Methodological study on single grain OSL dating of mortars: Comparison of five reference archaeological sites

List of studied monuments with corresponding historical periods, reference date intervals, reference dating methods, mortar function in masonry and sample numbers. For more details about the list of mortar samples, the reader is referred to Urbanová et al. (2016) for Antibes, to Urbanová et al. (2015) for Palais-Gallien and to Urbanová and Guibert (2017) for Saint Seurin. For more details about reference dates, the reader is referred to Lanos and Dufresne (2013) for Antibes, to Hourcade (2013) and Lanos and Dufresne (2013) for Palais-Gallien, to Michel (2012) for Saint Seurin, to Hourcade and Maurin (2013) and Lanos and Dufresne (2013) for Chassenon, to Fischer (2008) for Basel and to Hueglin (2011) for mortar mixers.

Site	Historical period	Reference date interval	Reference dating method	Mortar function	Sample number
					BDX 16045
					BDX 16046
Antibes	Gallo-Roman	[9 BC, 72 AD]	Archaeomagnetism (bricks)	Mortar binding stones	BDX 16047
		TPQ*: [60 AD, 100 AD]	Archaeology		BDX 16048
					BDX 16049

Chassenon	Gallo-Roman			Boarding mortar	BDX 15628
		[82 AD, 178 AD]	Archaeomagnetism (bricks)	Mortar binding stones	BDX 15636
		[90 AD, 170 AD]	Archaeology	Mortar binding stones	BDX 15638
				Mortar binding stones	BDX 15639

Palais-Gallien	Gallo-Roman			Mortar binding bricks	BDX 15541
		[68 AD, 150 AD]	Archaeomagnetism (bricks)	Mortar binding bricks	BDX 15542
		[90 AD, 170 AD]	Archaeology	Foundation mortar	BDX 15543
				Foundation mortar	BDX 15544

		Posterior to BDX 16493 TPQ: 1100 AD	Archaeology	Filling mortar (floor)	BDX 16492

	Late Antiquity & Early Middle Ages crypt	Posterior to BDX 16496 TPQ: 1100 AD	Archaeology	Filling mortar (floor)	BDX 16493
	Late Antiquity & Early Middle Ages crypt
				Ground mortar	BDX 16496

		[305 AD, 562 AD] TPQ*: [658 AD, 783 AD]	TL and OSL (bricks) Radiocarbon (charcoal)	Ground mortar	BDX 16498
		[305 AD, 562 AD] TPQ*: [658 AD, 783 AD]	TL and OSL (bricks) Radiocarbon (charcoal)
St Seurin				Ground mortar (floor)	BDX 16500

					BDX 16592
	Romanesque apse	[810 AD, 910 AD]	Historical sources	Mortar binding ashlars	BDX 16593
					BDX 16594

					BDX 16586
	Gothic chapel	[570 AD]	Historical sources	Mortar binding ashlars	BDX 16587
					BDX 16591

	Gallo-Roman	[270 AD, 350 AD]	Historical sources	Ground mortar (hypocaust)	BDX 16304

	Late Antiquity & Early Middle Ages	[300 AD, 800 AD]	Archaeology	Mortar binding stones	BDX 16293
	Late Antiquity & Early Middle Ages	[300 AD, 800 AD]	Archaeology	Mortar binding stones	BDX 16299

Basel	Carolingian	[790 AD, 890 AD]	Archaeology	Mortar binding stones	BDX 16301
Basel	Carolingian	[790 AD, 890 AD]	Archaeology	Mortar binding stones	BDX 16303

	Ottonian	[890 AD, 990 AD]	Archaeology	Mortar binding stones	BDX 16288
	Ottonian	[890 AD, 990 AD]	Archaeology	Mortar binding stones	BDX 16294

	Romanesque	[1100 AD, 1200 AD]	Archaeology	Mortar binding stones	BDX 16295

Basel	Romanesque	[936 AD, 1018 AD]	Radiocarbon (charcoal)	Mortar from mortar mixer	BDX 16306

Müstair	Romanesque	958 AD	Historical sources	Mortar from mortar mixer	BDX 16308

Zurich	Romanesque	[853 AD, 874 AD]	Historical sources	Mortar from mortar mixer	BDX 16309

* terminus post quem

Table 2

Measurement parameters used for the determination of individual equivalent doses.

