Results are summarized in Table 1. Even though we recognise the arbitrary nature of establishing a threshold values system for defining the different types of ancient alloys, to better organize the collected data, the following scheme proposed by Gaudenzi Asinelli et al. has been adopted [16]:
Table 1
Elemental composition of the artefacts from the Almohad neighbourhood of Mārtulah (wt.%); n.d.: not detected.
ID | Function | Cu | Zn | Sn | Pb | Fe | As | Ag | Ni | Sb |
Brass |
AA-01-02 | casket ornament | 91.90 | 4.95 | 1.40 | 0.75 | 0.30 | 0.46 | 0.07 | 0.02 | 0.15 |
AA-01-04 | casket ornament | 90.30 | 6.60 | 1.60 | 0.93 | 0.07 | 0.20 | 0.09 | 0.01 | 0.20 |
AA-01-13 | casket ornament | 86.75 | 12.40 | 0.48 | 0.08 | 0.19 | 0.10 | n.d. | n.d. | n.d. |
AA-01-14 | casket ornament | 89.35 | 8.35 | 0.90 | 0.40 | 0.35 | 0.40 | 0.09 | 0.01 | 0.15 |
AA-01-16 | casket ornament | 91.00 | 7.20 | 0.33 | 0.17 | 0.30 | 0.90 | 0.06 | 0.01 | 0.03 |
AA-01-17 | casket ornament | 89.30 | 8.75 | 1.20 | 0.22 | 0.02 | 0.42 | 0.09 | n.d. | n.d. |
AA-01-20 | casket ornament | 88.70 | 8.45 | 0.50 | 0.90 | 0.30 | 1.15 | n.d. | n.d. | n.d. |
AA-02-25 | casket ornament | 86.45 | 10.40 | 0.60 | 0.95 | 0.32 | 0.80 | 0.48 | n.d. | n.d. |
AA-02-26 | casket ornament | 86.91 | 10.34 | 0.91 | 1.15 | 0.22 | 0.15 | 0.32 | n.d. | n.d. |
AA-02-27 | casket ornament | 88.12 | 7.90 | 1.40 | 1.55 | 0.25 | 0.23 | 0.26 | 0.02 | 0.27 |
AA-02-28 | casket ornament | 93.05 | 4.62 | 0.70 | 0.75 | 0.29 | 0.15 | 0.29 | n.d. | 0.15 |
AA-02-29 | casket ornament | 77.31 | 22.37 | n.d. | 0.10 | 0.02 | 0.13 | n.d. | 0.07 | n.d. |
AA-02-30 | casket ornament | 83.92 | 14.52 | n.d. | 1.10 | 0.26 | 0.20 | n.d. | n.d. | n.d. |
AA-02-32 | casket ornament | 83.56 | 14.74 | 1.10 | 0.15 | 0.23 | 0.20 | n.d. | 0.02 | n.d. |
AA-02-33 | casket ornament | 78.31 | 20.30 | 1.10 | 0.05 | 0.03 | 0.12 | 0.06 | 0.03 | n.d. |
AA-02-36 | casket ornament | 86.15 | 12.07 | 1.25 | 0.30 | 0.10 | 0.13 | n.d. | n.d. | n.d. |
AA-02-37 | casket ornament | 86.55 | 10.20 | 1.70 | 1.02 | 0.10 | 0.19 | 0.07 | 0.02 | 0.15 |
AA-02-46 | casket ornament | 90.46 | 6.52 | 1.37 | 0.95 | 0.20 | 0.24 | 0.07 | 0.02 | 0.17 |
AA-02-54 | casket ornament | 88.80 | 9.95 | n.d. | 0.15 | 0.08 | 0.70 | 0.11 | 0.17 | 0.04 |
AA-03-62 | casket ornament | 81.93 | 14.11 | 1.40 | 1.35 | 0.11 | 0.90 | 0.20 | n.d. | n.d. |
AN-01-36 | ring | 87.51 | 10.50 | 0.40 | 0.55 | 0.27 | 0.70 | 0.07 | n.d. | n.d. |
