fortoul | Notes sur le fer au nord Cambodge[END_REF][START_REF] Harmand | Voyage au Cambodge[END_REF][START_REF] Moura | Le royaume du Cambodge[END_REF]. A 20 to 30 cm wide trench dug along the long axis of the furnace was observed, most likely to facilitate evacuation of slag. Walls were built from a local yellow clay that is abundant in the region [START_REF] Boulangier | Les mines de fer de Compong-Swai[END_REF].

Tuyères and air supply system

The air supply system is one of the unique characteristics of the Kuay smelting process. Bellows are located on the long sides of the furnace and air is passed initially through bamboo tubes and then into clay tuyères. The total number of tuyères per side is between 20 and 30. They are fixed at half the height of the wall in a fanning arrangement above the middle of the base furnace [START_REF] Dupaigne | Les Maîtres du fer et du feu : étude de la métallurgie du fer chez les Koouy du nord du Cambodge, dans le contexte historique et ethnographique de l'ensemble khmer[END_REF][START_REF] Harmand | Voyage au Cambodge[END_REF]. A gap of 2 cm between the bamboo tubes and tuyères allows air to be brought into the bellows before being forced back into the furnace. This ventilation system may cause a significant loss of draught [START_REF] Boulangier | Les mines de fer de Compong-Swai[END_REF][START_REF] Harmand | Voyage au Cambodge[END_REF]. Compared to the Angkorian tuyères, the tuyères associated with Kuay sites have smaller standardised bore with an internal diameter ranging from 2 to 2.5 cm and an external diameter between 3 and 4 cm [START_REF] Pryce | The Iron Kuay of Cambodia: tracing the role of peripheral populations in Angkorian to colonial Cambodia via a 1200 year old industrial landscape[END_REF]. Regardless of size, tuyère manufacture involves wrapping wet clay around a rattan wood about 1 meter long. Once firmed, the clay was removed from the wood, then left to dry 2 hours in the sun before being dried for 24 hours [START_REF] Dupaigne | Les Maîtres du fer et du feu : étude de la métallurgie du fer chez les Koouy du nord du Cambodge, dans le contexte historique et ethnographique de l'ensemble khmer[END_REF]. Dupaigne). Remaining wood walls from the air supply system exhibit the numerous holes for the air supply.

The Experimental Smelt

Recognizing the limitations of ethnographic analogy and potential technical differences, we used Kuay accounts on ore and charcoal preparation, furnace operation and air supply to complement the missing archaeological data. For some settings partially documented by both archaeology and ethnographic accounts, other technical choices already experienced by the authors in different contexts have been made while being aware that these choices may interfere the experiment's result. Nevertheless, this provides favorable conditions for a successful smelt, which remains a primary objective of this first experimental attempt.

The furnace

Archaeological evidence and ethnographic descriptions were combined to reproduce the experimental furnace at the EFEO Siem Reap/Angkor in December 2018. As this was the first attempt to smelt iron and given the wide range of potential parameters to control, we selected to reproduce the structure and materials at a 1:2 scale (Table 1). The experimental furnace had a rectangular internal shape with two apsidal ends and an internal dimension of 0.5x1 m (Figure 5). The total possible load height ranged from 0.7 to 0.8 m depending on the internal 5° slope of the furnace base. Ten holes for ventilation were made on the longest sides of the furnace walls, placed 20 cm above the external base. There is no archaeological evidence for the inclination/position for the Angkorian tuyères. In the Kuay manner they are described as being fixed mid-way in the wall [START_REF] Dupaigne | Les Maîtres du fer et du feu : étude de la métallurgie du fer chez les Koouy du nord du Cambodge, dans le contexte historique et ethnographique de l'ensemble khmer[END_REF]. Nevertheless, this position was not embraced into the experimental furnace setting for two main reasons. First, tuyère position and angle relative to the fuel bed are important for controlling the size and shape of the combustion zone of the furnace. We did not master the Kuay configuration sufficiently to meet with this condition. Second, in the lack of additional compositional data on technical ceramics, the risk of clogging the tuyères during smelting was too high with this configuration.The choice for inclination and position was thus dictated by knowledge acquired by the authors in other archaeological contexts, particularly in contexts dating from medieval times in Europe (M. Leroy et al., 2015) p. 156). The angle of inclination of the tuyères was approximately 8°, and they were therefore fixed closer to the external base of the wall. As suggested by the ethnographic data, the tuyères were arranged in a fanning orientation to cover the entire internal surface of the furnace and were separated from each other in the centre by a distance of 10 cm. The tuyères were made from a clay plate rolled around a wooden handle with a diameter of 2.2 cm using a plastic sheet. The tuyères were then dried around the wood until they became rigid enough to allow for its extraction (3 to 4 hours in the sun).

A last drying of 24 hours in a ventilated space makes the tuyères solid enough and ready to use. Their final dimensions are ca. 50 cm long, with an internal diameter of ca. 2.2 cm and an external diameter of ca. 5 cm. This resulting morphology is therefore between the archaeological data and the ethnographic ones. The air supply system was an important focus of experimentation due to the difficulty to set up the very delicate bellows and ventilation system as described in the ethnographic accounts. To generate sufficient heat within the furnace, limit the random parameters and avoid issues due to changing temperatures, the ventilation of the furnace was produced by electric fans that created equal air pressure for each tuyère.

Clay 10

The clay for the furnace walls and tuyères came from a local brick factory in Siem Reap. Different 11 proportions of local sand were mixed with the clay for each technical component. For the furnace walls, 12 25% sand was introduced for the overall assembly and the internal surfaces of the furnace (walls and 13 floor) were then coated with a liquid clay mixed with 50% sand. The furnace was constructed two months 14 before the experimental smelt. The tuyères need to be particularly refractory as they are in contact with the 15 hottest area of the furnace (around 1300 to 1400°C). To prevent clogging, the clay was therefore saturated 16

with sand (around 50 to 60%) to increase resistance during the smelt and to avoid them collapsing on 17 themselves. The clay as well as the technical ceramics from the experiment are planned to be investigated 18 by the ArAr laboratory (Archaeology and Archaeometry) in Lyon (France). 19

Charcoal

20

A quantity of 600 kg of charcoal was purchased from a producer located 20 km north of Siem Reap, who 21 obtains wood from forested areas in northern Cambodia. The exact species are not precisely known but the 22 charcoal producers surveyed for this experiment frequently mentioned the names phchök (Shorea Obtusa) 23 and châmbâk' (Irvingia Malayana). These are hardwood species largely used in Cambodia for general 24 construction as well as charcoal production [START_REF] Francois | Charcoal, Forest and Livelihoods in the Northern Cardamoms, Cambodia -Participatory Impact Assessment of Charcoal production using Global Forest Watch[END_REF]. Modern charcoal is made in reusable 25 charcoal kilns built with clay, mud or termite soil. The carbonised logs, approximately 60 cm length and 26 between 10 and 50 cm in diameter, were cut into pieces of 5-8 cm at the maximum. 27 28 Figure 6: The different stages of preparation for the ore, charcoal and tuyères.

