Stephan Soler

Christine Montout

Mocrane Abbar

Thibault Mura

Jorge López-Castroman

Impact of cannabis use on outcomes of patients admitted to an involuntary psychiatric unit: a retrospective cohort study

Introduction

Cannabis is the most widely-used illegal substance in the world. Consumption has increased in recent years globally, and about 188 million people used the drug in 2017 (World Drug Report 2019). In France, recent surveys showed that during their lifetime 44.8% of adults (18 to 64 years old) and nearly four in ten adolescents before 18 had tried cannabis at least once (OFDT, 2017;OFDT, 2018). Although cannabis is not socially perceived to be a high-risk drug [START_REF] Hughes | Marijuana use and perceived risk of harm from marijuana use varies within and across states[END_REF], cannabis use is a risk factor for several mental disorders, including psychotic disorders and mood disorders [START_REF] Gobbi | Association of Cannabis Use in Adolescence and Risk of Depression, Anxiety, and Suicidality in Young Adulthood: A Systematic Review and Meta-analysis[END_REF][START_REF] Hall | Cannabis use and the risk of developing a psychotic disorder[END_REF][START_REF] Kiburi | Cannabis use in adolescence and risk of psychosis: Are there factors that moderate this relationship? A systematic review and meta-analysis[END_REF] and is associated with psychiatric hospitalizations [START_REF] Lai | Exploration of the comorbidity of cannabis use disorders and mental health disorders among inpatients presenting to all hospitals in New South Wales, Australia[END_REF][START_REF] Prince | Risk of inpatient stay for mental illness among individuals with substance use disorders[END_REF]. The mechanisms connecting cannabis to these outcomes remain unclear [START_REF] Hamilton | Are we any closer to identifying a causal relationship between cannabis and psychosis?[END_REF].

For many years, the literature has highlighted the association between cannabis use and psychotic symptoms, such as a delusional states, hallucinations and emotional lability (W. [START_REF] Hall | Cannabis use and psychosis: A review of clinical and epidemiological evidence[END_REF][START_REF] Cleghorn | Substance abuse and schizophrenia: Effect on symptoms but not on neurocognitive function[END_REF] or psychotic disorders [START_REF] Lai | Exploration of the comorbidity of cannabis use disorders and mental health disorders among inpatients presenting to all hospitals in New South Wales, Australia[END_REF][START_REF] Schimmelmann | Prevalence and impact of cannabis use disorders in adolescents with early onset first episode psychosis[END_REF][START_REF] Ksir | Cannabis and Psychosis: A Critical Overview of the Relationship[END_REF][START_REF] Singh | A review of Indian research on co-occurring cannabis use disorders& psychiatric disorders[END_REF]. The relative risk of developing psychosis among cannabis users is estimated to be 2:1 for occasional use and 6:1 for heavy users [START_REF] Bagot | Adolescent Initiation of Cannabis Use and Early-Onset Psychosis[END_REF][START_REF] Di Forti | Proportion of patients in south London with first-episode psychosis attributable to use of high potency cannabis: A case-control study[END_REF]. Several outcomes of cannabis use in terms of psychosis have been described: i) self-limited psychotic symptoms during acute intoxications; ii) brief psychotic episodes, immediately after the intoxication; and iii) the emergence of persistent psychotic symptoms later in life, an outcome that seems to be associated particularly with early, frequent and heavy use in adolescence [START_REF] Kiburi | Cannabis use in adolescence and risk of psychosis: Are there factors that moderate this relationship? A systematic review and meta-analysis[END_REF][START_REF] Rubino | Adolescent exposure to cannabis as a risk factor for psychiatric disorders[END_REF][START_REF] Rylander | The association of cannabis use on inpatient psychiatric hospital outcomes[END_REF]. Importantly, in about half of the cases cannabis-induced psychosis converts to schizophrenia in the next few years [START_REF] Starzer | Rates and Predictors of Conversion to Schizophrenia or Bipolar Disorder Following Substance-Induced Psychosis[END_REF].

Another study estimated that people who abuse cannabis have three times more risk of being hospitalized for psychiatric disorders [START_REF] Prince | Risk of inpatient stay for mental illness among individuals with substance use disorders[END_REF]. This risk is also increased (odds ratio of 6) as a function of the dose consumed [START_REF] Schubart | Association between cannabis and psychiatric hospitalization[END_REF]. Consistently, cannabis use has been found to increase relapse rates, predispose to more hospitalizations, increase positive symptoms and increase suicidality in patients with schizophrenia [START_REF] Østergaard | Associations between substance use disorders and suicide or suicide attempts in people with mental illness: A Danish nation-wide, prospective, register-based study of patients diagnosed with schizophrenia, bipolar disorder, unipolar depression or personality disorder[END_REF][START_REF] Prince | Risk of inpatient stay for mental illness among individuals with substance use disorders[END_REF][START_REF] Rozin | A retrospective study of the role of long-acting injectable antipsychotics in preventing rehospitalization in early psychosis with cannabis use[END_REF][START_REF] Schoeler | Poor medication adherence and risk of relapse associated with continued cannabis use in patients with first-episode psychosis: A prospective analysis[END_REF]. Patients admitted in involuntary units seem to be more likely to have substance use disorders, including cannabis, compared with patients in other psychiatric units [START_REF] Hustoft | Predictors of involuntary hospitalizations to acute psychiatry[END_REF]. According to the results of a Spanish study in a small sample, patients who used cannabis after an involuntary admission for a first psychotic episode had more problems of adherence to treatment [START_REF] Barbeito | Cannabis use and involuntary admission may mediate long-term adherence in first-episode psychosis patients: A prospective longitudinal study[END_REF]. Once the psychotic episode is over, cannabis use may increase the risk of relapse [START_REF] San | Factors associated with relapse in patients with schizophrenia[END_REF][START_REF] Bergé | Predictors of Relapse and Functioning in First-Episode Psychosis: A Two-Year Follow-Up Study[END_REF]. However, the relationship between cannabis use and resistance to treatment has not been sufficiently studied [START_REF] Legge | Clinical indicators of treatment-resistant psychosis[END_REF].

The use of cannabis plays an important role in the development of psychotic disorders, relapse, and the number of psychiatric hospitalizations. In some cases, the severity of the symptoms can lead to forced hospitalizations. Our goal is to compare the clinical profile of cannabis users and non-users according to the urinary screening at admission in a secure unit for involuntary care. We hypothesize an impact of cannabis use on the number of hospitalizations, the length of hospital stays and the use of antipsychotics in this population.

Materials and methods

Population:

The study was conducted in a secured psychiatric intensive care unit with a capacity of 30 beds between January 1, 2016 and December 31, 2016. The total sample includes 370 involuntarily hospitalized patients (under request of a third party or a representative of the state) according to the terms of the law of 04 July 2011. Criteria for involuntary admission in France include the following: i) the person suffers a mental disorder, ii) the mental disorder renders the person incapable of giving consent, and iii) the person's mental state requires immediate care with constant monitoring (LOI N° 2011(LOI N° -803, 2011)).

All patients who were hospitalized in the unit for the first time in 2016 were included.

No exclusion criteria were applied since 1) we aim to reflect the reality of involuntary care, and 2) the retrospective nature of the study prevented a clinical assessment during which exclusion criteria could have been applied.

Only readmissions to the same unit were considered since it is the only involuntary unit in the catchment area. We did not take into account hospitalizations in other hospitals or non-involuntary units. In France, psychiatric care is organized in general psychiatry sectors providing care for about 70 000 adult patients each. Forced admissions are made only in public hospitals within those sectors. With the exception of homeless patients or a change of address, patients involved in our study would have been transferred to our unit in case of involuntary admission in another sector of care.

Tetrahydrocannabinol measurement:

All patients entering the unit were routinely screened for illegal drugs using a urinary test at the moment of admission that detected tetrahydrocannabinol (THC). The patients were accompanied during the urine collection to avoid potential distortions in the results. The presence of 11-nor-Δ9 THC-9-carboxylic acid (Δ9 COOH-THC) was detected using the Cannabinoid II (THC2) assay (Roche) according to the manufacturer's instructions and analyzed on the Roche / Hitachi Cobas C system. The time from admission until urine drug testing was recorded for each patient.

Collection of socio-demographic and diagnostic data:

All data used in this study was obtained retrospectively from patient clinical records with authorization of the CNIL (Commission Nationale de l'Informatique et des Libertés) and Institutional Review Board (N°19.10.06). Participants were not interviewed or assessed with regards to this study. Following advice from the Institutional Review Board, informed consent was waived because of the retrospective nature of the study and the low risk for participants. During the course of the study, a poster was displayed within the unit to inform patients that a study was underway and to invite them to contact a physician for further information or to oppose their inclusion.

Age, sex, family and work status, were collected at the time of the patient interview for clinical purposes. The duration of hospitalization, the number of readmissions and the medical diagnoses were recorded.

Marital status was regrouped into single (single, divorced or separated) and in a relationship (including married and couples living together). Occupational situation was regrouped into inactive (people receiving benefits), non-active (people not working without resources) and active (people working and employed at the time of hospitalization). Schizoaffective disorder was regrouped with schizophrenia because of the small numbers of cases. Schizoaffective disorder is listed in international classifications within the categories of psychotic disorders rather than mood disorders.

Mental organic disorders were regrouped with MDD due to the small number of patients in both categories.

Data analysis:

Demographic and clinical characteristics of the patients were described with proportions for categorical variables and with means ± standard deviations (SD) for quantitative variables. The association between these characteristics and cannabis use was analyzed using univariate and multivariate logistic regression models to calculate raw and adjusted odds ratios and their 95% confidence intervals.

We then compared the average length of stay between the two groups (THC + and -) using univariate and multivariate linear regression model safter logarithmic transformation of the dependent variable (length of stay). Two multivariate models were constructed. The first model was adjusted for age, gender, lifestyle, and professional status. Psychiatric illnesses were added in the 2nd model. Adjusted least squares means were estimated from these two models and are presented after back-transformation [exp (ln (length of stay))].

Thirdly, we explored if readmission at 1 year or at 2 years could be explained by cannabis use, using univariate and multivariate logistic regression model. As previously, ORs were adjusted in a first model for age, sex, professional situation, lifestyle and, in a second model, also for psychiatric illnesses.

Finally, we examined if the class of psychotropic treatment at discharge was associated with cannabis use at admission. Univariate and multivariate logistic regression models were carried out for 4 treatment classes (antidepressants, benzodiazepines, antipsychotics and mood stabilizers).

Analyses were performed with a bilateral alpha level of 0.05 using the SAS Enterprise guide 7.15(SAS Institute, Cary, North Carolina).

Results

Description of the population:

Of the 370 patient records screened (69% men, p<0.0001), the toxicological tests identified 130 THC+ patients and 240 THC-patients. Urine was generally collected within 24 hours (mean=0.74 days, SD=1.20, IQR=0-1) following patient admission.

THC+ patients are significatively younger (p<0.0001) and had an average age of 33 years (16-57 years old) compared to 48 years (14-90 years old) for THC-patients.

Patient characteristics are shown in Table 1.

In multivariate analyses, after adjustment for all covariates, there were no differences between the two groups as regards to marital status or employment situation (Table 1).

Male patients were more often THC+ (OR = 3.48, 95CI= 2.00-6.05, p <.0001). When age was compared in terciles, the decrease in risk was particularly evident from 49 years of age (OR=0.08, 95CI=0.04; 0.17, p<.0001).