AR-01-35 | ring | 85.22 | 12.07 | 1.38 | 0.80 | 0.26 | 0.22 | n.d. | 0.05 | n.d. |
BC-01-05 | earring | 94.32 | 2.47 | 1.16 | 1.40 | 0.10 | 0.55 | n.d. | n.d. | n.d. |
BC-01-06 | earring | 91.04 | 7.07 | 0.70 | 0.40 | 0.05 | 0.66 | 0.08 | n.d. | n.d. |
BC-01-07 | earring | 93.41 | 4.75 | 0.65 | 0.60 | 0.06 | 0.15 | 0.14 | 0.01 | 0.23 |
BC-01-11 | earring | 89.79 | 7.98 | 1.35 | 0.21 | 0.03 | 0.55 | 0.09 | n.d. | n.d. |
BC-01-16 | earring | 88.53 | 9.41 | 1.05 | 0.45 | 0.10 | 0.31 | 0.15 | n.d. | n.d. |
BC-01-17 | earring | 82.88 | 14.12 | 1.35 | 0.65 | 0.20 | 0.80 | n.d. | n.d. | n.d. |
BC-01-18 | earring | 85.47 | 13.08 | 0.85 | 0.15 | 0.07 | 0.25 | 0.13 | n.d. | n.d. |
BC-01-19 | earring | 88.67 | 9.23 | 0.65 | 0.22 | 0.06 | 1.10 | 0.07 | n.d. | n.d. |
BC-01-21 | earring | 82.98 | 14.72 | 1.20 | 0.25 | 0.05 | 0.80 | n.d. | n.d. | n.d. |
BC-01-26 | earring | 86.96 | 11.55 | 0.75 | 0.10 | 0.06 | 0.50 | 0.08 | n.d. | n.d. |
BC-01-30 | earring | 92.38 | 4.98 | 1.16 | 0.95 | 0.12 | 0.40 | n.d. | 0.01 | n.d. |
BC-01-42 | earring | 88.27 | 8.71 | 0.90 | 0.48 | 0.14 | 1.50 | n.d. | n.d. | n.d. |
BC-01-46 | earring | 91.79 | 5.76 | 0.88 | 0.62 | 0.10 | 0.85 | n.d. | n.d. | n.d. |
BC-01-55 | earring | 88.69 | 7.73 | 1.85 | 0.85 | 0.20 | 0.40 | n.d. | 0.02 | 0.26 |
BC-01-61 | earring | 90.92 | 5.75 | 1.35 | 1.00 | 0.26 | 0.35 | 0.11 | 0.02 | 0.24 |
BC-01-62 | earring | 87.33 | 10.32 | 1.15 | 0.21 | 0.03 | 0.90 | 0.06 | n.d. | n.d. |
BC-01-66 | earring | 90.56 | 5.61 | 1.80 | 0.95 | 0.25 | 0.55 | 0.10 | n.d. | 0.18 |
BC-01-72 | earring | 86.07 | 11.43 | 1.30 | 0.50 | 0.02 | 0.60 | 0.07 | 0.01 | n.d. |
BC-01-76 | earring | 91.58 | 6.44 | 0.75 | 0.60 | 0.04 | 0.25 | 0.15 | 0.01 | 0.18 |
BC-01-89 | earring | 84.81 | 12.14 | 1.63 | 0.68 | 0.06 | 0.35 | 0.09 | 0.01 | 0.23 |
BC-03-101 | earring | 83.48 | 14.74 | 1.55 | 0.05 | 0.03 | 0.15 | n.d. | n.d. | n.d. |
BC-03-105 | earring | 88.35 | 9.00 | 1.25 | 0.60 | 0.20 | 0.30 | 0.09 | 0.01 | 0.20 |
BC-03-106 | earring | 87.23 | 9.42 | 1.70 | 1.05 | 0.05 | 0.30 | 0.07 | 0.01 | 0.17 |
BC-03-108 | earring | 83.68 | 14.32 | 0.87 | 0.38 | 0.10 | 0.65 | n.d. | n.d. | n.d. |
BC-03-109 | earring | 88.55 | 8.19 | 1.15 | 1.40 | 0.25 | 0.30 | 0.16 | n.d. | n.d. |
BC-03-115 | earring | 90.60 | 7.60 | 0.48 | 0.60 | 0.13 | 0.33 | 0.08 | 0.01 | 0.17 |
BC-03-97 | earring | 91.97 | 5.10 | 1.30 | 0.65 | 0.19 | 0.70 | 0.09 | n.d. | n.d. |
BC-03-98 | earring | 83.50 | 15.10 | 1.17 | 0.05 | 0.04 | 0.08 | n.d. | 0.06 | n.d. |