The Smelting Process

The furnace was lit in the morning of December 5 and the firing was conducted over a period of 12 hours, including 1 hour of heating and 1 hour of final combustion with no ore charge. Temperatures were recorded each time a new charge of ore and charcoal was added using two thermocouples placed at the rear apse of the furnace (Figure 7). One 'low' probe (T1) was placed 22 cm from ground level and 48 cm from the top and a second 'high' probe (T2) was placed 43 cm from ground level and 27 cm from the top of the wall. T1, which was supposed to record the highest temperature, could not be placed at the level of the air intakes as this was also the level at which the metal and slag formed. For this reason, the temperatures recorded are well below the maximum temperatures reached. We used ethnographic data for the quantities of raw materials. Thus, a final fuel-to-ore ratio of 2:1 was selected for the smelt, while studies of the known slag compositional data for 13 th c. sites appear to favour a 1:1 ratio (see above). Indeed, previous bloomery experiments in other contexts have shown that a ratio close to 2:1 is ideal for producing high-steel metal [START_REF] Crew | Cast iron from a bloomery furnace[END_REF][START_REF] Tylecote | The mechanism of the bloomery process in shaft furnace[END_REF]). Nevertheless, these conditions remain to be confirmed especially since the observations were made for a different metallurgical process. As a first experiment with a wide range of unknown parameters, we preferred to opt for a 2:1 ratio in order to ensure a suitably reducing atmosphere and meet the conditions to produce iron. Charcoal and ore loads were added every 20 to 25 minutes. The first and second charges incorporated 6 kg of ore each and subsequent additions of 4 kg were made, up to a total of 96 kg. After 4 hours and 30 minutes of reduction, a first and only run of tap slag was evacuated through the front hole of the furnace. Slag formation after this event only accumulated at the bottom of the structure, mixing with metal, slag, charcoal and tuyères. At the end of the process, the furnace was opened by breaking the walls to extract the bloom. The final mass comprised of dense slag, light slag and metal that had collected on the ends of the tuyères. This mixture issue may be due to several parameters including the blowing technique, position of the tuyères as well as the slope of the furnace base. The following morning, the light and bubbly slag was extracted and about 30 kg of dense, metal-rich masses could be separated and individualised into seven blocks. Most of the slag was furnace slag that accumulated around the tuyères, adhering to the furnace wall, or entrapped in the upper part of the bloom. A systematic sorting and precise inventory of the remains of the experimental furnace, wastes, and raw metal allowed us to select specimens for a preliminary investigation at the Archaeomaterials and Alteration Prediction Laboratory of the Institute of Archaeomaterials Research (LAPA-IRAMAT) and at the Laboratory for the Measurement of Carbon-14 (LMC14-LSCE).

Methods

The results of the experimental smelt were then examined within the framework of the technological and chronological analyses used for archaeological remains. By doing this, we provide a direct test of the analyses and shed light on the impact of smelting techniques on the final metal and by-products from the experimental smelt.

6.1 Macroscopic and microscopic analyses Morphological characteristics were described first to inform on the nature of the waste products and metal formation. The petrographic and metallographic structures were then investigated by microscopic observations after cutting, embedding and polishing of the selected samples to a grain size of 1µm. For iron, after etching with a suitable reagent (Nital -5% nitric acid diluted in ethanol), the nature of the alloy of the raw metal was determined. A systematic protocol developed at LAPA-IRAMAT acquires mosaics at X5 magnification at each step of the analysis to generate a holistic view of the entire sample and to calculate elements proportions. Optical microscopy of iron and slag samples was done using a Zeiss AxioImager A2m Vario microscope and Zen2 Core software.

Chemical analyses

Major chemical analyses of ore, slag and slag incorporated in the bloom were conducted to define their respective chemical signatures and explore the relationships between them. Iron ore fragments were analysed by ICP-OES and ICP-MS in the Service d'Analyse des Roches et des Minéraux (SARM-CRPG) (France) [START_REF] Carignan | Routine Analyses of Trace Elements in Geological Samples using Flow Injection and Low Pressure On-Line Liquid Chromatography Coupled to ICP-MS: A Study of Geochemical Reference Materials BR, DR-N, UB-N, AN-G and GH[END_REF]. Chemical investigation of major elements (> 0.5 wt.%) of representative areas of slag samples and slag incorporated in the bloom pieces was completed by energy dispersive X-ray spectrometry (EDX with silicon drift detector [SDD] large window allowing counting rates about 90,000 c/s) coupled to a scanning electron microscope (SEM-FEG JEOL 7001-F). Each slag sample was subjected to scans of 1 mm 2 . Analyses of the slag from the bloom involved selecting areas of 300x300 µm, in which all the mineral phases type are present. The raw NRC data were log-ratio transformed to obtain sub-compositional values (namely XE) to compare the element ratios and perform multivariate analysis [START_REF] Aitchison | Some comments on compositional data analysis in archaeometry, in particular the fallacies in Tangri and Wright's dismissal of logratio analysis[END_REF]Leroy et al., 2012). Principal component analysis (PCA with Pearson correlation coefficients) was conducted to evaluate the dispersion of the NRC ratios and highlight the transformation of the chemical signatures from ores to bloom pieces. Since MnO is an ore-related compound, the comparison focused on those that may be subject to compositional variations within the smelting system: Al2O3, CaO, K2O, MgO, SiO2.