Most THC+ patients were diagnosed with schizophrenia (24.6%) or bipolar disorder (45.4%). Patients with schizophrenia showed the highest rates of positive THC screens (46.6%, 34/73). Compared to patients with schizophrenia, patients diagnosed with major depression or mental organic disorders, regrouped as "other diagnoses", were less likely to use THC at admission (OR=0.25; 95CI=0.07, 0.93; p=.04). Patients with personality disorders were also less likely to use THC at admission in crude analyses but this result was no longer significant after adjustment (OR=0.51; 95CI=0.23, 1.12; p=.09).

Among the 130 cannabis users, the concentration of THC at admission ranged from 4 to 1289 ng/mL with an average of 366.1±238.3ng/mL. The presence of other drugs, (amphetamine, heroin, cocaine, MDMA) was sought with urinary tests at admission. Illicit drugs were detected only in a few patients (n=11). 36 patients showed positive alcohol levels in blood.

Cannabis use and length of hospitalization (Table 2):

After adjustment for sex, age in terciles, marital status and professional status, THC + patients showed a longer length of hospitalization than THC-patients (mean: 11.08 vs 8.26; p=.03). However, the association disappeared after adjustment for psychiatric disorders (mean: 9.44 vs 8.04; p=.22). Sensitivity analyses show that the association of cannabis use with a longer stay persisted when adjusting only by schizophrenia (p=0.05).

There was no significant correlation between THC concentration at admission and length of stay (Spearman ρ=-0.092; p=.30).

Factors influencing rehospitalisation (Table 3):

THC+ patients at admission were more likely to be re-hospitalized at 12 months independently from demographic and clinical variables (OR=2.29; 95CI=1.24, 4.24; p=.0082). Middle-aged patients (36-48) were less likely than younger patients to be rehospitalized at 12 months (OR=0.46; 95CI=0.23, 0.89; p=.02). Concerning psychiatric disorders, patients with bipolar disorder (OR=0.46; 95CI=0.24, 0.93; p=.03), personality disorders (OR=0.27; 95CI=0.11, 0.63; p=.0025) and other diagnoses (OR=0.3; 95CI=0.09, 1.01; p=.05) were less likely to be re-hospitalized compared to patients diagnosed with schizophrenia. A similar trend was found for brief psychotic disorder.

Overall, we found similar results concerning the risk of re-hospitalization at 24 months but the association with THC+ was not significant (OR=1.62; 95CI=0.94, 2.81; p=.08) (Supplementary Table 1S).

Cannabis use and treatment prescription at discharge:

THC use at admission was associated with a more frequent prescription of benzodiazepines at discharge independently of demographic and clinical variables (OR=1.93; 95CI=1.13, 3.28; p=0.02). On the contrary, THC users were less likely to be prescribed an antidepressant at discharge (OR=0.22; 95CI=0.08, 0.66; p=.007). No association between THC use and the prescription of antipsychotics or mood stabilizers was found.

Discussion

Our purpose was to study if cannabis use influenced the evolution of patients who entered a secure psychiatric ward. To the best of our knowledge, very few studies have so far examined the effect of cannabis on patients involuntarily hospitalized, and none of them looked at the length of admission or the rates of rehospitalization.

Some studies in open hospitalization units found shorter stays among inpatients using cannabis compared to those who did not. In those studies, the selection criteria consisted on the presence of psychotic symptoms [START_REF] Rylander | The association of cannabis use on inpatient psychiatric hospital outcomes[END_REF], or discharge diagnoses of bipolar disorder, schizophrenia and other psychotic disorders [START_REF] Johnson | The Effects of Cannabis on Inpatient Agitation, Aggression, and Length of Stay[END_REF][START_REF] Deng | Hospital Stay in Synthetic Cannabinoid Users With Bipolar Disorder, Schizophrenia, or Other Psychotic Disorders Compared With Cannabis Users[END_REF]. Of note, one study found that cannabis users received less antipsychotics [START_REF] Deng | Hospital Stay in Synthetic Cannabinoid Users With Bipolar Disorder, Schizophrenia, or Other Psychotic Disorders Compared With Cannabis Users[END_REF], while another reported more agitation and oral medication in the cannabis group [START_REF] Johnson | The Effects of Cannabis on Inpatient Agitation, Aggression, and Length of Stay[END_REF]. On the other hand, a recent study in a community hospital concludes that cannabis use was associated with an increased length of stay in patients affected by schizophrenia spectrum disorders [START_REF] Olayinka | Cannabis Use in Inpatients With Schizophrenia Spectrum Disorders at a Community Hospital[END_REF]. In our sample, the association of cannabis with longer hospitalizations disappeared after adjusting for mental disorders in the multivariate analysis. Since the association between cannabis use and longer hospital stays in involuntary units was moderated by mental disorders, we conducted a sensitivity analysis to investigate specifically the effect of each diagnostic category. The association with longer hospital stays disappeared after adjusting the analyses by any or all mental disorders, except in the case of schizophrenia. This finding suggests that the use of cannabis in patients with schizophrenia may lengthen the duration of hospitalization in these units, and that the association of THC positive screens with longer hospital stays may be best explained by a higher rate of schizophrenia in this group.

Cannabis use before hospitalization predicted, independently of other variables, involuntary readmissions within 12 months. Patients diagnosed with schizophrenia were also more likely to be re-hospitalized compared to any other disorder. These results are consistent with a recent record-linkage studying Danish treatment services indicating that cannabis use is a risk marker for the readmission of patients with schizophrenia [START_REF] Rømer Thomsen | Drug-related predictors of readmission for schizophrenia among patients admitted to treatment for drug use disorders[END_REF]. Collizi et al. also suggested that a history of cannabis use prior to hospitalization increased the risk of multiple hospitalizations and extended the length of stay. This risk would be higher in men and black ethnicity [START_REF] Colizzi | Longitudinal assessment of the effect of cannabis use on hospital readmission rates in early psychosis: A 6-year follow-up in an inpatient cohort[END_REF]. However, in agreement with [START_REF] Rylander | The association of cannabis use on inpatient psychiatric hospital outcomes[END_REF], we found no effect of cannabis use on the risk of re-admission within one month of discharge (data not shown).

Few studies have reported THC concentrations among psychiatric inpatients. Duflot et al [START_REF] Duflot | Interest of adjusting urine cannabinoids to creatinine level to monitor cannabis cessation therapy in heavy smokers with psychiatric disorders[END_REF] found two-times higher concentrations among patients that were specifically hospitalized to stop cannabis abuse (many of them with psychiatric comorbidities). The average urinary concentration in their sample was 786 ± 1270 ng/mL. Independently of the psychiatric diagnosis, THC + patients were discharged more often with a benzodiazepine prescription. Benzodiazepine prescription is likely to be linked to the treatment of cannabis abstinence during hospitalization, since cannabis users are subject to withdrawal symptoms such as irritability or nervousness, insomnia and craving [START_REF] Dervaux | Cannabis use disorders and psychiatric comorbidities[END_REF][START_REF] Sexton | A Survey of Cannabis Acute Effects and Withdrawal Symptoms: Differential Responses Across User Types and Age[END_REF]. The association of cannabis use and benzodiazepine prescription emerged when age and sex were controlled for. Female and older patients received more often benzodiazepines at discharge but the prescription of benzodiazepines associated with cannabis was particularly frequent among young men and heavy cannabis users.

Two results of the multivariate analyses were unexpected. First, patients affected by depressive disorders or mental organic disorders were less likely to use cannabis compared to the other diagnostic groups. According to [START_REF] Lucatch | Cannabis and Mood Disorders[END_REF], patients suffering from depression, including bipolar depression, report higher rates of cannabis use than the general population. However, in their study cannabis use rates were substantially lower in depression compared to psychotic disorders, and no direct comparison with unaffected populations was made. Second, although few patients received antidepressants at discharge, these prescriptions were still less likely among cannabis users (only a handful of them). Given the small number of patients diagnosed with depression or receiving antidepressants, these results should be taken very cautiously.

Studies on patient compliance, in patients with both a drug use disorder and a psychotic disorder, are rare. It appears, however, that in two-thirds of cases, readmissions could be due to poor compliance [START_REF] Ameller | Attributable risk of co-morbid substance use disorder in poor observance to pharmacological treatment and the occurrence of relapse in schizophrenia[END_REF]. Cannabis use is one of the three most important explanatory factors for poor compliance in subjects after a first psychotic episode and more particularly for schizophrenia [START_REF] Miller | A prospective study of cannabis use as a risk factor for non-adherence and treatment dropout in first-episode schizophrenia[END_REF]. In schizophrenia, as much as 18% of the risk of poor compliance and approximately 30% of relapses with hospitalization could be attributable to drug use disorders [START_REF] Ameller | Attributable risk of co-morbid substance use disorder in poor observance to pharmacological treatment and the occurrence of relapse in schizophrenia[END_REF].

Our results highlight the importance of developing strategies to improve the management of cannabis use among patients with severe mental disorders. The continuity of cannabis use in this population has been clearly associated with bad adherence to treatment and care [START_REF] Barbeito | Cannabis use and involuntary admission may mediate long-term adherence in first-episode psychosis patients: A prospective longitudinal study[END_REF]. A variety of interventions, such as motivational interviews and cognitive-behavioral therapies, can be used with the aim of encouraging abstinence or reducing cannabis use [START_REF] Lee | Systematic review of outcome domains and measures used in psychosocial and pharmacological treatment trials for cannabis use disorder[END_REF].

This study is based on an unselected and relatively large sample. All patients that did not express opposition to the study were included, thus reducing selection biases. However, it is important to note three limitations. First, the immunoassays used for the urinary cannabis screen may be subject to cross-reactivity with other compounds potentially yielding false-positive results [START_REF] Saitman | False-Positive Interferences of Common Urine Drug Screen Immunoassays: A Review[END_REF]. False negative results by adulteration of the samples are also possible [START_REF] Matriciani | False-negative results in the immunoassay analysis of drugs of abuse: Can adulterants be detected by sample check test[END_REF], although improbable in our sample because of the conditions in which the screening was made.

Second, due to the retrospective nature of the study, we were unable to adjust the results by other factors such as symptom severity, other substance use or the frequency/level of cannabis use. Finally, a detailed assessment retracing the patient's consumption patterns and history would have been more reliable than a single point measure.

Conclusions:

While a lot of research has been performed on the psychiatric outcomes of cannabis use, the consequences for involuntarily treated patients have received less attention. Our data suggests the involvement of cannabis use in the unfavorable evolution of involuntary psychiatric care, increasing the risk of readmission and modifying the pattern of prescription at discharge. Nevertheless, further studies on the effect of cannabis in this population are warranted. The management strategies of cannabis use may need to be reinforced in psychiatric secure units given the specific profile of cannabis users, in terms of diagnosis, treatment and re-hospitalization.

Key points:

-Cannabis use is independently associated with benzodiazepine prescriptions at discharge and 12-month readmissions among patients involuntarily admitted to a psychiatric ward.

-Young male patients with psychotic disorders are particularly at risk of using cannabis in secure psychiatric wards.

-The systematic screening of cannabis use at admission could help to organize clinical care in these units.

Table 1 .