Site	Preheat (°C)	Cut-heat (°C)	Test dose (Gy)	Recovery dose (Gy)	Regeneration doses (Gy)
Grimaldi castle, Antibes	240	190	4.8	4.8	4.8, 9.6, 14.4, 19.2, 0, 4.8

Thermal baths of Chassenon	220	190	4.8	4.8	4.8, 9.6, 14.4, 19.2, 0, 4.8

Palais-Gallien, Bordeaux	240	190	4.8	4.8	4.8, 9.6, 14.4, 19.2, 0, 4.8

Basel cathedral, Basel	190	160	1.5	1.5	0.75, 1.5, 4.5, 10.5, 0, 0.75

Saint Seurin crypt, Bordeaux	190	160	3	3	1.5, 3, 6, 12, 0, 1.5

Saint Seurin apse/chapel, Bordeaux	190	160	1.5	1.5	0.75, 1.5, 4.5, 10.4, 0, 0.75

Mortar mixers (Basel, Müstair, Zurich)	190	160	3	3	1.5, 3, 6, 12, 0, 1.5

Table 3

Number of studied grains and proportions of luminescent and selected grains for all studied samples.

Sample	Analysed grains		Luminescent grains		Selected grains		Grains above L₄/ T₄*
Sample
	Nb	%	Nb	%	Nb	%	Nb
Grimaldi castle, Antibes

BDX 16045	4085	100	200	5.0	196	4.8	0
BDX 16046	3800	100	193	5.0	180	4.6	1
BDX 16047	3800	100	179	4.8	175	4.7	5
BDX 16048	3990	100	205	4.9	189	4.5	0
BDX 16049	4085	100	163	3.9	152	3.6	1

Thermal baths of Chassenon

BDX 15628		little quartz fraction 200-250 μm, no OSL signal
BDX 15636	3895	100	67	1.7	61	1.6	9
BDX 15638		little quartz fraction 200-250 μm, no OSL signal
BDX 16539

Palais-Gallien, Bordeaux

BDX 15541	2850	100	202	7.1	129	4.5	44
BDX 15542	1900	100	119	6.3	76	4.0	40
BDX 15543	4135	100	207	5.0	111	2.7	51
BDX 15544	4085	100	324	7.9	192	4.7	104

Saint Seurin crypt, Bordeaux

BDX 16492	3800	100	275	7.3	176	4.6	57
BDX 16493	3800	100	233	6.1	145	3.8	52
BDX 16496	1995	100	99	5.0	32	1.6	26
BDX 16498	3800	100	152	3.8	71	1.9	49
BDX 16500	3800	100	127	3.1	90	1.9	21

Saint Seurin, apse, Bordeaux

BDX 16592	3610	100	368	10.2	164	4.5	117
BDX 16593	3040	100	256	8.4	116	3.8	79
BDX 16594	3135	100	347	11.1	152	4.8	101

Saint Seurin, chapel, Bordeaux

BDX 16586	2280	100	116	5.0	50	2.2	33
BDX 16587	3325	100	175	5.4	49	1.5	32
BDX 16591	-	-	-	-	-	-

Basel cathedral (crypt)

BDX 16304	3800	100	116	3.1	106	2.8	6
BDX 16293		analyzed by multigrain, very little OSL signal
BDX 16299
BDX 16301	2000
BDX 16303	2000
BDX 16288	2000			no OSL signal
BDX 16294	2000
BDX 16295	2000

Mortar mixers

BDX 16306	2000
BDX 16308	2000			no OSL signal
BDX 16309	2000

* grains with the sensitivity-corrected natural signal (L_N/T_N) above the highest regenerated dose (L₄/T₄). The equivalent dose estimation of these grains is performed by the extrapolation of the exponential growth curve.