Radiocarbon analyses

The charcoal samples were pretreated using the Acid (HCl)-Alkali (NaOH)-Acid (HCl) protocol to remove carbonates and organic components from the soil [START_REF] Dumoulin | Status Report on Sample Preparation Protocols Developed at the LMC14 Laboratory, Saclay, France: From Sample Collection to 14C AMS Measurement[END_REF]. For the radiocarbon dating of ancient iron alloys, the methodology requires detailed metallographic and SI investigation (S. Leroy et al., 2015b). Iron particles were collected in the carburised areas with CoB coated drills. Both iron and charcoal samples were then combusted in sealed tubes with CuO and Ag wire at 850°C for 5 hours to produce CO2. CO2 gas was reduced into graphite to form targets for 14 C measurements in the Artemis AMS facility of the LMC14-LSCE [START_REF] Moreau | Research and Development of the Artemis 14C AMS Facility: Status Report[END_REF]. The 14 C contents measured for the samples were converted into calendar years thanks to the post-bomb atmospheric curve of our region of interest [START_REF] Hua | Atmospheric Radiocarbon for the Period 1950-2010[END_REF] complemented by the Hammer and Levin dataset [START_REF] Levin | Atmospheric Δ14CO2 trend in Western European background air from 2000 to[END_REF][START_REF] Hammer | Monthly mean atmospheric D14CO2 at Jungfraujoch and Schauinsland from 1986 to[END_REF] and by LMC14 measurements on 2017 and 2018 nuts. As suggested by Hua (personal communication), a F 14 C regional offset of + 0.0025 was added to the calibration data for the 2005-2018. These data were implemented in the OxCal v4.3 calibration program [START_REF] Ramsey | Bayesian Analysis of Radiocarbon Dates[END_REF].

Measurements and discussion

7.1 Quality of raw iron and slag Of the 29.8 kg crude reduction mass, two morphological types were obtained and a block of each was analysed (Figure 8). Mass 1 consists of dense, smooth-looking flows and corresponds to a metal that has passed into a liquid state. Mass 2, by contrast is more similar to products from bloomery furnaces that have a more or less spherical or calotte-like morphology and irregular, jagged exterior. Both masses were cut transversely to examine their internal structure (see Figure 8). Figure 8: Morphological aspects of Mass 1 (left) and Mass 2 (right). Mass 1 weighs 3980 g and is elongated in shape, 37.7 cm long, 17.5 cm wide and 7.6 cm thick. Mass 2 weighs 5990 g with a length of 24.3 cm, a width of 20.9 cm and a thickness of 14.4 cm. The red dashed lines show the cutting sections. The polished section of Mass 1 contains a majority of metallic areas (69%) covered with large areas of slag (4%) and charcoal (9%). The outline of the metal zones is very regular and appears to be composed of several superimposed metal "castings". The metal itself is mainly composed of cast iron and hypereutectoid steel (Figure 9). Mass 2 is rather hemispherical or bole-shaped with very irregular external surfaces and contains numerous charcoal fragments. The metal parts, slag fragments and porosities within the mass are irregularly shaped and numerous (equal proportions of metal 31% and slag 25%). The metal appears to be very homogeneous and composed of 27% hypereutectoid steel and of 0.8%C eutectoid steel (Figure 10). These indices suggest that the metal has not reached its melting point and, consequently, is less carburised than Mass 1.

Overall, Mass 1 contains too much carbon and would be considered unsuitable for forging and therefore rejected by both modern and 13 th c. Angkorian smiths. The hypereutectoid metal of Mass 2 could be forged by highly skilled and specialised craftsmen but this bloom would be generally unsuitable as a basis for a final product for everyday use. Microscopic analyses of ten slag pieces (tap and furnace slags) reveal a clean fayalitic microstructure depleted in iron oxide with nearly no wüstite (Figure 11). This is coherent with high reduction conditions in the furnace and a tendency toward production of a high carbon metal. Overall, the thermochemical profile of the furnace, slag characteristics, and bloom-slag separation clearly show that the experiment is not yet representative of the Angkorian smelting process. The technical choices made by the authors unsurprisingly hindered the final outcome but also provide clues about where changes need to be effected. Most obvious is that several aspects of the air delivery system were inadequate. Tuyères that failed to melt during the operation quickly became partially blocked by the accumulation of slag at the bottom of the furnace. This points to both an incorrect tuyère inclination and clay composition used to make them. Following some ethnographic accounts, the inclination and placement of the tuyères should arrive at the mid-height of the walls relative to the outside of the furnace. A tuyère and wall fragment recovered from Sanlong Jaya, a 20 th c. Kuay smelting site near Phnom Dek [START_REF] Pryce | The Iron Kuay of Cambodia: tracing the role of peripheral populations in Angkorian to colonial Cambodia via a 1200 year old industrial landscape[END_REF] may indicate the use of a 45° angle for the tuyères. This new positioning combined with a decreased ratio of sand in the clay, or a different nature of the clay, would allow the tuyères to melt without collapsing on themselves and reduce their size as the metal mass grows inside the furnace. This differences in composition between tuyères and furnace fragments seems to be in line with observations made by [START_REF] Pryce | The Iron Kuay of Cambodia: tracing the role of peripheral populations in Angkorian to colonial Cambodia via a 1200 year old industrial landscape[END_REF] who noted that the tuyère clays contain higher alumina content relative to furnace clays. Nevertheless, it seems that this "alumina enrichment" would not increase their heat resistance during the smelt, it could rather reflect the absence of adding sand for the tuyères compared to the furnace clay. In the light of these new observations, it is fundamental to complete the compositional data on the clay used for both the walls and the tuyères from archaeological sites to provide new data on the technical choices followed by the smelters. A more complete study (DRX, XRF) of the clay used in the manufacture of technical ceramics is planned for later this year and will be carried out in collaboration with the ceramologists of the ArAr laboratory. The ethnographic description of the 2cm space between the bellows tubes and the tuyères could also be a key feature for controlling the rate of air intake to regulate temperature and reaction speed inside the furnace [START_REF] Rehder | The Mastery and Uses of Fire in Antiquity[END_REF]. Inside the furnace, the most immediate change is to increase the slope at the base of the furnace to facilitate evacuation of the slag. The fuel-to-ore ratio (2:1) suggested from the ethnographic data is undoubtedly one of the main reasons for the high-carbon content alloy produced in this experiment. This ratio is therefore extremely important when reducing iron-rich ores, and would be critical when attempting to smelt the eastern iron reserves from Phnom Dek. Again, the cast iron produced in our furnace is linked to our inability to control the rate of air intake (i.e., creating very high temperatures) which was exacerbated by the large number of tuyères. These factors all need to be considered in order to produce the low-carbon blooms typical of the late Angkor period.