 1 Comparison of demographic and clinical characteristics between patients who used cannabis at the time of entry into secure care (THC+) and those who did not (THC-). Unadjusted model **Adjusted model on Sex, Age in tertiles, Marital Status, Professional status, Psychiatric disorders a OR for 10 years increase b Includes schizoaffective disorder c Includes major depression and mental organic disorders d Total percentages correspond to the sum within the column, group percentages correspond to the sum within the row. OR adjusted for sex, age, marital status, professional status, psychiatric disorders

		THC-	THC+	Total d	OR*	P-	Adjusted OR **	P-
		N=240	N=130	N=370	[95% CI]	value	[95% CI]	value
	Gender
	Male	121 (53.8%) 104 (46.2%)	225 (61%)	3.93 [2.39;6.48] <.0001 3.48 [2.00;6.05] <.0001
	Female	119 (82.1%) 26 (17.9%)	145 (39%)
	Age a	48.4±15.5	32.8±10.7		0.42 a [0.34;0.52] <.0001
	Age in terciles
	35 and less	49 (38.9%)	77 (61.1%)	126 (34%)	1		1
	36-48	82 (66.1%)	42 (33.9%)	124 (34%)	0.33 [0.19;0.55] <.0001 0.33 [0.19;0.59] .0002
	49 and older	109 (90.8%) 11 (9.2%)	120 (32%)	0.06 [0.03;0.13] <.0001 0.08 [0.04;0.17] <.0001
	Marital status
	Single	157 (60.6%) 102 (39.4%)	259 (70%)	0.52 [0.32;0.85] .0095 0.76 [0.41;1.39] 0.37
	In a relationship	83 (74.8%)	28 (25.2%)	111 (30%)
	Professional status
	Active	46 (63%)	27 (37%)	73 (20%)	1		1
	Non-active	41 (54.7%)	34 (45.3%)	75 (20%)	1.41 [0.73;2.73] 0.30 1.10 [0.51;2.39] 0.80
	Inactive	153 (68.9%) 69 (31.1%)	222 (60%)	0.77 [0.44;1.34] 0.35 0.96 [0.47;1.96] 0.91
	Psychiatric Disorders
	Schizophrenia b	39 (53.4%)	34 (46.6%)	73 (20%)	1		1
	Bipolar disorder	93 (61.2%)	59 (38.8%)	152 (41%)	0.73 [0.41;1.28] 0.27 1.00 [0.50;2.02] 0.997
	Brief psychotic episode 24 (70.6%)	10 (29.4%)	34 (9%)	0.48 [0.20;1.14] 0.10 0.52[0.18;1.48] 0.22
	Personality disorder	60 (72.3%)	23 (27.7%)	83 (22%)	0.44 [0.23;0.86] 0.02 0.51 [0.23;1.12] 0.09
	Other c	24 (85.7%)	4 (14.3%)	28 (8%)	0.19 [0.06;0.61] 0.05 0.25 [0.07;0.93] 0.04

*

Acknowledgements:

The authors are grateful for the patients of the secured psychiatric intensive care unit.

The authors would also like to thank Leonie Gazel for her help with the regulatory aspects of the study and Sarah Kabani for correcting the English version.

Declaration of interest:

Nothing to declare


Clémence Le Meur

Mélissa Cadet

Van Nguyen

Dinh Ngoc Doan

Christophe Trien

Philippe Cloquet

Alain Dillmann

T O Thote

Pryce

Nguyễn Văn Đoàn

Đinh Ngọc Triển

Christophe Cloquet

Philippe Dillmann

Alain Thote

T O Pryce

Typo-technological, elemental and lead isotopic characterization and interpretation of Đông Sơn miniature drums

Keywords: , elemental and lead isotopic characterization Vietnam, Đông Sơn culture, Protohistoric/Iron Age Southeast Asia, Copper-base metal, Microstructure, Elemental composition, Lead isotopes

Introduction

1.1 Đông Sơn culture and Iron Age Mainland Southeast Asia As per many regions of the world, the Iron Age of Mainland Southeast Asia ('MSEA'), beginning during the 5 th /4 th . c. BC, was a period of immense cultural, economic and political change, with generally sharp increases in the social complexity of regional social groups (e.g. [START_REF] Higham | The Archaeology of Mainland Southeast Asia -from 10,000 BC to the Fall of Angkor[END_REF][START_REF] Higham | Early Mainland Southeast Asia: From First Humans to Angkor[END_REF]. In addition to regional population growth, partly fuelled by innovations in intensive wet-rice agriculture stimulated by an increasingly dry climate (e.g. [START_REF] Castillo | Social responses to climate change in Iron Age north-east Thailand: new archaeobotanical evidence[END_REF][START_REF] Wohlfarth | Human adaptation to mid-to late-Holocene climate change in Northeast Thailand: The Holocene[END_REF], the beginnings of monumental combined hydraulic/defensive earthworks and evidence for rising conflict in the run up to the emergence of proto-states (e.g. [START_REF] Bellina | Khao Sam Kaeo: An Early Port-City between the Indian Ocean and the South China Sea[END_REF][START_REF] Boyd | The geoarchaeology of the Iron Age ditched sites of the Upper Mae Nam Valley, N.E. Thailand I: palaeodrainage, site lanscape relationships and the origins of the moats[END_REF][START_REF] Kim | Lasting Monuments and Durable Institutions: Labor, Urbanism, and Statehood in Northern Vietnam and Beyond[END_REF][START_REF] O'reilly | Moated sites of the Iron Age in the Mun River Valley, Thailand: New discoveries using Google Earth[END_REF], the second half of the 1 st millennium BC saw the intensification of pre-existing long-range social interaction networks, linking MSEA with South Asia, East Asia and Island Southeast Asia ('ISEA') (e.g. [START_REF] Bellina | Cultural Exchange between India and Southeast Asia. Production and distribution of hard stone ornaments (VI c. BC-VI c. AD)[END_REF][START_REF] Bellwood | Prehistory of the Indo-Malaysian Archipelago[END_REF][START_REF] Hung | Cultural Interactions in Mainland and Island Southeast Asia and Beyond, 2000 BC-AD 200[END_REF]. Given MSEA's massive ecological and cultural diversity, the presence and intensity of these Iron Age changes varied considerably, between populations occupying mountains and plains, inland and coastal zones, but the most extreme differences were, as might be expected, to be found on the extremities of the MSEA Peninsula. Located the closest to South India, widely thought to be the proximal source of MSEA iron technologies (e.g. [START_REF] Bellwood | Prehistory of the Indo-Malaysian Archipelago[END_REF][START_REF] Higham | Early Mainland Southeast Asia: From First Humans to Angkor[END_REF][START_REF] Pryce | The Metallurgical Industries[END_REF], Myanmar has provided amongst the earliest regional Iron Age dates, namely from Kan Gyi Gon in Magway Region [START_REF] Pryce | The Mission Archéologique Française au Myanmar: Past, present and future[END_REF], but even these are not significantly earlier than reliably dated sites in central and northeast Thailand [START_REF] Higham | A New Chronology for the Bronze Age of Northeastern Thailand and Its Implications for Southeast Asian Prehistory[END_REF][START_REF] Higham | A prehistoric copper-production centre in central Thailand: its dating and wider implications[END_REF]. What is now very clear, some forty years after the initial signs were spotted at Ban Don Tha Phet in west-central Thailand (e.g. [START_REF] Bellina | The archaeology of early contacts with India and the Mediterranean World from the fourth century BC to the fourth century AD[END_REF][START_REF] Glover | Ban Don Ta Phet: the 1984-85 excavation[END_REF], is that the earliest intense and sustained contacts, including limited migration, between South Asia and MSEA took place on the Myanma-Thai-Malay Peninsula, as evidenced by two decades of intensive archaeological investigation by the Franco-Thai and Franco-Myanma team in Thailand's Chumphon Province [START_REF] Bellina | Khao Sam Kaeo: An Early Port-City between the Indian Ocean and the South China Sea[END_REF]) and Myanmar's Tanintharyi Region (e.g. [START_REF] Bellina | Myanmar's earliest Maritime Silk Road port-settlements revealed[END_REF].

Concomitantly, after millennia of sustained interactions with populations of the present-day southern Chinese provinces of Guangxi and Yunnan, which led to the MSEA Neolithic [START_REF] Higham | The prehistory of a Friction Zone: first farmers and hunters-gatherers in Southeast Asia[END_REF] and Bronze Age [START_REF] Higham | Dating The Bronze Age Of Southeast Asia. Why Does It Matter[END_REF][START_REF] Higham | A prehistoric copper-production centre in central Thailand: its dating and wider implications[END_REF]Pryce et al., 2018;[START_REF] Yao | Bridging the time gap in the Bronze Age of Southeast Asia and Southwest China[END_REF] transitions, the mid-late 1 st millennium BC saw ever-heightening confluence and indeed conflict between Warring States, Qin and Han China and northern Vietnam.

Ultimately this trend culminated with the annexing of Nam Việt by Emperor Wu's armies in 111 BC, marking the beginning of the Bắc thuộc ('Northern Domination') period that was to last, with some unsuccessful disruptions, until AD 938. However, who were the Lạc Việt peoples conquered in Nam Việt, and what was the nature of their societies, before and after the imposition of direct Han control via the Han Governance of Jiaozhi ('Giao Chỉ Bộ') [START_REF] Papin | Géographie et politique dans le Viêt-Nam ancien[END_REF]. There is little doubt that some northern Vietnamese gradually adopted some Han practices in the first centuries of the Christian era, but to what extent, with what degree of fidelity, and hybridisation?

The late prehistoric chronological sequence leading to the Han Commandery in northern Vietnam is not yet precisely known. The Bronze Age, rather than Neolithic/Bronze Age status of the early-mid 2 nd millennium BC Phùng Nguyên culture remains somewhat disputed (e.g. [START_REF] Kim | The Origins of Ancient Vietnam, Oxford Studies in the Archaeology of Ancient States[END_REF] but the proceeding late 2 nd millennium BC Đồng Đậu period is widely agreed to be Bronze Age. The following period, at the outset of the 1 st millennium BC, was known as Gò Mun, which between the 8 th -6 th c. BC gave way to that of the Đông Sơn. This latter, persisted at least until the beginning of the Eastern Han period (AD 25). The eponymous site of this period, which also gave its name to the iconic copper-base drums of various sizes that continue to serve as the image of late prehistoric Vietnam, provides the bulk of the study assemblage for this paper. The 'Đông Sơn drum' artefact class, whose ultimate origin and social meaning has been hotly debated for over a century, is claimed to have been found across southwestern China, MSEA and much of ISEA (e.g. Bernet Kempers, 1988;[START_REF] Calò | Trails of Bronze Drums Across Early Southeast Asia: Exchange Routes and Connected Cultural Spheres[END_REF][START_REF] Heger | Alte Metalltrommeln aus Südostasien[END_REF][START_REF] Jusoh | Bronze Drum in Selangor (Malaysia): The Motif and Significance from Archaeological Perspective[END_REF][START_REF] Oliveira | Dong Son drums from Timor-Leste: prehistoric bronze artefacts in Island Southeast Asia[END_REF][START_REF] Pirazzoli-T'serstevens | The bronze drums of Shizhai sahn, their social and ritual significance[END_REF][START_REF] Sinh | Lead bronze alloys, the Hung Kinh and Dong Son Culture (in Vietnamese)[END_REF].