SG-OSL decay curve of well bleached (a) and poorly bleached (b) grain. (c) LM-OSL test of the sample BDX 15541 performed by the multi-grain technique corresponding to an average signal of the mixture of poorly bleached and well bleached grains.

Histograms (a-f) show the distributions of individual equivalent doses from SG-OSL measurements.

Distributions of relative errors related to ED distributions presented in the Fig. 2.

Table 4

Over-dispersion values (OD) obtained by using Central age model (Galbraith et al., 1999) from dose recovery experiments (DRT) and equivalent dose measurements (ED) and estimation of extrinsic variability calculated as the difference between OD ED and OD DRT.

Sample	OD DRT	OD ED	Extrinsic
Sample	(%)	(%)	variability (%)
Grimaldi castle, Antibes

BDX 16045	14 ± 2	31 ± 2	28 ± 4
BDX 16046	12 ± 2	31 ± 2	29 ± 4
BDX 16047	8 ± 2	43 ± 3	42 ± 4
BDX 16048	7 ± 2	27 ± 2	26 ± 4
BDX 16049	5 ± 2	36 ± 2	36 ± 4

Thermal baths of Chassenon

BDX 15636	5 ± 2	45 ± 5	45 ± 7

Palais-Gallien, Bordeaux

BDX 15541	13 ± 2	121 ± 8	120 ± 10
BDX 15542	5 ± 2	129 ± 8	129 ± 10
BDX 15543	16 ± 3	148 ± 10	147 ± 13
BDX 15544	8 ± 2	144 ± 8	144 ± 10

Saint Seurin crypt, Bordeaux

BDX 16492	14 ± 2	129 ± 7	128 ± 9
BDX 16493	8 ± 2	128 ± 8	128 ± 10
BDX 16496	12 ± 3	96 ± 13	95 ± 16
BDX 16498	15 ± 4	106 ± 9	105 ± 13
BDX 16500	16 ± 3	117 ± 9	116 ± 12

Saint Seurin, apse, Bordeaux

BDX 16592	10 ± 3	136 ± 8	136 ± 11
BDX 16593	-	148 ± 10	-
BDX 16594	-	134 ± 8	-

Saint Seurin, chapel, Bordeaux

BDX 16586	7 ± 4	157 ± 16	157 ± 20
BDX 16587	-	148 ± 15	-

Basel cathedral (crypt)

BDX 16304	9 ± 2	68 ± 5	57 ± 14

Beta-autoradiography images of different mortar samples. The brightest spots correspond to the most intense beta emitters.

SEM-EDX carthography of potassium rich minerals in different mortar samples: (a) BDX 16048, (b) BDX 15636, (c) BDX 16304, (d) BDX 15541, (e) BDX 16496, (f) BDX 16493. The grey level corresponds to the number of X rays emitted by potassium detected by the instrument. Magnification: 60, pixel size: 0.03 mm.

Table 5

Results of the local analyses of potassium (K) content in thick sections of studied mortar samples, obtained by SEM-EDX. We introduce: n—number of analysis; K_min — the lowest measured value of K content; K_max — the highest measured value of K content; K_mean — arithmetic mean of K content for n measurements; σ_K — standard deviation of arithmetic mean K_mean for n measurements; σ_rel – relative standard deviation calculated as the ratio of σ_K to K_mean; K_gamma — K content determined by low background gamma spectrometry.

Sample	n	K_min	K_max	Kmean	σ	σ_rel	K_gamma	CaO
Sample	n	(%)	(%)	(%)	(%)	σ_rel	(%)	(%)
Antibes
BDX 16045	31	0.33	3.64	0.98	0.64	0.65	1.43	30
BDX 16046	_-	-	-	-	-	-	1.44	-
BDX 16047	_-	_-	_-	_-	_-	_-	1.88	_-
BDX 16048	22	1.13	2.86	1.69	0.44	0.26	1.94	-
BDX 16049	35	0.84	2.30	1.44	0.32	0.22	1.74	26