7.2 Chemical relationships between ore, slag and bloom for provenance attempts The NRC ratios measured in ore, smelting slag and slag into pieces of bloom were compared to identify patterns within the experimental smelting system (Figure 12). As expected, the ratios for the slag (tap, furnace, bloom) are different from the ores. These results are in accordance with the fact that the chemical signatures in the slag is strongly constrained by the furnace material and the fuel ash composition. The signatures based on major elements are therefore related to the smelting process itself [START_REF] Buchwald | Slag analysis as a method for the characterization and provenancing of ancient iron objects[END_REF][START_REF] Paynter | Regional variations in bloomery smelting slag of the iron age and romano-british periods[END_REF][START_REF] Dillmann | Slag inclusion analyses for studying ferrous alloys employed in French medieval buildings: supply of materials and diffusion of smelting processes[END_REF][START_REF] Blakelock | Slag inclusions in iron objects and the quest for provenance: an experiment and a case study[END_REF][START_REF] Charlton | Investigating the production provenance of iron artifacts with multivariate methods[END_REF] rather than a provenance to a geological ore. Differences are also evident between the two types of slag with the elemental ratios for tap slag being relatively constant in comparison to the more heterogeneous furnace slags. The diversity within the latter type relates to their formation relative to their placement within the furnace and the varying contributions of proximal parent materials. This result is a key reminder of the importance of using tap slag in attempts to identify the provenance of iron products. Ratios for the large data set collected from the bloom are also quite scattered. Slight compositional differences are discernible between the main body of data from the bloom and the tap slag, especially those including CaO, Al2O3 and MgO. The compositional heterogeneity seen here could be a consequence of bloom mass formation at different places within the furnace structure. Such variability complicates direct correlations between tap slag and bloom and may considerably limit the use of major elements in assessing provenance to a smelting process. As already suggested for other contexts [START_REF] Blakelock | Slag inclusions in iron objects and the quest for provenance: an experiment and a case study[END_REF], it is fundamental to consider that variable furnace material contributions to the slag could result in chemical overlaps that dilute any specific signature even for different production provenances. Ongoing analyses of these samples will permit to compare and test the consistency of trace elements for defining less-scattered signatures and test relationships throughout this experimental assemblage for provenancing attempts [START_REF] Coustures | The use of trace element analysis of entrapped slag inclusions to establish ore -Bar iron links: examples from two Gallo-Roman iron-making sites in France (Les Martys, Montagne noire, and les Ferrys, Loiret)[END_REF][START_REF] Desaulty | Does it come from the Pays de Bray? Examination of an origin hypothesis for the ferrous reinforcements used in French medieval churches using major and trace element analyses[END_REF]Leroy et al., 2012).

Table 3: Radiocarbon dating results for the charcoal pieces and the iron samples. Calibration was performed with OxCal 4.3.2 [START_REF] Ramsey | Methods for Summarizing Radiocarbon Datasets[END_REF]; r:0.02; Post-bomb atmospheric NH3 curve [START_REF] Hua | Atmospheric Radiocarbon for the Period 1950-2010[END_REF]; Post-bomb atmospheric curve [START_REF] Levin | Atmospheric Δ14CO2 trend in Western European background air from 2000 to[END_REF][START_REF] Hammer | Monthly mean atmospheric D14CO2 at Jungfraujoch and Schauinsland from 1986 to[END_REF].

Sample

Conclusions and Perspectives

This initial experimental smelt was designed to address some technical questions relative to the construction of furnaces and the metallurgical process employed during the late Angkor period. The end result, perhaps unsurprisingly, failed to produce comparable quantities and qualities of slag and iron as seen in the archaeological systems around Phnom Dek. However, valuable information was obtained for future tests including changes to the composition, placement and inclination of the tuyères, the ratios of raw materials, limit of fuel size and a reorganization of the air supply system to allow better temperature management necessary to produce a low-carbon bloom. Our analysis of the waste and products of the smelt also provided useful insights into chemical variability and iron dating of an unprocessed iron bloom.

The results confirm that direct correlation between iron product and slag using only major elements may be much more complex and should be confirmed with a larger data set and complemented with other scales of analysis. On-going study of trace elements from this experiment will continue to refine our understanding of this smelting system and, more broadly, to confirm the chemical relationship between ore, slag and object for provenance studies. Our results also demonstrate that iron alloys are viable artifacts for direct dating and confirm the reliability of previous dates obtained from crampons recovered from Angkor period temples [START_REF] Leroy | The ties that bind: archaeometallurgical typology of architectural crampons as a method for reconstructing the iron economy of Angkor, Cambodia[END_REF]S. Leroy et al., 2015a). In the near future, the charcoal species identification from archaeological sites would help significantly to select the adequate fuel in order to better approximate the 14C content in the furnace. Finally, we hope that the experimental work conducted at the EFEO in Siem Reap will encourage local and international scholars to continue the reconstruction and preservation of Angkorian heritage beyond its elaborate temple complexes. This experiment has provided a public display and publication in Khmer [START_REF] Tauch | expérimenté de la réduction du fer de l'ecole française d'extrême-orient[END_REF]. Future attempts to smelt iron -and fire ceramics -will benefit from this dissemination of results and the integration of new technological details recovered from excavation and survey. The results of these collaborative activities in turn provide essential information for archaeological and archaeometric researches and, more specifically, the role of pyrotechnologies within the historical trajectory of premodern Cambodia.

Figure 2 :

 2 Figure 2: Examples of tap slag found on Angkorian archaeological sites from the Phnom Dek area.

Figure 3 :

 3 Figure 3: Base of the furnace with tapping pit and key features of the structure.

Figure 4 :

 4 Figure 4: The smelting process and the Kuay furnace. (Top) Illustration "Fonderie de fer chez les Kouys" (Boulangier, 1888). (Bottom) Photo of the remains of a Kuay furnace in Rumchek (1969) (courtesy B.Dupaigne). Remaining wood walls from the air supply system exhibit the numerous holes for the air supply.