Regional copper-base drums were initially classified by F. [START_REF] Heger | Alte Metalltrommeln aus Südostasien[END_REF] into various types, I -IV, with Is being the oldest and later types continuing to be used for rituals in many ethnic minority populations, often in upland and remote regions (e.g. [START_REF] Andaya | The Social Value of Elephant Tusks and Bronze Drums among Certain Societies in Eastern Indonesia. Bijdragen tot de taal-, land-en volkenkunde[END_REF][START_REF] Izikowitz | Lamet: Hill peasants in French Indochina[END_REF]. Closer reading soon reveals the ancient, Heger I, drums are typically referred to as either 'Đông Sơn' or 'Dian' (Yunnan) bronzes (typically but not exclusively leaded bronze alloys), as there are clear stylistic differences between the two, but discussion continues on which was the earliest type [START_REF] Han | Who Invented the Bronze Drum? Nationalism, Politics, and a Sino-Vietnamese Archaeological Debate of the 1970s and 1980s[END_REF] and on the production technique (e.g. [START_REF] Bennett | Bronze casting technology in protohistoric Southeast Asia, the technology and its origins[END_REF][START_REF] Chiou-Peng | Dian bronze art: its source and formation[END_REF]. The dating is difficult to resolve satisfactorily as whilst the Yunnan Metal Age is increasingly well-dated [START_REF] Yao | Bridging the time gap in the Bronze Age of Southeast Asia and Southwest China[END_REF], Metal Age Vietnam continues to suffer from a lack of reliable radiometric dating [START_REF] Kim | The Origins of Ancient Vietnam, Oxford Studies in the Archaeology of Ancient States[END_REF], with some notable exceptions like Đọng Xá [START_REF] Bellwood | Ancient Boats, Boat Timbers, and Locked Mortise-and-Tenon Joints from Bronze/Iron-Age Northern Vietnam[END_REF]. Indeed, Đọng Xá is a Red River Delta site that produced a drum of Dian rather than Đông Sơn style and of an atypical elemental and lead isotopic composition, so the devil is clearly in the detail [START_REF] Pryce | More questions than answers: the Southeast Asian Lead Isotope Project 2009-2012[END_REF]. This period also corresponds to the Hallstatt Plateau (e.g. [START_REF] Jacobsson | Refining the Hallstatt Plateau: Short-Term 14C Variability and Small Scale Offsets in 50 Consecutive Single Tree-Rings from Southwest Scotland Dendro-Dated to 510-460 BC[END_REF], so without targeted chronological campaigns, preferably combining radiocarbon with dendrochronology and Bayesian stratigraphical statistical analysis, we are unlikely to see an entirely satisfactory resolution to the question of which drum tradition came first.

For the question of technology, opinion splits between piece-mould casting [START_REF] Meyers | Casting technology in Cambodia and related Southeast Asian Civilizations[END_REF][START_REF] Nguyễn | trình đúc trồng đồng Đông Sơn the hướng tiép cận thực nghiệm dân tộckhảo cổ học (Ethnoarchaeological approach of the Đông Sơn bronze drums casting technique)[END_REF], long known in the Bronze Age Central Plain of China, or lost wax casting, whose origin is less clear but potentially Southeast Asian (e.g. [START_REF] Barnard | The entry of cire-perdue investment casting, and certain other techniques (mainly metalworking) into south China and their progress northwards[END_REF][START_REF] Bennett | Bronze casting technology in protohistoric Southeast Asia, the technology and its origins[END_REF][START_REF] White | Early East Asian Metallurgy: The Southern Tradition[END_REF][START_REF] Notis | Ancient Chinese Bronze Casting Methods: The Dilemma of Choice[END_REF] or Chinese [START_REF] Peng | Metalworking in Bronze Age China: The Lost-Wax Process[END_REF]. Here is not the place to go into the details of these two broad techniques, for which a large literature exists. Needless to say, no single scholar has made an exhaustive technological, let alone archaeometric, study of the hundreds of known large drums, such is their wide geographical distribution, across Southeast Asia and Western museums, and the inaccessibility of examples in private collections. As such, the important potential for variation in production technique, or combinations of decorative style, techniques and materials, remains unexplored. This lacuna could well obscure multiple production centres, and/or core-periphery interactions as expressed via imitations or re-interpretations of imported material culture. Of the limited archaeometric studies available (e.g. [START_REF] Pryce | More questions than answers: the Southeast Asian Lead Isotope Project 2009-2012[END_REF], those from peninsular Thailand (Pryce and Bellina, 2018) and Bali (Pryce et al., 2018) bear out these possibilities, as do findings of drums moulds from the Non Nong Ho site in northeastern Thailand [START_REF] Baoneod | Hand-In-Hand: conservation and development for local cultural heritage of Na Udom, Nikhom Khamsoi[END_REF][START_REF] Lertlum | Non Nong Hor Archaeological Site, Ban Na Udom, Amphoe Nikom Khamsoi[END_REF]. This paper takes a different direction to preceding efforts, in that the entire sub-class of miniature drums constitutes the study assemblage. Ninety percent of all known miniature drums have been directly studied by the authors, and nearly 20% of the total has been subjected to stylistic, technological, elemental and lead isotope analyses at a much higher level of representativity. Such a focus, on artefacts that are only found in cemeteries in a restricted area of the Red River Delta, as opposed to the large drums' regional distribution, may be able to shine light, not only on the possibility of production variation in large drums, but also on the nature of the Han occupation of northern Vietnam, as funerary miniatures are a well-known Han trait (e.g. [START_REF] Selbitschka | Miniature tomb figurines and models in pre-imperial and early imperial China: origins, development and significance[END_REF].

Đông Sơn site

The cemetery at Đông Sơn village (105.78295° E, 19.84934° N) in Thanh Hóa province Subsequent Đông Sơn excavations in 1959, 1961-1962, 1969-70 and 1976 by the Institute of Archaeology of Hanoi, expanded the known extent and understanding of the site. A total of 129 tombs were recorded over an area of 2033 m². Unfortunately, very few human bones were preserved, making it impossible for a solid study of age and sex profiles to be conducted. The cemetery presented three strata with superposed and intercutting burials suggesting a phase of use ranging from a period qualified as 'pre-Đông Sơn' to the Han occupation period. Regrettably there are no available radiocarbon dates for the site. The miniature drums, for those we have excavation records, were found in indigenous tombs and were clearly intended as burial offerings.

(Figures 1 & 2

Thiệu Dương and Lãng Ngâm sites

Thiệu Dương is a cemetery site in the hamlet of Du ̛ơng Xá (19.859722°N, 105.760556° E), Thiẹû Du ̛ơng village, Thanh Hoá province, located a few kilometres away from the Đông Sơn site. It was discovered during the French colonial period and excavated three times by a team lead by the Vietnamese Institute of Archaeology, between 1960 and 1965. A total of 123 burials from the late Đông Sơn period were discovered in an area covering more than 3000 m² [START_REF] Reinecke | Schätze der Archäologie Vietnams (Treasures of Vietnamese Archaeology)[END_REF][START_REF] Tỳ | Báo cáo khai quật khảo cổ di chỉ Thiệu Dương (Thanh Hoá) (Thiệu Dương site excavation report (Thanh Hoá)), Viện khảo cổ học. Uỷ ban khoa học xã hội việt nam[END_REF]). Among 444 copper-base artefacts, one miniature drum was found in an adult grave. Notably this grave also contained the largest number of metal artefacts within the site. One other miniature was found in 1925 during Pajot's excavations but its location is unknown. Another chance find is known of but is not documented.

Lãng Ngâm is a cemetery site in Núi Thiên Thai hamlet (106.168753° E, 21.074227°N), Lãng Ngâm village, Bắc Ninh, province. It was excavated in 1972 by the National History Museum in Hanoi (Bảo tàng Lịch sử Quốc gia), after the reporting of a chance find. In the limited area excavated, four burials were recorded, one of which contained a miniature drum [START_REF] Huyền | Văn Hoá Đông Sơn tính thống nhát và đa dạng (The culture of Đông Sơn : unity and diversity). Nhà Xuất Bản Khoa Học Xã Hội[END_REF].

Assemblage

There is no formal definition regarding the dimensions of miniature drums, though Phạm Minh Huyền et al. (1987: 120-122) andBernet Kempers (1988: 45) suggest a maximum height of 150 mm or a tympanum diameter of 200 mm, respectively. In this study we propose that miniature drums are those less than 200 mm in height, which gives a clear differentiation from their larger counterparts whose height is considerably more and can even exceed 600 mm. As per the large drums, the miniature are hollow, though in a few cases baked clay probably corresponding to the casting core remains. The miniature drum assemblage, their contextual information and method of typological classification, in particular their casting technique, will be dealt with at length in Le Meur et al. (forthcoming), so we will limit ourselves here to the details necessary to cross-reference the archaeometric approach that is the focus of this paper. A total of 131 drum miniatures are known, of which 118 were personally examined by the lead author. The remaining 13 are known either from bibliographic sources, or through correspondence with museum curators. 53 of the 131 examples come from archaeological excavations, with the remainder being the result of chance finds, donations, private collections and police seizures of looted material. The major repositories for the drum miniatures are the National History Museum, the Thanh Hóa provincial museum, and the Cernuschi Museum in Paris, whose combined collections constitute 78% of the total. All of the 25 samples whose analyses are presented here come from the National History Museum and were legally sampled and exported to France in November 2018. This gives an archaeometric study ratio of ca. 19%, which is high compared to most regional assemblages and offers an rare level of representativity (e.g. [START_REF] Pryce | More questions than answers: the Southeast Asian Lead Isotope Project 2009-2012[END_REF].

The five miniature drum types, plus exceptional and non-classifiable examples are shown in Figure 2. They may be defined thus: Type 1 drums have a ring on the tympanum, no seams, a flat tympanum, a rounded profile upper mantle, a truncated cone shape lower mantle and a wide foot. Hollow designs cover the tympanum and, most of the time, the mantle. The quantity and appearance of handles are varied, with no pattern identified. Sub-types have been created considering the presence of frog figurines on the tympanum (Type B) or the significant height of the upper mantle (Type C). Type D gathers incomplete drums associated to Type 1 due to the presence of a ring or their morphological characteristics.

Type 2 drums have neither seams nor decoration, a very flat and large tympanum and two symmetric handles. Considering the shapes, two sub-types have been identified. Sub-type A includes drums with a sharp oblique upper mantle. As the shape of the lower mantle differs between cylindrical and truncated cones, associated with a wide foot differentiated by an inflection from the lower mantle or included in the lower mantle base, two groups have been created. Sub-type B consists of drums with oblique rounded upper mantle, truncated cone-shaped lower mantle from which foot is not stressed.

Type 3 drums bear a single seam bisecting the drums vertically, were undecorated and have a slightly convex tympanum associated with an oblique rounded upper mantle. As the number of handles and the shape of the lower mantle differs, four sub-types have been created (Figure 3). The first one includes drums with two handles between the seam, with a cylindrical lower mantle and a wide foot or with a truncated cone-shaped lower mantle with no foot emphasised by an inflexion. Sub-type Bs have only one handle disposed between the seam, and two shape have been identified as in sub-type A. Drums gathered in sub-type C have two handles on the seam, a cylindrical lower mantle and a wide foot emphasised by an inflexion. Sub-type D drums are similar to sub-type A1 drums in shape, but are bigger and does not have handles attached to the upper mantle and the lower mantle but only on the lower mantle.

Type 4 drums have three seams, no decoration, a tympanum slightly heightened and a rounded upper mantle. Two sub-types have been created considering the different shapes of the lower mantle and the foot (Figure 4). Type 5 drums have three seams and designs in relief are always present on the tympanum, and frequently on the mantle. The large and various shapes of the upper mantle, lower mantle and foot, lead us to identify four sub-types. Sub-type A have raised tympana, rounded upper mantles, cylindrical lower mantles and wide feet so as a star at the centre of the tympanum and two handles disposed between the seams, contrary to sub-type B with two handles on the seams, a flat tympanum, an oblique rounded upper mantle, a truncated cone shape lower mantle and designs both on the tympanum and the lower mantle. Subtype C drums carried a shape similar to sub-type A but are bigger, and the tympanum surface is decorated with a star and other geometric designs. Sub-type D consists of drums with heightened tympanums, four handles, decorated on the tympanum and the mantle.