Chassenon
BDX 15636	17	1.48	3.56	2.71	0.55	0.20	2.86	33

Palais-Gallien
BDX 15541	29	0.12	1.10	0.53	0.27	0.50	0.85	26
BDX 15542	40	1.17	2.26	0.85	0.51	0.60	1.13	-
BDX 15543	33	0.04	1.09	0.43	0.27	0.62	0.80	29
BDX 15544	-	-	-	-	-	-	0.67	25

St Seurin
BDX 16492	13	0.11	1.11	0.59	0.41	0.58	0.43	22
BDX 16493	51	0.03	1.11	0.30	0.23	0.78	0.47	26
BDX 16496	24	0.12	2.24	0.80	0.46	0.57	0.90	27
BDX 16498	56	0.07	2.58	0.83	0.66	0.80	0.87	23
BDX 16500	39	0.09	1.54	0.47	0.33	0.70	0.49	24

BDX 16592	-	-	-	-	-	-	0.60	54
BDX 16593	15	0.12	0.46	0.32	0.11	0.33	0.30	62
BDX 16594	-	-	-	-	-	-	0.30	56

BDX 16586	_-	_-	_-	_-	_-	_-	1.05	69
BDX 16587	9	0.68	1.93	1.17	0.38	0.33	1.03	62

Basel
BDX 16304	38	0.27	1.39	0.68	0.31	0.45	0.44	61

BDX 16293	-	-	-	-	-	-	0.44	79
BDX 16299	-	-	-	-	-	-	0.55	63

(a) Relation between the mean K content determined by low bacground gamma spectrometry and SEM-EDX analyses. (b) Standard deviation of the mean K content σ as the function of the mean K content determined by low background gamma spectrometry. (c) Relative variability of K content σ_relative calculated as the ratio of standard deviation σ to the mean K content. Relative variability of K content is more significant for mortars with lower K content. Calculation of archeological dose (paleodose) and age Given that the mortar samples are not older than 2000 years, we prefer to use the term “archeological dose” instead of paleodose in the following paragraphs.

Table 6

Evaluation of bleaching degree: expected archaeological dose, the lowest and the highest measured equivalent dose, the ratio between the expected dose and minimum dose R_min and between the maximum dose and the expected dose R_max and the over-dispersion.

Site	Sample	Expected dose	Min	Max	R_min	R_max	R_max/R_min	OD
Site	Sample	(Gy)	(Gy)	(Gy)	R_min	R_max	R_max/R_min	(%)
	BDX 16045	3.70	1.14	8.46	3	2	0.7	31
	BDX 16046	3.55	1.00	10.88	4	3	0.9	31
Antibes	BDX 16047	4.70	1.18	11.84	4	3	0.6	43
	BDX 16048	4.30	1.65	9.76	3	2	1.9	27
	BDX 16049	3.85	1.69	12.74	2	3	1.5	36

Chassenon	BDX 15636	12.65	4.74	28.38	3	2	0.8	45

	BDX 15541	2.87	1.78	187.20	2	65	40	121
Palais-Gallien	BDX 15542	3.29	1.60	163.27	2	50	24	129
Palais-Gallien	BDX 15543	2.70	1.84	270.51	1	100	68	148
	BDX 15544	2.49	1.35	267.46	2	107	58	144

	BDX 16492	1.26–1.94	1.09	79.62	1–2	32–54	14	129
	BDX 16493	1.09–1.82	1.06	91.92	1–2	51–84	29	128
	BDX 16496	4.09	3.57	179.62	1	44	38	96
	BDX 16498	4.78	2.90	188.61	2	39	24	106
St Seurin	BDX 16500	1.51–2.52	1.27	108.33	1–2	43–72	22	117
St Seurin
	BDX 16592	0.90	0.79	147.66	1	164	144	136
	BDX 16593	0.74	0.65	151.03	1	204	179	148
	BDX 16594	0.69	0.64	140.94	1	204	189	134

	BDX 16586	0.88–1.06	1.07	194.89	1	184–221	186	157
	BDX 16587	0.81–0.97	1.05	161.81	1	167–200	181	148

	BDX 16304	2.00–2.09	0.55	15.97	4	8	2	48

Bale	BDX 16293	1.30–1.84	0.41	4.71	3–4	3	0.6	49
	BDX 16299	1.56–2.20	1.06	6.21	1–2	3	1.4	47

Table 7

Recapitulative table of dating results for samples emitting SG-OSL signal.