5

  Two tons (2000 kg) of the two varieties of iron ores found at Phnom Dek were collected in 2018 for this 6 experiment. A mix of both varieties (ca. 50%/50%) was used to ensure sufficient quantities of gangue and 7 to create slag. All ores were roasted in an open fire and crushed into 2 to 3 cm pieces prior to smelting. 8 9

Figure 7 :

 7 Figure 7: Temperatures reached at the thermocouples (T1, T2) during the smelting. (a) Blower start-up. (b) 1 st charge of ore (6 kg). (c) Quantity of ore charge reduced to 4 kg. (d) Quantity of charcoal charge reduced to 6 kg. (e) Temperature decrease: opening of the front hole to flow the slag. (f) Unsuccessful attempt to unclog the tuyère.Table 2: Quantity of parent materials (charcoal, ore), iron and slag produced.

Figure 11 :

 11 Figure 11: Optical microscopy for experimental tap slag (A and B) and furnace slag (C). (A): Welldeveloped fayalitic laths. (B) Fayalitic laths and fine wüstite dendrites. (C) Example of partially reducedore fragment. Overall, the thermochemical profile of the furnace, slag characteristics, and bloom-slag separation clearly show that the experiment is not yet representative of the Angkorian smelting process. The technical choices made by the authors unsurprisingly hindered the final outcome but also provide clues about where changes need to be effected. Most obvious is that several aspects of the air delivery system were inadequate. Tuyères that failed to melt during the operation quickly became partially blocked by the accumulation of slag at the bottom of the furnace. This points to both an incorrect tuyère inclination and clay composition used to make them. Following some ethnographic accounts, the inclination and placement of the tuyères should arrive at the mid-height of the walls relative to the outside of the furnace. A tuyère and wall fragment recovered from Sanlong Jaya, a 20 th c. Kuay smelting site near Phnom Dek[START_REF] Pryce | The Iron Kuay of Cambodia: tracing the role of peripheral populations in Angkorian to colonial Cambodia via a 1200 year old industrial landscape[END_REF] may indicate the use of a 45° angle for the tuyères. This new positioning combined with a decreased ratio of sand in the clay, or a different nature of the clay, would allow the tuyères to melt without collapsing on themselves and reduce their size as the metal mass grows inside the furnace. This

Table 1 :

 1 Comparison of archaeological and ethnographic features, and experimental choices 1

	Data sources	Tuyères	Furnace design	Air supply mechanism
	Archaeological evidence	Type: Medium-gauge (cm) (2.3<ID<3 ;4.5<ED<6)
	(13th c.-14th c.)	Number on each wall: unknown

Table 2 :

 2 Quantity of parent materials (charcoal, ore), iron and slag produced.

	Parent materials (kg)	Products and slag (kg)
	Charcoal (heating)	66	Raw iron mass	29.8 (ore/bloom=3.35)
	Total Charcoal	242	Tap slag	2
			Furnace slag	18.8
	Ore	100	Slag accumulated around the tuyères	16

Acknowledgments

Funding for this project was provided by the French National Research Agency (ANR-14-CE31-0007)

Radiocarbon dating analyses

Six charcoal samples were selected for 14 C measurements including two from the internal and external part of a carbonised log (6 cm diameter), two samples from furnace slags, one adhering to the metallic Mass 1 and one from inside the furnace after the smelt. Three samples of metal were extracted from Mass 1 and from a smaller metal piece. All the results show two dating intervals (Table 3). The first range is between 1957 and 1962 and correspond to the fast rising of the 14 C content in the atmosphere caused by atmospheric nuclear detonations. The second range conform to the decreased 14 C content from 1965 onwards (Figure 13). Considering the large diameter of some logs used for the experimental smelt, the oldest interval cannot be systematically discarded for the dates on charcoal. Nevertheless, we can reasonably assume that the majority of charcoal pieces introduced in the furnace are posterior to this interval, with some of them ranging from the eighties (SacA 59795: 1981-1983 AD) until the present (SacA 59798: 2009-2013 AD). Unlike the charcoals that all give different radiocarbon dates, the three iron samples show close 14 C contents corresponding to an interval of calibrated dates from 1999 to 2003 AD. The strong similarity of the 14 C results of the iron samples reflects a homogeneous 14 C content in the reducing CO when diffusing into the metal being formed. It demonstrates that iron alloy records the global 14 C activity of the wood charcoal used as fuel. Considering the old dates obtained for some charcoal fragments, a reasonable age offset of 15 to 19 years relative to the date of the experiment is obtained for the metal. This result shows that the old wood effect often attributed to iron 14 C dating must not be overemphasised and is probably even lower in most cases where the fuel is selected from small trunks and young branches. Furthermore, our experiment shows that iron alloys can be a more reliable dating artefact compared to small unselected charcoals possibly coming from the oldest parts of the wood fuel loaded in the smelting furnace. and the National Science Foundation Senior Research Grant (1550850). We are grateful to people who help in the research design: Caroline Rufino (event organization and communication), Olivier Le Tétour (ventilation construction), Lounh Leap (site manager who helps for the construction of the furnace), Javier Sánchez-Monge Escardo (photo coverage). The authors acknowledge the LAPA-IRAMAT-NIMBE staff for access to the laboratory facilities and ARTEMIS staff for sample preparation and AMS operating. The LMC14 is funded by five French organizations: CEA, CNRS, IRD, IRSN, and the Ministry of Culture (France). Access to the iron ores from Phnom Dek was provided by the Ministry of Culture and Fine Arts of Cambodia. Since 2014, the EFEO center in Siem Reap/Angkor has sponsored workshops devoted to experimental archaeology. For several years, experiments dedicated to the study of Khmer stoneware production have been carried out in collaboration with the Cerangkor program (dir. A. Desbat, CNRS). Finally, our thanks go to the two referees for all their helpful suggestions and comments.