Those are the only examples to have four flying bird designs on the tympanum. Body shapes differed so we have divided this sub-type in three sub-groups. The first one of small drums, with oblique rounded upper mantles associated with wide lower mantles. Drums belonging to the second group are the largest our assemblage, with rounded upper mantles, a truncated cone shape lower mantle with a wide foot highlighted by an inflexion. The last Type 5 D group include drum similar to Type 5 B with a significant addition, four frog figurines on the tympanum.

Two more categories have been added for drums not associated to one of the five types (Incategorizable) and for drums which stand out (Exceptional). As can be seen in Figure 4 (left), Type 1 drums are the predominant type, followed by Type 5s, 3s and 2s tied, and Type 4s the least common. Details of the analysed samples can be found in Table 1, and it can be seen (Figure 4, right) that our sampling strategy at the National History Museum followed the overall type distribution closely, with the exception of Type 2s being under-represented and Type 3s over-represented, which was simply due to the unavoidable sub-sampling issue of being granted permission to cut only in Hanoi. We can notice the particular shape and aspect of one of the two Remarquable drums sampled (Figure 4) compared to the ones associated to the five types.

Methodology

The studied artefacts were all cut on site in the National History Museum, Hanoi, using an ultra-fine jeweller's saw, taking into account areas of existing damage (preferred) and corrosion (avoided). As such it was not possible to cut the artefacts across macroscopicallyvisible seams and/or decoration so as to get microscopic proof of production technique. The artefacts were immediately restored with copper oxide dust-impregnated dental wax. The cut samples were 2-4 mm 3 , cut from exterior surfaces and may not be representative of object heterogeneity due to poor alloy mixing, segregation during solidification, or any unidentified joints or welds. The cut samples were then halved, for elemental/microstructural and isotopic analyses, respectively.

Optical Microscopy (OM)

Cut samples were epoxy resin-mounted and ground using silicon carbide wet-dry paper (80-4000 grit), prior to polishing with diamond pastes (3, 1 and 0.25 µm). The microstructure was studied by OM before (for corroded samples) and after ferric chloride etching to reveal crystalline structures. 2). Good results for majors and minor components were confirmed but note that light elements at low concentrations like phosphorous, silicon, aluminium, magnesium and also sulphur were not reliably detected due to non-vacuum conditions. The analyses were performed on the OM mounted and polished sections using a 3 mm beam diameter, which allowed for reliable results as long as the sample was larger than this. Three such spot analyses were made for each sample to account for corrosion and inclusions.

Scanning Electron Microscopy with Energy Dispersive Spectrometry (SEM-EDS)

The OM/XRF samples were carbon coated for analysis in a JEOL 7001F instrument, in order to establish the bulk composition of samples less 3 mm in diameter, those with intergranular corrosion, and to study any inclusions. Both secondary electron (SE) and backscattered electron (BSE) modes were used, using a 20 kV accelerating voltage, a 10 mm working distance with an Oxford Silicon Drift Detector, and processed using Oxford Instruments Aztec software. The detection limit was fixed at 0.5 wt.% with a count rate of 4000/s (detection time of 40 s), which gave good spectral resolution with respect to background noise. We consider the relative quantification error (2 σ) is circa 10% of the measured value. SEM-EDS accuracy was evaluated using the same CRMs as used for the pXRF analysis, and we obtained good results for the major elements (Table 2). Bulk compositions for each sample were obtained by a mean of 3-4 areas scan (0.4 mm 2 ) per sample. The analyses were performed in areas without corrosion products, when it was possible, as it can have an effect on the SEM results, especially on the major components. France, using MC-ICP-MS after lead extraction [START_REF] Manhes | Lead isotope study of basic-ultrabasic layered complexes: Speculations about the age of the earth and primitive mantle characteristics[END_REF]. Thallium NIST SRM 997 was used to correct for instrumental mass bias and all parameters were adjusted to obtain the closest values relative to NIST SRM 981, as determined by DSTIMS [START_REF] Thirlwall | Multicollector ICP-MS analysis of Pb isotopes using a 207Pb -204Pb double spike demonstrates up to 400 ppm/amu systematic errors in Tl-normalization[END_REF].

More details about SARM-CRPG lead isotope analysis are available in [START_REF] Cloquet | Atmospheric pollutant dispersion around an urban area using trace metal concentrations and Pb isotopic compositions in epiphytic lichens[END_REF][START_REF] Pienitz | Disruption of the geochemical metal cycle during mining: Multiple isotope studies of lake sediments from Schefferville, subarctic Québec[END_REF].

As one case study within the SEALIP/BROGLASEA programme, LIA was used to look for 'consistency' with known and characterised production systems, in recognition that there could be other, as yet uncharacterised, primary and/or secondary production systems, as well as recycling impacting interpretation (e.g. [START_REF] Budd | Evaluating lead isotope data: further observations[END_REF][START_REF] Pryce | More questions than answers: the Southeast Asian Lead Isotope Project 2009-2012[END_REF][START_REF] Pryce | Southeast Asia's first isotopically-defined prehistoric copper production system: When did extractive metallurgy begin in the Khao Wong Prachan Valley of central Thailand?[END_REF][START_REF] Wilson | Handbook of Archaeological Sciences[END_REF].

Results

Optical Microscopy

As was expected given the typology and decoration of the miniature drums, all presented ascast microstructures with no evidence for post-casting treatment (Figure 5). Some variation is visible in the speed of cooling, with dendrites indicating extended cooling, preheated moulds and/or lack of quenching/immediate breaking of the moulds. At higher magnifications, elemental segregation is visible, as would be expected with longer cooling times. Inter-granular corrosion is frequent and some samples are almost exclusively composed of corrosion products (DS/9, THD/2, DS/8 and DS/19), potentially impacting the XRF elemental analyses (see below), as would the relatively common fully-segregated lead prills, formed due to Cu-Pb solid-state immiscibility. The dimension of lead nodules is variable and dependent on the cooling rate, the slower the cooling rate is the larger are the lead nodules (Mille, 2017: 383). Some samples have a two-phases microstructure, namely the α+δ eutectoid, with a brittle and hard high-tin δ phase and a rich-copper α phase. The quantity/area of these second phase in some samples is also indicative of fast cooling rates.

For every sample (except those composed exclusively of corrosion products), copper sulphide inclusions are observed with rounded and polylobed form The studied assemblage contains four classes of copper-base alloy using the standard 1 wt% as the cut-off for alloying components: 1. Effectively pure copper, 2. Bronze, 3. Leaded copper and 4. Leaded bronze. Table 1 shows both bulk (XRF) and phase (SEM-EDS) elemental results, which sometimes differ considerably, which highlights the level of corrosion.

Elemental analyses -XRF + SEM-EDS

However, only in two cases, DS/12 and DS/19, does this potentially change the alloy identification, and in realistic 'borderline' terms, it can be considered not to. Overall, there is a clear trend towards leaded alloys, at 81% of the assemblage (Figure 6). In provenance terms, this means that our LIA data must be discussed largely with respect to lead exchange systems, though no prehistoric lead production systems have yet been studied [START_REF] Pryce | Metallurgy in Southeast Asia[END_REF][START_REF] Pryce | Proceedings of the 5th Forbes Symposium on ancient Asian bronzes[END_REF] as well as those for copper/bronze. In terms of standardisation, there is near continuous variation in tin content from below detection limit (bdl. XRF/SEM-EDS) to 21 wt.% (Figure 7). The samples with the higher tin concentrations are not true 'high-tin bronzes' in the sense of the hot-worked and quenched beta alloys often associated with the Indian subcontinent [START_REF] Murillo-Barroso | Khao Sam Kaeo -an archaeometallurgical crossroads for trans-asiatic technological traditions[END_REF]Pryce and Bellina, 2018;[START_REF] Srinivasan | Wrought and quenched, and cast high-tin bronzes in Kerala State, India[END_REF]: the high Sn values are simply due to copper depletion and apparent enrichment of residual tin oxide in the burial environment. Tin values measured by SEM-EDS in less corroded metal do not exceed 15 wt%. Similar but not quite identical results can be seen for lead content, from bdl. to 18 wt.%, perhaps some modalism at ca. 1-2, 6-8 and 10-12 wt. % lead compositions (Figure 8), though corrosion depletion of copper remains the most likely reason, as seen in the optical microscopy. In Table 1 we include a column for 'Alloy-Type', that is cross-referencing the typological classification and the alloy, to see if there were preferred 'recipes' for certain shapes. This could potentially identify control of alloying to achieve more complex shapes, and/or the practices of individual workshops. Although there is a predominance (31%) of leaded bronze Type LB1 miniature drums this is most likely a simple function of Type 1 being the prevalent artefact class and leaded bronze being a very common Iron Age MSEA alloy [START_REF] Pryce | Metallurgy in Southeast Asia[END_REF][START_REF] Pryce | More questions than answers: the Southeast Asian Lead Isotope Project 2009-2012[END_REF]. As such, with these data we see no correspondence between style and alloy (Figure 9).

Lead isotopes

Complete raw lead isotope ratio data may be consulted in Table 3, alongside the 'Alloy-Type' column seen in Table 2. Being a four-fifths leaded assemblage, we are clearly limited but not mute, in what we can say about the sources of the primary alloy component, copper, whose own trace lead isotope signature will be totally overwhelmed by that of the added lead metal. Let us begin then by assessing the general clustering of the study assemblage, as labelled for leaded and unleaded artefacts (Figure 10). Without reference to a regional database, not a great deal could be said other than that the sources of copper for DS/13, THD2 and DS20, itself perhaps with THD/1, are probably different. Likewise, we can see two main lead clusters to the left and centre of the figure, with possible outliers in DS/2 and DS/6. These a priori potential consistencies show no correspondence with the attributed typological classification. Considering the unleaded examples, of which there are only five, we can at least assess consistency with the Southeast Asian copper production LI database (Figure 11, see [START_REF] Cadet | Laos' central role in Southeast Asian copper exchange networks: A multi-method study of bronzes from the Vilabouly Complex[END_REF][START_REF] Pryce | More questions than answers: the Southeast Asian Lead Isotope Project 2009-2012[END_REF][START_REF] Pryce | Southeast Asia's first isotopically-defined prehistoric copper production system: When did extractive metallurgy begin in the Khao Wong Prachan Valley of central Thailand?[END_REF]Pryce et al., , 2011a;;[START_REF] Zou | Investigation of early Bronze Age civilizations in Yunnan: a scientific analysis of metallurgical relics found at the Guangfentou ruins in Jiangchuan[END_REF]. Here we see that DS/13 appears to lie within the LI signature as well-defined for the Vilabouly Complex in central Laos [START_REF] Cadet | Laos' central role in Southeast Asian copper exchange networks: A multi-method study of bronzes from the Vilabouly Complex[END_REF]Pryce et al., 2011a) but the correspondence is actually with artefacts that are considered exotics at that site, probably imports, and thus we have a comparison for consumption but not production (provenance). Likewise, for DS/10 and THD/2, which plot close to the Vilabouly Complex signature, but not close enough as to be considered consistent with it, especially as this area of the plot is very highly populated when taking the whole regional database into account. Phu Lon, in northeastern Thailand, has always had a poorly defined LI field due to a reliance on excavated mineral samples of uncertain human use as opposed to slag samples [START_REF] Pigott | Mining archaeology in geological context. The prehistoric copper mining complex at Phu Lon, Nong Khai Province, northeast Thailand[END_REF]Pryce et al., 2011a), as well as multiple hydrothermal depositional episodes in geological time giving a dispersed and radiogenically-trending plot [START_REF] Kamvong | The origin and evolution of skarn-forming fluids from the Phu Lon deposit, northern Loei Fold Belt, Thailand: Evidence from fluid inclusion and sulfur isotope studies[END_REF]. Nevertheless, THD/1 is relatively consistent, as much as individual samples can be, with TH/PL/11, which was one of the rare slag samples, and as such an indication of the anthropogenic Phu Lon copper signature (Pryce et al., 2011a). Likewise, both THD/1 and DS/20 are not unreasonable candidates for the recently published Guangfentou copper production signature, from south of Kunming in Yunnan Province, PRC [START_REF] Zou | Investigation of early Bronze Age civilizations in Yunnan: a scientific analysis of metallurgical relics found at the Guangfentou ruins in Jiangchuan[END_REF]. The Guangfentou slag samples exhibit high variation LI ratios, which, as the authors acknowledge, is indicative of variable ore feedstock.