Sample	Reference date (years)	Water contentI (%)	Annual dose (mGy/year)	Archeo doseII (Gy)	Nb of grainsIII	σ/aIV (%)	Date (years)
Grimaldi castle, Antibes

BDX 16045		5.0 ± 2.5	1.83 ± 0.07	3.85 ± 0.10 (CAM)	196	31	−86 ±100
BDX 16046		6.0 ± 3.0	1.72 ± 0.08	3.56 ± 0.09 (CAM)	180	31	−62 ±104
BDX 16047	31 ± 40	13.0 ± 6.5	2.29 ± 0.17	4.60 ± 0.16 (CAM)	175	43	16 ± 137
BDX 16048		10.0 ± 5.0	2.07 ± 0.13	3.66 ± 0.08 (CAM)	189	27	216 ± 110
BDX 16049		13.0 ± 6.5	1.92 ± 0.14	3.89 ± 0.13 (CAM)	152	36	183 ±156

Thermal baths of Chassenon

BDX 15636	130 ± 48	10.0 ± 5.0	6.76 ± 0.38	12.73 ± 0.77 (CAM)	61	45	131 ± 131

Palais-Gallien, Bordeaux

BDX 15541		10.0 ± 5.0	1.51 ± 0.07	3.07 ± 0.12 (IEU)	37	15	−18 ± 90
BDX 15542	109 ± 41	8.0 ± 4.0	1.73 ± 0.09	3.39 ± 0.21 (IEU)	26	25	55 ± 128
BDX 15543		8.0 ± 4.0	1.42 ± 0.05	2.91 ± 0.12 (IEU)	28	15	−41 ± 94
BDX 15544		12.0 ± 6.0	1.31 ± 0.07	2.51 ± 0.10 (IEU)	25	15	99 ± 86

Saint Seurin crypt, Bordeaux

BDX 16492	>450, <1000	7.0 ± 3.5	1.24 ± 0.03	1.73 ± 0.04 (IEU)	71	14	574 ± 68
BDX 16493	>450, <1000	7.0 ± 3.5	1.21 ± 0.05	1.81 ± 0.05 (IEU)	50	12	523 ± 71
BDX 16496	433 ±129	3.0 ± 1.5	2.56 ± 0.09	-	-	-	-
BDX 16498	433 ±129	3.0 ± 1.5	2.99 ± 0.09	-	-	-	-
BDX 16500	433 ±129	8.0 ± 4.0	1.68 ± 0.08	2.74 ± 0.13 (IEU)	56	30	386 ±107

Saint Seurin, apse, Bordeaux

BDX 16592		5.0 ± 2.5	1.29 ± 0.06	1.09 ± 0.06 (IEU)	15	10	1170 ± 58
BDX 16593	1150 ± 50	5.0 ± 2.5	1.00 ± 0.05	1.13 ± 0.06 (IEU)	16	10	945 ± 74
BDX 16594		5.0 ± 2.5	0.98 ± 0.04	1.00 ± 0.06 (IEU)	15	10	999 ± 71

Saint Seurin, chapel, Bordeaux

BDX 16586	1444	5.0 ± 2.5	1.76 ± 0.10	1.29 ± 0.09 (IEU)	5	7	1301 ± 59
BDX 16587	1444	5.0 ± 2.5	1.61 ± 0.09	1.20 ± 0.10 (IEU)	4	7	1271 ±68

Basel cathedral (crypt)

BDX 16304	310 ± 40	13.0 ± 6.5	1.20 ± 0.06	2.86 ± 0.15 (CAM)	100	49	−368 ±168
BDX 16293*	550 ± 250	-	1.07 ± 0.06	1.60 ± 0.15 (CAM)	29 discs	47	520 ±160
BDX 16299*	550 ± 250	-	1.28 ± 0.07	2.51 ± 0.21 (CAM)	34 discs	48	55 ± 196