CRediT authorship contribution statement


Maxime Adloff
email: pro.maximeadloff@gmail.com

Sylvie Maurice

Bernard Paternostre

Thierry Vimard

Infirmiers libéraux : premiers acteurs des soins palliatifs en phase avancée et terminale à domicile Private practice nurses: major actors of home palliative care for patients with advanced and end-stage disease

Introduction

Le droit de finir sa vie et de mourir chez soi, inscrit dans la loi depuis 1999, est aujourd'hui un enjeu de santé publique à la croisée d'une demande de la population, et des contraintes du système de santé [START_REF]Loi n o 99-477 du 9 juin 1999 visant à garantir le droit à l'accès aux soins palliatifs[END_REF][START_REF] Anon | Fin d'un tabou ! La mort, la fin de vie[END_REF][START_REF] Duhamel | Les soins palliatifs et la fin de vie à domicile[END_REF]. Ce changement de modèle intervient dans un contexte sociodémographique, socioéconomique et sanitaire particulier : le vieillissement de la population française, engendré par l'allongement de l'espérance de vie et l'arrivée à l'âge de la retraite de la génération des « baby-boomers » (4). Sur le plan sanitaire, les conséquences de ce vieillissement sont marquées par une augmentation de la prévalence des maladies chroniques létales et des polypathologies. Il est estimé que le taux de mortalité par an, toutes causes confondues augmentera de 25 % par an d'ici 2050 [START_REF] Blanpain | Projections de population 2007-2060 pour la France métropolitaine[END_REF]. Le nombre de situations palliatives croîtra parallèlement puisque 62 % des décès relèveraient de soins palliatifs [START_REF] Ravanello | L'Atlas des soins palliatifs et de la fin de vie en France : Première édition[END_REF].

Les situations palliatives avancées et terminales représentent l'évolution inéluctable de pathologies non guérissables, où les priorités sont le soulagement des symptômes, le confort de vie du malade, et l'accompagnement des proches [START_REF] Hirsch | Réponses et commentaires concernant le QRM 3 : soins palliatifs et trajectoires de vie des patients[END_REF]. Les situations palliatives avancées ou symptomatiques, dont le pronostic se compte généralement en semaines voire en mois, sont distinguées des situations palliatives terminales où le décès est imminent.

Ce problème sociétal appelle à l'anticipation et rend nécessaire la réflexion sur les missions et la place des acteurs concernés par les soins palliatifs à domicile. La question de l'organisation de l'offre de soin est donc centrale dans le virage ambulatoire et de la prise en charge à domicile qui s'opère.

Actuellement, les pouvoirs publics orientent en priorité l'offre de soins vers l'hospitalisation à domicile dont la place est prépondérante dans le plan 2015-2018 pour le développement des soins palliatifs [START_REF] Anon | Plan national 2015-2018 pour le développement des soins palliatifs et l'accompagnement en fin de vie[END_REF]. D'autres acteurs infirmiers concourent aux soins palliatifs à domicile, notamment les infirmiers libéraux. Leur activité bénéficie cependant d'une faible visibilité et de peu de soutien de l'assurance maladie en termes de dispositifs conventionnels [START_REF] Anon | Vivre la fin de sa vie chez soi[END_REF][START_REF] Anon | Les soins palliatifs : une prise en charge toujours très incomplète[END_REF]. Par ailleurs, leur degré d'implication dans les situations palliatives à domicile n'est pas connu. Les états des lieux nationaux de 2008 et de 2017 mentionnent le manque de données issues des prises en charge à domicile, a fortiori dans le secteur libéral [START_REF] Duhamel | Les soins palliatifs et la fin de vie à domicile[END_REF][START_REF] Cabé | Rapport sur l'état des lieux du dispositif de soins palliatifs au niveau national[END_REF]. Ces données seraient pourtant nécessaires au pilotage de l'offre de soins. L'objectif de ce travail était de décrire la place respective des différents acteurs de soins infirmiers dans les situations palliatives avancées et terminales à domicile. Les médecins traitants ont été interrogés parce qu'ils sont les prescripteurs des soins infirmiers, et qu'ils peuvent identifier les situations palliatives. Les variables d'intérêt étaient les modalités d'exercice des infirmiers intervenant au domicile des patients : libéraux, en centre de soins infirmiers, en service de soins infirmiers à domicile, en hospitalisation à domicile, ainsi que les collaborations de ces acteurs.

Matériel et méthode

Les données ont été collectées sur la plateforme « Limewire ® », organisées en base de données sur « Excel ® ». Les analyses descriptives ont été réalisées avec « EpiInfo 7 ® ».

Résultats

En tout, 89 médecins ont participé à l'étude en complétant en ligne tous les items du questionnaire, parmi les 134 qui s'étaient connectés à la plateforme. Ils étaient autant de sexe féminin que masculin (46 contre 43). Les femmes étaient plus jeunes que les hommes : 65 % d'entre elles avaient moins de 50 ans contre 42% des hommes. Les médecins exerçaient davantage en milieu urbain que rural (52 contre 37). collaboration avec des infirmiers libéraux ou des services d' hospitalisation à domicile dans 11% des situations décrites.

Discussion

Le choix a été fait de recueillir les données auprès des médecins traitants qui sont les prescripteurs des soins infirmiers, qui centralisent l'information et sont en mesure d'identifier les situations palliatives avancées et terminales ; et enfin parce qu'il n'existe pas à l'heure actuelle de base de données pour les soins palliatifs à domicile. Cela a sans doute entraîné un biais de sélection, lié à une possible sensibilisation aux soins palliatifs des médecins répondants. Cependant, la place des différents acteurs de soins infirmiers, qui représente l'objectif principal de cette étude, dépend de nombreux autres facteurs.

La méthodologie rétrospective de l'enquête par questionnaire entraîne généralement un biais de mémorisation. Il a probablement été atténué ici par le caractère grave et marquant pour les médecins des situations palliatives et des décès ; et par l'utilisation des indicateurs de l'outil SPICT-FR™ pour classer les patients dans les différents groupes de pathologies et aider les médecins à se rappeler des situations.

En ce qui concerne le biais de classement des patients et des soignants, du fait de la nature déclarative du recueil de données il n'était pas possible d'effectuer de vérifications. Cependant, les médecins rencontrés lors de l'enquête préliminaire n'avaient exprimé de difficultés, ni dans le repérage des patients en situations palliatives, tous les items de l'outil SPICT-FR™ leur semblant clairs, ni pour se rappeler des infirmiers impliqués dans les soins prescrits à domicile.