However, given known close associations between north Vietnamese Đông Sơn and

Kunming-centred Dian culture (e.g. [START_REF] Calò | Trails of Bronze Drums Across Early Southeast Asia: Exchange Routes and Connected Cultural Spheres[END_REF][START_REF] Chiou-Peng | Dian bronze art: its source and formation[END_REF][START_REF] Yao | The Ancient Highlands of Southwest China: An Archaeological History from the Bronze Age to the Han Empire[END_REF] it is perfectly reasonable to expect some movement of metals, either raw or processed, over the 500-600 kilometres separating the two areas, especially as most can be accomplished afloat on the Red River. Nevertheless, none of the present study's copper-base samples can be considered to be reliably provenanced.

Figure 11: Lead isotope rations for the copper-base study samples and known regional primary copper production centres : the Khao Wong Prachan Valley in central Thailand (NKH and NPW), Phu Lon in northeastern Thailand (PL), the Vilabouly

Complex in central Laos (PBL and TNN) and Guangfentou in central Yunnan (GFT)(data from [START_REF] Cadet | Laos' central role in Southeast Asian copper exchange networks: A multi-method study of bronzes from the Vilabouly Complex[END_REF][START_REF] Pryce | More questions than answers: the Southeast Asian Lead Isotope Project 2009-2012[END_REF][START_REF] Zou | Investigation of early Bronze Age civilizations in Yunnan: a scientific analysis of metallurgical relics found at the Guangfentou ruins in Jiangchuan[END_REF].

In terms of lead production centres, as previously stated, none have yet been studied in Southeast Asia [START_REF] Pryce | Metallurgy in Southeast Asia[END_REF][START_REF] Pryce | Proceedings of the 5th Forbes Symposium on ancient Asian bronzes[END_REF]. Some unpublished LI data for lead minerals (galena) by Dr Tom Chase under the aegis of the Thailand Archaeometallurgy Project during the mid-1980s (courtesy of Prof. Vincent C. Pigott) offer no consistency with our study samples but these are not proven anthropogenic lead signatures and this whole field remains massively understudied at a regional scale -i.e. there are known and/or suspected pre-modern lead production sites but none have been investigated yet (Figure 12). Of course, a considerable proportion of the complete recent SEALIP/BROGLASEA database consists of leaded alloys (e.g. [START_REF] Cadet | Laos' central role in Southeast Asian copper exchange networks: A multi-method study of bronzes from the Vilabouly Complex[END_REF]Pryce et al., 2018;Pryce and Bellina, 2018), and these offer some potentially useful insights (Figure 13). There is substantial variability, overlap and outliers but the Đông Sơn and Thiệu Dương samples have a distinct tendency to form an 'upper' (higher 207 Pb/ 204 Pb) cluster and are consistent with a number of continental and littoral Thai and one Cambodian site, whereas as the bulk of the previously studied Vietnamese leaded copper-base alloys fall in a 'lower' cluster. It should be noted that the Pacung site is on Bali, and thus at quite some distance (ca. 3400 km geodesic) from the Red River delta but such maritime links have been previously proposed [START_REF] Calò | Trails of Bronze Drums Across Early Southeast Asia: Exchange Routes and Connected Cultural Spheres[END_REF] and potentially detected (Pryce et al., 2018). Finally, we can drill down into these, predominantly leaded data, to compare the Đông Sơn drum miniatures to the, albeit limited, medium and large-sized drum population of the SEALIP/BROGLASEA database for which elemental and lead isotope datasets exist (Figure 14, N=12 out of hundreds of stylistically reported examples e.g. [START_REF] Calò | Trails of Bronze Drums Across Early Southeast Asia: Exchange Routes and Connected Cultural Spheres[END_REF]. Again, these larger drums have a range of alloy types: copper, leaded copper and leaded bronze, thus representing Cu and Pb exchange systems, and three (VN/DX/10, ID/ML/4 & ID/ML/5) are not considered to be of the Đông Sơn style [START_REF] Pryce | More questions than answers: the Southeast Asian Lead Isotope Project 2009-2012[END_REF]Pryce et al., 2018). Firstly, we note a cluster of four Đông Sơn leaded miniatures (DS/5,7,14 & 17) in apparent compatibility with a single drum, LA/VC/13, from the central Lao Vilabouly Complex [START_REF] Cadet | Laos' central role in Southeast Asian copper exchange networks: A multi-method study of bronzes from the Vilabouly Complex[END_REF]. Secondly, we observe that the bulk of the Đông Sơn leaded miniature assemblage plots near to TH/KS/2. This is a false match as this peninsular Thai drum was made from near pure copper, itself consistent with the Vilabouly Complex signature, and may have been a poorly-executed ancient imitation (Pryce and Bellina, 2018). Generally, there is some lead isotope consistency between the miniature and large drums but far more large drum data are needed. Of note, however, is the complete incompatibility of VN/DX/10, a large unleaded bronze drum found in northern Vietnam but with Dian-style decoration [START_REF] Pryce | More questions than answers: the Southeast Asian Lead Isotope Project 2009-2012[END_REF]. DX/10 does plot broadly within the newly characterised Yunnanese Guangfentou copper production signature (Figure 11), though many more such analyses are needed to reinforce this, admittedly enticing, association.

Figure 14: LI ratios of medium/large vs miniature leaded and unleaded drums (data from [START_REF] Pryce | More questions than answers: the Southeast Asian Lead Isotope Project 2009-2012[END_REF][START_REF] Pryce | Copper-base Metallurgy in Metal-Age Bali: Evidence from Gilimanuk, Manikliyu, Pacung, Pangkung Paruk and Sembiran[END_REF]Pryce and Bellina, 2018).

5-Discussion

5.1-Đông Sơn miniature drum production: regular workshops or random funereal alloying practices?

In 2014, the excavation at Luy Lâu (or Lien Laû) Citadel in Bắc Ninh Province, led by the National Museum of History and the Japanese University of East Asia, uncovered the remains of a drum foundry, the first of its kind (Reinecke, 2016: 457-458). Previously, only two fragments of an investment clay drum mould had been recovered from the same site, only 30 meters away [START_REF] Masanari | đúc trống đồng được phát hiện trong lòng thành cổ Liên Lâu [Casting mould of a bronze drum discovered in the ancient citadel of Liên Lâu[END_REF]2011: 164-167). These recent discoveries tend to confirm that some of the big-sized Đông Sơn bronze drums were cast by piece moulds.

Due to the significant difference in scale, it is evident miniature drums do not imply the same type or mastery of technical skills as large drum production. For the latter, whatever the casting method used, merely the melting and pouring of dozens of kilograms of metal, synchronised to avoid cold-shuts in the fine-walled finished product, implies significant technical skill and organisation of production. For the miniatures, the lack of 'alloy-type' correspondence suggests the metal used in their manufacture was probably recycled. The risks involved in these much smaller castings were far lower, not requiring particular alloys to have a reasonable chance of success, and thus we can imagine these artisans using whatever copper-base scrap was available to them. Should we, therefore, consider miniature drums as technically uninteresting and socially irrelevant, as opposed to the prestige so often associated to large drums? We think this would be an error, for a number of reasons. Firstly, there is the admittedly subjective element of production quality. In particular, the typological study highlighted two types within the corpus, 1A & 5D, whose decoration and lack of any casting failures suggest they were made by a reasonably competent artisan. Secondly, the central ring on the tympanum of the type 1 miniatures may indicate a real difference in their use, possibly as suspended bells with the general appearance of a miniature drum. This could indicate an evolution of traditional use and external influences in musical instruments during a period of deep cultural change (i.e. the Han occupation of northern Vietnam). Thirdly, the apparently poor technical execution of the other miniature drum types does not necessarily imply low social value. As noted, the Thiẹû Du ̛ơng example was found in the richest burial of 123 excavated.

Miniature drums have rarely been discovered in the same burials as their large counterparts, for which they presumably stood in as models but nevertheless attest to the importance of drums for the Lạc Việt people.

The range of miniature drum production indicates that Lạc Việt craftspersons used multiple methods to produce material culture that would normally be categorised as a single, simple type (Le Meur et al, forthcoming). These variations of style, technology, alloy type and raw material sourcing are important, and rarely considered by archaeologists, as they suggest multiple and overlapping communities of practice. Lạc Việt people maintained contact with other 'drum cultures', as the miniature drum classified as 'Exceptional' was probably made in Yunnan or inspired by Yunnan examples.

By a reimagining of the size and the use of drums, and their lack of morphological and technical standardisation, the north Vietnamese phenomenon of drum miniaturization seems to be slightly but importantly different from Han funerary customs. The question of the miniature drums' function remains, as does their importance within the broader 'drum cultures' of northern Vietnam and southern China. These leads will require a much larger study of well-contextualised north Vietnamese mid-late 1 st millennium BC burial assemblages containing drums, for comparison with southern Chinese funeral practices.

Relation to wider Southeast Asian metal exchange networks

At this point in the SEALIP/BROGLASEA programme, there is little detailed geochemical interpretation that can be given of the miniature drums at a regional level. The present assemblage is majority leaded copper alloy and we lack primary production signatures for lead. Nevertheless, those leaded, and unleaded, consumption signatures fall into the very dense cloud of data that makes up the bulk of the Southeast Asian non-ferrous/non-precious metals dataset -the miniatures drums are coherent with their regional context. The imminent, at the time of writing, receipt of Yunnan artefact analyses will greatly aid our ability to resolve chemical clustering issues, and forthcoming multifactorial network analysis [START_REF] Radivojević | Community structure of copper supply networks in the prehistoric Balkans: An independent evaluation of the archaeological record from the 7th to the 4th millennium BC[END_REF] will enable typological, chronological and geographical aspects to be taken into account.

Conclusion

The present study represents the first comprehensive multi-method study of a discrete Đông Sơn culture metal assemblage. Our study of all 131 known examples of miniature drums identified five main morpho-stylistic groups, encompassing three broad technological traditions: lost wax, bivalve and multiple piece moulding. Four alloy classes were identified in samples of varying corrosion: copper, bronze, leaded copper and leaded bronze; the latter predominating in an ca. 80% leaded alloy assemblage. Twelve 'alloy-types' were identified, with LB1 (leaded bronze Type 1) drums being the most common. Lead isotope analyses identified two main leaded alloy groups, and two unleaded groups, the latter of which may offer some consistency with Yunnan copper production. In summary, the miniature drums show high variation in form, decoration, production methods and materials that suggest an intriguing intersection in indigenous and exotic artisanal and burial practices at a critical juncture in Vietnamese history.

SAMPLE

Figure 1 :

 1 Figure 1: Map of Vietnam (red outline) in geographical relation to Mainland Southeast Asia and East Asia (top), and the Red River delta and the principal site's location (bottom).