En revanche, le questionnaire ne permettant pas l'évaluation de la singularité et de la complexité propre à chaque situation, il n'était pas possible de connaître l'adéquation des ressources employées aux besoins nécessaires, ni la qualité des soins et la satisfaction des acteurs et des patients. Rappelons que l'objectif principal était de décrire avec précision la place respective des différents acteurs infirmiers impliqués actuellement sur le territoire dans les soins palliatifs à domicile, en faisant l'hypothèse que les médecins seraient de bons « informateurs ». Le grand nombre de médecins répondants et de situations décrites a permis d'atteindre cet objectif.

Les réponses à l'enquête, par 89 médecins exerçant sur un territoire urbain et rural, ont montré que les infirmiers libéraux ont une place prépondérante dans les soins palliatifs à domicile. Les infirmiers libéraux assurent seuls la prise en charge de 64% des patients en situations palliatives avancées et terminales en cours de suivi ; et la prise en charge de 56% des patients dans le mois précédant leur décès. Ils interviennent également en collaboration avec les services de soins infirmiers et d'hospitalisation à domicile et dans la majorité des situations où ces structures sont présentes.

En ce qui concerne la place prépondérante des infirmiers libéraux dans les soins palliatifs à domicile, seuls ou avec les services de soins infirmiers et d'hospitalisation à domicile, nous n'avons pas trouvé dans la littérature, d'étude avec laquelle mettre en perspective ces résultats, comme le rapportait l'Inspection générale des affaires sociales en 2017 (3). Cependant ceux-ci nuancent et interrogent la vision souvent partagée que la majorité des prises en charge en soins palliatifs à domicile serait réalisée par les structures d' hospitalisation à domicile [START_REF] Hirsch | Réponses et commentaires concernant le QRM 3 : soins palliatifs et trajectoires de vie des patients[END_REF].

Les résultats par pathologie confirment que les services d' hospitalisation à domicile ont une activité centrée sur l'oncologie (25 % des prises en charge dans ce groupe versus moins de 10 % dans tous les autres groupes pathologiques). Ce résultat est concordant avec les statistiques nationales qui montrent que plus d'un tiers de l'activité des structures d' hospitalisation à domicile concernent des pathologies cancéreuses [START_REF] Cabé | Rapport sur l'état des lieux du dispositif de soins palliatifs au niveau national[END_REF]. Quant aux services de soins infirmiers à domicile dont la mission principale est le maintien de l'autonomie des personnes âgées, ils sont présents dans tous les groupes de pathologies avec, logiquement, une activité plus importante, à hauteur de 25 % des prises en charge des maladies neurologiques et des démences/fragilité. Enfin, le nombre moyen de dix et la médiane de huit situations palliatives avancées et terminales suivies à domicile par médecin en une année peuvent sembler importants à côté du chiffre de un à trois habituellement rencontré dans la littérature [START_REF] Anon | Plan national 2015-2018 pour le développement des soins palliatifs et l'accompagnement en fin de vie[END_REF]. Cela peut être le reflet de l'intérêt particulier des médecins de l'échantillon pour les soins palliatifs, et donc d'un exercice incluant cette pratique. Mais il peut aussi provenir d'une meilleure identification des situations palliatives grâce au recours à un outil de repérage. Les résultats de l'enquête préliminaire allaient déjà dans ce sens, puisque les médecins relevaient davantage de situations avec le SPICT™ que sans outil.

Conclusion

Cette étude montre que les infirmiers libéraux, dont le degré d'implication dans les soins palliatifs à domicile n'était pas pleinement identifié, effectuent la majorité des soins infirmiers prescrits par les médecins traitants dans les situations palliatives avancées et terminales. Ils interviennent essentiellement seuls au domicile des malades et leurs compétences sont aussi très souvent sollicitées par les services de soins infirmiers à domicile et les structures d' hospitalisation à domicile. Dans l'organisation des soins palliatifs à domicile, ils sont des acteurs incontournables de l'offre de soin. Le développement des soins palliatifs à domicile et de la culture palliative passera par une meilleure reconnaissance et le soutien de ces acteurs.

Cette étude a également permis d'estimer à dix en moyenne le nombre de patients en situations palliatives avancées et terminales que prenaient en charge à domicile les médecins généralistes de Gironde. Elle a aussi permis de montrer que l'outil d'identification SPICT-FR™, dont la diffusion en médecine générale n'est pas connue, s'était avéré utilisable par un grand nombre de médecins pour repérer les patients en situations palliatives avancées et terminales.

Par ailleurs, il n'existe pas de données à l'échelle nationale pour décrire l'ampleur de la prise en charge en soins palliatifs à domicile par les médecins traitants et les infirmiers libéraux. S'il existait par exemple une « ALD soins palliatifs » il serait possible d'identifier voire de valoriser la prise en charge de ces patients en dehors de l'hôpital. Les critères restent à définir en s'inspirant d'outils validés (indices de Karnofski, de l'OMS, PPS, SPICT-FR™, Pallia 10, etc.) et en incluant l'expérience des professionnels de médecine générale et des soins palliatifs.

Enfin, d'autres études pourraient être conduites auprès des acteurs infirmiers pour identifier les patients et connaitre l'adéquation des ressources employées aux besoins en soins nécessaires dans les phases avancées et terminales des situations palliatives à domicile.

Annexe 1

Questionnaire de l'étude.

Annexe 2

Version française du Supportive & Palliative Care Indicators Tool (SPICT-FR™) : indicateurs cliniques d'une ou plusieurs maladies limitant l'espérance de vie.

Liens d'intérêts

Les auteurs déclarent n'avoir aucun lien d'intérêts.

Financement

Cette recherche n'a bénéficié d'aucune subvention spécifique émanant d'organismes de financement publics, commerciaux ou à but non lucratif.