  ) was first investigated by Louis Pajot, a French colonial officer assigned by the Ecole Française d'Extrême-Orient (EFEO) to supervise the discovery of archaeological remains in this province between 1924 and 1928. Following criticism over a lack of professionalism, the EFEO engaged the Swedish archaeologist Olov Janse to succeed Pajot in 1935. Two burials and 16 funeral deposits were identified and associated to the Đông Sơn occupation period.

Figure 2 :

 2 Figure 2: Analysed miniature drums typology (from Le Meur's forthcoming doctoral thesis).

Figure 3 :

 3 Figure 3: Miniature drum typological classification schematic (from Le Meur's forthcoming doctoral thesis).

Figure 4 :

 4 Figure 4: Proportion of whole (left) and archaeometrically-studied (right) assemblages by typological classification.

  3.2 X-ray fluorescence (XRF) XRF was used for the OM samples' bulk elemental composition of major, minor and (some) trace elements, conducted at the Laboratoire Archéomatériaux et Prévision de l'Altération (LAPA-IRAMAT/CEA) in Saclay, France. XRF data were acquired using a NITON XL 3t GOLDD+ portable XRF analyser in 'laboratory mode' (fixed stand), with a max 40 kV accelerating voltage in the 'alloys' mode. Accuracy and precision were assessed with eleven Certified Reference Materials (CRMs): B10, B12, B31, UZ 52-3, B21 and L 20-1 from the Centre de Development des Industries de Mise en Forme desMatériaux, France, from the Bureau of Analyzed Samples Ltd., England and 500, C1123 and 1275 from the National Institute for Standards and Technology (NIST, Table

3. 4

 4 Multi Collector -Inductively Coupled Plasma -Mass Spectrometer (MC-ICP-MS) Lead isotope analysis (LIA) was performed at the Service d'Analyse des Roches et des Minéraux of the Centre for Petrographic and Geochemical Research (SARM-CRPG) in Nancy,

Figure 5 :

 5 Figure 5: (top row, left to right), DS11 x 10 ppl showing intergranular corrosion and faster-cooled as-cast structure, DS14 x 10 ppl showing elemental segregation, lead inclusions (black areas) and an δ tin-rich phase (light blue) DS20 x 10 ppl showing intergranular corrosion and slower-cooled dendritic as-cast structure, (bottom row, left to right), DS2 x 20 ppl after etching, showing porosity, intergranular corrosion, elemental segregation and lead[ ?] inclusions, DS10 x 50 ppl showing copper sulphide inclusions (grey), an δ tin-rich phase (light blue) and faster-cooled structure, DS7 x 400 SEM BSE showing intergranular corrosion, elemental segregation, an α+δ eutectoid (light grey) and lead inclusions (white).

Figure 6 :

 6 Figure 6: Major alloy classes for studied samples across all sites.

Figure 7 :

 7 Figure 7: Variation of tin content in wt. %.

Figure 8 :

 8 Figure 8: Variation of lead content in wt. %.

Figure 9 :

 9 Figure 9: Proportion of 'Alloy-Types' for the miniature drums.

Figure 10 :

 10 Figure 10: LI ratios seen for the study assemblage alone, labelled by Alloy-Type.

Figure 12 :

 12 Figure 12: Present study LI data and available LI data for Thai lead minerals (TLM, courtesy V.C. Pigott).

Figure 13 :

 13 Figure13: LI ratios for leaded (>1 wt.%) copper-base and lead artefacts in the published SEALIP/BROGLASEA database.

Table 1 :

 1 Nomenclature, context and metric data for the archaeometrically studied assemblages from Đông Sơn, Lãng Ngâm and Thiệu Dương.

Table 2 :

 2 CRM results. The table presents raw data from XRF and SEM-EDS analyses.

Table 3 :

 3 Elemental compositional data for Đông Sơn, Lãng Ngâm and Thiệu Dương samples. Major alloying components (Sn, Pb, Cu) are highlighted, as are those indicative of corrosion and thus intepretative caution. O percentage, not measured by stoichiometry, are also an indicator of corrosion degree. Detection limit is 0.5 wt. % for SEM-EDS and 700 ppm for XRF (varying in function of the element, note that light elements detection is not accurate with XRF).

Table 4 :

 4 Raw lead isotope ratios for the studied artefacts.

wt. % wt. % wt.% wt. % wt. % wt. % wt. % wt.% wt. % wt. % wt.% wt. % wt. % wt. % wt. % wt.

	Sb	Sn	Bi	Pb	Zn	Cu	Ni	Co Fe	Mn Al	S
	B12 pXRF Sample	0.12 10.00 nd Site	0.20 0.66 85.20 2.79 nd 208 Pb/ 206 Pb	0.17 0.24 nd nd 207 Pb/ 206 Pb	208 Pb/ 204 Pb	207 Pb/ 204 Pb	206 Pb/ 204 Pb	Alloy-Type
	B12 SEM-EDS B12 CRMs value SEALIP/VN/DS/1 51.13-4 pXRF 51.13-4 SEM-EDS SAMPLE SEALIP/VN/DS/2 SEALIP/VN/DS/3 51.13-4 CRMs value Đông Sơn SEALIP/VN/DS/4 71.32-4 pXRF SEALIP/VN/DS/1 nd Đông Sơn 0.12 9.57 0.00 0.20 0.61 85.65 2.63 0.00 0.16 0.24 0.13 0.00 9.5 nd nd 0.9 85.0 3.0 nd nd nd nd nd 2.109 ± 0.00007 0.854 ± 0.00002 nd 0.30 nd 0.11 0.4 91.00 nd nd 1.95 0.90 4.95 nd nd nd nd nd 0.7 87.7 nd nd O Sb Sn Ag Bi Pb As Cu Ni Fe 38.899 Cr wt. % % ± 0.0076 15.754 ± 0.0030 V Ti Al S P Si Đông Sơn 2.087 ± 0.00009 0.837 ± 0.00001 39.267 ± 0.0032 15.759 ± 0.0010 Đông Sơn 2.108 ± 0.00020 0.853 ± 0.00003 38.832 ± 0.0084 15.720 ± 0.0035 2.0 1.0 8.0 nd Đông Sơn 2.112 ± 0.00018 0.852 ± 0.00004 38.941 ± 0.0126 15.724 ± 0.0048 0.00 0.27 0.00 0.00 0.34 88.79 0.06 0.00 1.81 0.90 7.30 0.00 0.25 6.40 nd 4.30 7.00 80.50 0.78 nd 0.06 2.00 0.00 0.00 6.00 0.00 89.50 0.02 0.06 0.00 0.00 0.00 1.00 0.00 0.00 1.00 SEALIP/VN/DS/5 Đông Sơn 2.095 ± 0.00016 0.845 ± 0.00002 39.016 ± 0.0064 15.748 ± 0.0020 0.40 nd nd nd 71.32-4 SEM-EDS nd 6.5 nd 3.0 7.0 82.0 0.8 nd 0.4 nd nd nd 71.32-4 CRMs value 0.26 6.46 0.05 4.43 6.52 80.48 0.70 0.00 0.35 0.05 0.12 0.00 C1123 pXRF nd nd nd nd nd 97.40 nd 2.49 nd nd nd nd C1123 SEM-EDS nd nd nd nd nd 96.5 nd 3.5 nd nd nd nd C1123 CRMs value 0.00 0.01 0.00 0.00 0.01 97.40 0.01 2.30 0.00 0.00 0.02 0.00 L-20-1 pXRF nd 0.54 nd 0.30 14.35 84.15 0.25 nd nd 0.15 nd nd L-20-1 SEM-EDS nd 0.5 nd nd 14.5 84.0 nd nd nd nd nd nd L-20-1 CRMs value 0.00 0.49 0.00 0.27 13.33 85.20 0.22 0.00 0.04 0.13 0.07 0.00 B31 pXRF 0.50 7.95 nd 10.60 0.84 79.40 0.55 nd nd nd nd nd B31 SEM-EDS 1.8 8.0 nd 9.9 1.1 78.6 0.5 nd nd nd nd nd B31 CRMs value 0.48 7.70 0.00 11.79 0.82 78.55 0.49 0.00 0.02 0.00 0.04 0.03 UZ-52-3 pXRF 0.08 0.99 nd 0.10 18.00 80.30 0.10 nd 0.34 nd nd nd UZ-52-3 SEM-EDS nd 1.0 nd nd 18.5 80.5 nd nd nd nd nd nd UZ-52-3 CRMs value 0.08 1.06 0.00 0.11 17.00 81.08 0.08 0.00 0.31 0.00 0.00 0.00 B21 pXRF 0.19 5.35 nd 3.75 6.53 82.20 1.35 nd 0.30 nd nd nd B21 SEM-EDS nd 5.0 nd 4.0 7.0 82.0 1.0 nd nd nd nd nd B21 CRMs value 0.18 5.13 0.00 3.79 6.22 83.00 1.21 0.00 0.29 0.00 0.14 0.05 SRM1275 pXRF nd nd nd nd nd 86.90 10.70 nd 1.63 0.39 nd nd SRM1275 SEM-EDS nd nd nd nd nd 87.9 10.1 nd 1.5 0.5 nd nd SRM1275 CRMs value 0.00 0.01 0.00 0.01 0.09 88.20 9.76 0.02 1.46 0.42 0.00 0.00 SRM-500 pXRF nd nd nd nd 0.10 99.70 0.08 nd nd nd nd nd SRM-500 SEM-EDS nd nd nd nd 0.5 99.5 nd nd nd nd nd nd 6.5 1.5 3.0 89.0 SEALIP/VN/DS/2 1.00 8.00 0.24 0.00 11.00 0.00 77.00 0.00 0.10 0.00 0.00 0.00 1.50 0.00 0.00 0.40 SEALIP/VN/DS/6 Đông Sơn 2.107 ± 0.00011 0.851 ± 0.00001 38.721 ± 0.0042 15.637 ± 0.0014 6.4 2.5 7.0 16.0 68.0 SEALIP/VN/DS/7 Đông Sơn 2.094 ± 0.00010 0.844 ± 0.00002 39.038 ± 0.0042 15.737 ± 0.0014 SEALIP/VN/DS/3 0.00 8.00 0.00 0.00 7.50 0.00 77.50 0.00 0.33 0.00 0.04 0.00 3.45 0.00 0.50 2.00 SEALIP/VN/DS/8 Đông Sơn 2.115 ± 0.00012 0.852 ± 0.00002 38.976 ± 0.0041 15.703 ± 0.0013 5.5 8.0 2.0 84.5 SEALIP/VN/DS/9 Đông Sơn 2.104 ± 0.00023 0.850 ± 0.00002 38.958 ± 0.0094 15.743 ± 0.0031 SEALIP/VN/DS/4 0.00 0.00 0.00 0.00 2.46 0.00 88.00 0.00 0.50 0.00 0.00 0.00 2.54 0.00 2.00 4.00 SEALIP/VN/DS/10 Đông Sơn 2.110 ± 0.00027 0.850 ± 0.00002 38.955 ± 0.0108 15.698 ± 0.0034 7.0 0.0 1.4 91.5 SEALIP/VN/DS/11 Đông Sơn 2.105 ± 0.00013 0.851 ± 0.00004 38.938 ± 0.0095 15.739 ± 0.0036 SEALIP/VN/DS/5 0.28 14.50 0.00 0.00 18.00 0.00 63.00 0.00 0.12 0.00 0.00 0.00 2.00 0.00 0.41 1.00 SEALIP/VN/DS/12 Đông Sơn 2.107 ± 0.00025 0.853 ± 0.00004 38.922 ± 0.0135 15.762 ± 0.0048 8.0 7.0 39.9 45.0 SEALIP/VN/DS/13 Đông Sơn 2.108 ± 0.00019 0.854 ± 0.00006 38.888 ± 0.0168 15.748 ± 0.0067 SEALIP/VN/DS/6 0.00 0.16 0.00 0.02 2.00 0.27 91.50 0.01 0.13 0.00 0.00 0.00 2.50 0.00 0.32 3.02 SEALIP/VN/DS/14 Đông Sơn 2.096 ± 0.00015 0.845 ± 0.00001 39.014 ± 0.0055 15.735 ± 0.0017 2.0 0.0 1.0 97.0 SEALIP/VN/DS/15 Đông Sơn 2.105 ± 0.00022 0.852 ± 0.00004 38.878 ± 0.0143 15.746 ± 0.0053 SEALIP/VN/DS/7 0.11 17.00 0.00 0.14 11.00 0.00 67.00 0.05 0.34 0.00 0.00 0.00 2.70 0.00 0.00 1.00 SEALIP/VN/DS/16 Đông Sơn 2.103 ± 0.00020 0.851 ± 0.00008 38.875 ± 0.0248 15.731 ± 0.0099 7.0 16.0 15.0 62.0 SEALIP/VN/DS/17 Đông Sơn 2.094 ± 0.00016 0.844 ± 0.00002 39.042 ± 0.0054 15.738 ± 0.0018 SEALIP/VN/DS/8 0.09 6.45 0.00 0.10 11.00 0.58 75.50 0.01 0.20 0.00 0.00 0.00 1.50 0.00 0.82 3.60 SEALIP/VN/DS/18 Đông Sơn 2.105 ± 0.00015 0.852 ± 0.00003 38.876 ± 0.0062 15.739 ± 0.0023 10.0 3.5 7.0 78.5 SEALIP/VN/DS/19 Đông Sơn 2.111 ± 0.00013 0.857 ± 0.00002 38.892 ± 0.0055 15.780 ± 0.0020 SEALIP/VN/DS/9 0.92 2.60 1.84 1.18 1.24 1.23 86.14 0.00 0.10 0.35 0.60 1.58 0.00 0.00 0.19 0.95 SEALIP/VN/DS/20 Đông Sơn 2.081 ± 0.00022 0.831 ± 0.00011 39.180 ± 0.0307 15.637 ± 0.0125 45.0 1.0 2.0 0.4 25.5 4.0 SEALIP/VN/LN/1 Lãng Ngâm 2.109 ± 0.00012 0.851 ± 0.00002 39.058 ± 0.0050 15.756 ± 0.0016 8.0 SEM-EDS 18.440 Analysis 18.816 18.425 18.440 XRF 18.625 SEM-EDS XRF 18.378 18.638 SEM-EDS XRF 18.424 18.517 SEM-EDS XRF 18.461 18.496 SEM-EDS XRF 18.470 18.449 SEM-EDS XRF 18.613 18.473 SEM-EDS XRF 18.484 18.641 SEM-EDS XRF 18.465 18.423 SEM-EDS XRF 18.833 18.522 SEALIP/VN/DS/10 0.02 15.40 0.00 0.00 0.08 0.04 83.50 0.00 0.50 0.00 0.00 0.18 0.00 0.06 0.02 0.24 XRF SEALIP/VN/THD/1 Thiệu Dương 2.067 ± 0.00017 0.819 ± 0.00009 39.466 ± 0.0399 15.646 ± 0.0162 19.096 4.0 14.0 0.0 82.0 SEALIP/VN/THD/2 Thiệu Dương 2.110 ± 0.00025 0.852 ± 0.00007 38.847 ± 0.0253 15.687 ± 0.0105 18.411 SEM-EDS SEALIP/VN/DS/11 0.07 3.00 0.00 0.00 1.70 0.18 94.50 0.03 0.07 0.00 0.00 0.00 0.00 0.00 0.00 0.30 XRF SEALIP/VN/THD/3 Thiệu Dương 2.110 ± 0.00013 0.856 ± 0.00005 38.891 ± 0.0107 15.768 ± 0.0038 18.428	± (1 wt.% threshold) 0.0033 Alloy ± 0.0010 ± 0.0039 ± 0.0050 leaded bronze ± 0.0018 leaded bronze ± 0.0015 ± 0.0016 leaded bronze ± 0.0013 ± 0.0029 leaded copper ± 0.0030 ± 0.0042 leaded bronze ± 0.0042 ± 0.0077 leaded copper ± 0.0015 ± 0.0058 leaded bronze ± 0.0116 ± 0.0018 leaded bronze ± 0.0028 ± 0.0022 leaded bronze ± 0.0173 ± 0.0019 bronze ± 0.0189 ± 0.0125 leaded bronze ± 0.0046	LB3 LB1 Corrosion LB1 LC4 Medium LB1 Medium LCNC LB1 Low LB2 LB3 High BR LBNC High LC3 C3 Low LB1 LC3 Medium LC3 LB1 High LBNC LBNC High B1 LB1 Low B1 B5 Medium not classified Type Type 3 Type 1 Type 1 Type 4 Type 1 not classified Type 1 Type 2 Type 3 remarkable LCNC	Alloy-Type LB3 LB1 LB1 LC4 LB1 LCNC LB1 LB2 LB3 BR LBNC	Artefact miniature drum miniature drum miniature drum miniature drum miniature drum miniature drum miniature tympanum miniature drum miniature drum miniature drum miniature drum
	SRM-500 CRMs value B10 pXRF B10 SEM-EDS SEALIP/VN/DS/12 0.01 0.00 0.00 0.01 0.01 99.70 0.06 0.00 0.00 0.00 0.00 0.00 1.15 7.20 nd 4.14 2.95 83.20 1.10 nd 6.0 3.0 1.0 90.0 0.18 nd nd nd 2.0 6.5 nd 3.5 3.0 83.0 0.05 0.20 0.00 0.01 1.00 0.23 97.59 0.04 0.00 0.00 0.00 0.00 0.00 0.00 0.10 0.40 1.0 nd nd nd nd nd B10 CRMs value 4.00 0.0 1.0 95.0 1.14 6.95 0.00 4.07 2.75 83.65 1.01 0.00 0.17 0.00 0.21 0.00 SEALIP/VN/DS/13 0.13 0.15 0.00 0.02 0.60 0.63 97.00 0.07 0.06 0.01 0.06 0.06 0.00 0.00 0.03 0.66	SEM-EDS XRF SEM-EDS XRF	leaded copper copper	Low Low	Type 3 Type 3	LC3 C3	miniature drum miniature drum
			4.5		0.2			0.3			95.0	SEM-EDS
	SEALIP/VN/DS/14		0.07 10.00 0.00 0.02 13.45 0.00 76.00 0.01 0.00 0.00 0.00 0.10 0.00 0.00 0.00 0.00	XRF	leaded bronze	Medium	Type 1	LB1	miniature drum
			13.0		14.5			13.5			58.5	SEM-EDS
	SEALIP/VN/DS/15		0.00 0.02 0.00 0.01 2.00 0.13 97.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.62	XRF	leaded copper	Low	Type 3	LC3	miniature drum
			4.0		0.0			1.0			95.0	SEM-EDS
	SEALIP/VN/DS/16		0.17 0.10 0.00 0.00 1.00 0.02 93.48 0.00 0.01 0.00 0.00 0.03 1.75 0.00 0.12 1.73	XRF	leaded copper	Low	Type 3	LC3	miniature drum
			2.0		0.2			1.0			96.0	SEM-EDS
	SEALIP/VN/DS/17		0.16 19.66 0.00 0.16 14.45 0.00 65.00 0.04 0.18 0.00 0.00 0.20 0.00 0.00 0.00 0.00	XRF	leaded bronze	Low	Type 1	LB1	miniature drum
			3.5		14.0			11.0 0.5 71.0	SEM-EDS
	SEALIP/VN/DS/18		0.02 19.00 0.00 0.01 2.66 0.00 73.95 0.00 0.64 0.00 0.00 0.00 0.66 0.00 0.19 2.50	XRF	leaded bronze	Medium not classified	LBNC	miniature drum
			5.5		14.5			3.0			75.0	0.5	1.0 SEM-EDS
	SEALIP/VN/DS/19		0.11 1.50 0.00 0.00 2.50 0.11 91.00 0.00 0.01 0.01 0.02 0.04 0.00 0.00 0.13 4.57	XRF	leaded bronze	High	not classified	LBNC	situla
			16.0		1.0			1.0			82.0	0.5 SEM-EDS
	SEALIP/VN/DS/20		0.05 16.50 0.00 0.00 0.08 0.08 82.00 0.03 0.21 0.00 0.00 0.09 0.00 0.24 0.16 0.34	XRF	bronze	Medium	Type 1	B1	medium drum
			3.5		12.5			0.0			83.5	0.5	SEM-EDS
	Lãng Ngâm
	SEALIP/VN/LN/1			0.14 15.00 0.00 0.00 11.00 0.00 72.20 0.00 0.60 0.02 0.08 0.27 0.00 0.00 0.00 0.00	XRF	leaded bronze	Type 1	LB1	miniature drum
			2.0		13.0			13.5			71.0	0.5	SEM-EDS
	Thiệu Dương
	SEALIP/VN/THD/1		0.00 20.40		0.00 0.15 0.07 73.50 0.05 3.00 0.00 0.00 0.00 0.00 0.35 1.00 1.16	XRF	bronze	Medium	Type 1	B1	miniature drum
			4.0		13.5			0.0			80.0	1.0	0.5	SEM-EDS
	SEALIP/VN/THD/2		0.00 21.00 0.00 0.00 0.38 0.02 74.50 0.00 0.24 0.00 0.00 0.00 0.00 0.00 0.36 2.00	XRF	bronze	High	Type 5	B5	miniature drum
			19.0		18.0			0.0			61.5	1.0	0.5 SEM-EDS
	SEALIP/VN/THD/3		0.60 0.49 0.00 0.00 1.30 0.00 95.50 0.00 0.01 0.10 0.25 0.65 0.00 0.00 0.05 0.00	XRF	leaded copper	Medium not classified	LCNC	miniature drum
			2.5		0.0			1.5			96.0	SEM-EDS
	No context
	HNM-lsb2752			0.10 5.05 0.16 0.00 4.10 0.16 89.50 0.04 1.00 0.00 0.00 0.00 0.00 0.00 0.00 0.07	XRF	leaded bronze	Medium	Type 5	LB5	miniature drum
			5.5		4.0			5.0		0.4 84.0	1.0	SEM-EDS
	HNM-lsb7255			0.12 12.00 0.00 0.06 6.00 0.27 80.45 0.01 0.30 0.03 0.00 0.13 0.00 0.00 0.00 0.00	XRF	leaded bronze	Medium	Type 1	LB1	miniature drum
			5.5		11.0			9.5		1.0 73.0	SEM-EDS

Acknowledgments

The lead author's doctoral study was financed by a grant from the French Ecole Pratique des Hautes Etudes, Paris Sciences & Lettres (EPHE-PSL). The laboratory analyses presented here were financed by the French National Research project "Bronze and Glass as Cultural Catalysts and Tracers in Early Southeast Asia 2016-2020" (BROGLASEA, ANR-16-CE27-0011-01) directed by T.O. Pryce. We offer our warm thanks to the Vietnamese museum curators, archaeologists and the relevant state authorities who provided us study and sampling access as well as export permits, so as to reviewers, who carefully read this paper in order to improve it.