Légendes des figures

  Les patients en cours de suivi étaient décrits selon les sept catégories pathologiques définies par le Supportive & Palliative Care Indicators Tool dans sa version française (SPICT-FR™) (Annexe 2) : cancer, maladie cardiovasculaire, maladie respiratoire, maladie rénale, maladie hépatique, maladie neurologique et démence/fragilité[START_REF] Highet | Development and evaluation of the Supportive and Palliative Care Indicators Tool (SPICT): a mixed-methods study[END_REF]. Pour chaque catégorie, les indicateurs cliniques spécifiques étaient présentés aux médecins. Le choix d'un outil d'identification, le SPICT-FR™, avait pour but de faciliter le repérage des situations palliatives avancées et terminales, et de permettre une classification en catégories de pathologies afin d'effectuer des analyses en sous-groupes. Cet outil est également recommandé par la Haute autorité de santé[START_REF] Anon | Comment favoriser le maintien à domicile des patients adultes relevant de soins palliatifs ? Saint-Denis La Plaine : Haute autorité de santé[END_REF].Pour les patients décédés, la pathologie n'était pas décrite. Le domicile était défini comme le domicile privé des patients et excluait les patients vivant en établissement d'hébergement pour personnes âgées dépendantes et dans les autres établissements médicosociaux. Enfin il était demandé aux médecins de renseigner des données sociodémographiques, et leur formation en soins palliatifs.

Figure 1 .

 1 Figure 1. Étude sur la place respective des différents acteurs de soins infirmiers dans les situations palliatives avancées et terminales à domicile : distribution des médecins répondants à l'enquête en fonction du nombre de patients suivis en situations palliatives avancées et terminales, ou décédés, dans l'année (n= 89).

Figure 2 .

 2 Figure 2. Étude sur la place respective des différents acteurs de soins infirmiers dans les situations palliatives avancées et terminales à domicile : répartition des patients en cours de suivi ou décédés pendant les 12 derniers mois, en situations palliatives avancées et terminales selon les soignants à domicile. HAD : hospitalisation à domicile ; IDE : infirmier diplômé d'état ; SSIAD : service de soins infirmiers à domicile.

Figure 3 .

 3 Figure 3. Étude sur la place respective des différents acteurs de soins infirmiers dans les situations palliatives avancées et terminales à domicile : répartition des patients en situation palliative avancée et terminale en cours de suivi selon la pathologie et les soignants à domicile (n=607). HAD : hospitalisation à domicile ; IDE : infirmier diplômé d'état ; SSIAD : service de soins infirmiers à domicile.

  infirmier Service de soins infirmiers à domicile Coordination IDE/SSIAD Hospitalisation à domicile Coordination IDE/HAD Coordination SSIAD/HAD Pas de soignant Données manquantes

  Cette étude descriptive, transversale et rétrospective, correspond à une enquête de pratique. Une enquête préalable réalisée auprès de huit médecins généralistes avait permis de créer un questionnaire standardisé et compréhensible. Pour l'étude, tous les médecins généralistes de Gironde, installés, et inscrits au tableau de l'ordre des médecins du département ont été sollicités, soit 1541 médecins. Ils ont été contactés par courriel à deux reprises, les 4 juillet et 23 septembre 2019 et invités à répondre à un questionnaire anonyme en ligne. La fin du recueil de données était fixée au 8 octobre 2019.

	Le questionnaire portait d'une part sur l'identification des patients en situations palliatives
	avancées et terminales en cours de suivi et des patients décédés à domicile pendant les 12 derniers
	mois à l'issue d'une pathologie en situation palliative (Annexe 1). Il portait, d'autre part, sur
	l'identification des infirmiers (et/ou des structures) qui réalisaient les soins à domicile auprès de
	chaque patient décrit. Pour les patients décédés, il était demandé d'identifier les infirmiers, les
	structures, les coordinations ou les relais entre acteurs, le mois précédant le décès.

en une année, en faisant la somme des patients en cours de suivi et des patients décédés pendant les 12 derniers mois. Dans cet échantillon le 25 e percentile et la médiane étaient respectivement de cinq et huit patients suivis (Fig 1) . Ils ont décrit la prise en charge de 607 patients en situations palliatives avancées et terminales en cours de suivi et de 260 patients décédés à domicile au cours des 12 derniers mois (Fig 2).En ce qui concerne les situations palliatives en cours de suivi, les soins infirmiers ont été réalisés en majorité par des infirmiers libéraux. Ils ont assuré, seuls, 64% de l'ensemble des prises en charge. Les autres soins infirmiers ont été réalisés par les service de soins infirmiers à domicile dans 16% de l'ensemble des situations, l' hospitalisation à domicile dans 9%, et les centre de soins infirmiers dans 3%. L'intervention des service de soins infirmiers à domicile et d' hospitalisation à domicile était en majorité effectuée en collaboration avec des infirmiers libéraux : ces derniers ont participé à 60% des prises en charge avec les service de soins infirmiers à domicile, et à 56% des prises en charge avec ceux de l' hospitalisation à domicile. L'intervention conjointe des service de soins infirmiers/hospitalisation à domicile était rare. En cumulant leurs interventions, seuls et cordonnées aux structures, les infirmiers libéraux étaient présents dans 78% des situations palliatives avancées et terminales en cours de suivi. Les médecins ont déclaré que 35 patients, soit 6%, n'avaient pas d'infirmier à domicile, et n'ont pas renseigné l'infirmier intervenant pour moins de 3% des patients. L'analyse des prises en charge selon les pathologies définies par le SPICT-FR™ montre que les infirmiers libéraux ont assuré seuls plus de 50% des prises en charge dans six des sept catégories de pathologies (Fig 3). Les structures d' hospitalisation à domicile intervenaient essentiellement pour des pathologies oncologiques où leur activité représentait 25 % des prises en charge et moins de 10 % dans les autres groupes de pathologies. Les services d'hospitalisation à domicile étaient absents dans la prise en charge des pathologies cardiovasculaires et des démences/fragilité. Les service de soins infirmiers à domicile étaient présents dans la prise en charge de toutes les pathologies, mais leur activité était plus marquée, à hauteur de 25 %, pour les maladies neurologiques et les démences/fragilité. En ce qui concerne les patients décédés, les infirmiers libéraux ont réalisé, seuls, 56 % des prises en charge le mois précédant le décès (Fig 2). En cumulant leurs interventions seuls et coordonnées aux structures, les infirmiers libéraux étaient présents le mois précédant le décès dans 76% des situations décrites. Les structures d' hospitalisation à domicile intervenaient seules ou de manière coordonnée avec les infirmiers ou les service de soins infirmiers à domicile, ou en relais, dans 25% des situations déclarées. Les services de soins infirmiers à domicile intervenaient seuls ou en