DV-02-44 | undetermined | 93.28 | 4.19 | 0.90 | 0.25 | 0.21 | 0.74 | 0.43 | n.d. | n.d. |
DV-02-75 | undetermined | 89.80 | 7.65 | 0.95 | 0.85 | 0.09 | 0.47 | 0.06 | 0.01 | 0.12 |
DV-02-80 | undetermined | 89.87 | 6.45 | 1.30 | 1.93 | 0.12 | 0.22 | n.d. | 0.01 | 0.10 |
DV-03-113 | sword sheath | 93.98 | 2.27 | 0.80 | 1.35 | 0.18 | 0.60 | 0.16 | 0.07 | 0.59 |
DV-03-86 | undetermined | 88.30 | 8.90 | 1.55 | 0.48 | 0.03 | 0.48 | 0.08 | 0.02 | 0.16 |
DV-03-89 | undetermined | 89.46 | 8.10 | 0.95 | 0.47 | 0.35 | 0.45 | 0.07 | 0.02 | 0.13 |
EC-01-05 | oil lamp stick | 87.86 | 11.65 | n.d. | 0.30 | 0.07 | 0.12 | n.d. | n.d. | n.d. |
EC-01-07 | oil lamp stick | 85.70 | 14.05 | n.d. | 0.10 | 0.07 | 0.03 | 0.05 | n.d. | n.d. |
EC-01-09 | oil lamp stick | 89.74 | 6.94 | 1.65 | 1.15 | 0.25 | 0.21 | 0.06 | n.d. | n.d. |
EC-01-12 | oil lamp stick | 85.54 | 12.43 | 0.10 | 1.07 | 0.20 | 0.47 | 0.14 | 0.05 | n.d. |
EC-01-15 | oil lamp stick | 88.13 | 10.67 | n.d. | 0.55 | 0.03 | 0.10 | 0.21 | 0.31 | n.d. |
EC-01-16 | oil lamp stick | 88.89 | 8.70 | 0.60 | 0.38 | 0.35 | 0.78 | 0.14 | 0.01 | 0.15 |
ES-01-01 | spatula | 85.69 | 13.70 | 0.01 | 0.50 | 0.03 | 0.07 | n.d. | n.d. | n.d. |
ES-01-06 | spatula | 92.77 | 5.18 | 0.30 | 0.54 | 0.14 | 0.90 | n.d. | 0.02 | 0.15 |
ES-01-08 | spatula | 91.43 | 4.77 | 1.38 | 0.95 | 0.87 | 0.31 | 0.26 | 0.03 | n.d. |
ES-01-11 | spatula | 94.88 | 2.52 | 0.49 | 0.43 | 0.16 | 1.30 | n.d. | 0.01 | 0.21 |
ES-01-12 | spatula | 87.94 | 7.33 | 2.02 | 1.55 | 0.21 | 0.58 | n.d. | 0.03 | 0.34 |
ES-01-20 | spatula | 89.03 | 8.07 | 0.85 | 0.77 | 0.20 | 0.71 | 0.14 | 0.05 | 0.18 |
ES-01-22 | spatula | 88.14 | 7.68 | 1.55 | 1.70 | 0.15 | 0.44 | 0.12 | n.d. | 0.22 |
ES-02-23 | spatula | 88.66 | 9.67 | 0.50 | 0.51 | 0.04 | 0.62 | n.d. | n.d. | n.d. |
ES-02-27 | spatula | 89.26 | 8.41 | 0.74 | 0.28 | 0.10 | 1.20 | n.d. | 0.01 | n.d. |
ES-02-29 | spatula | 85.99 | 10.63 | 1.40 | 1.10 | 0.15 | 0.40 | n.d. | 0.03 | 0.30 |
ES-02-30 | spatula | 88.77 | 7.63 | 0.83 | 1.80 | 0.12 | 0.40 | 0.20 | 0.03 | 0.22 |
ES-02-54 | spatula | 93.94 | 4.49 | 0.24 | 0.61 | 0.21 | 0.30 | 0.20 | 0.01 | n.d. |
PF-01-02 | spindle | 88.39 | 7.61 | 1.41 | 0.90 | 0.06 | 1.35 | 0.27 | 0.01 | n.d. |
PF-01-04 | spindle | 90.93 | 5.08 | 2.03 | 0.49 | 0.15 | 0.50 | 0.60 | 0.01 | 0.21 |
PF-01-06 | spindle | 90.36 | 7.90 | 0.38 | 0.62 | 0.20 | 0.14 | 0.15 | 0.04 | 0.21 |
PF-01-100 | spindle | 93.10 | 3.67 | 1.55 | 0.52 | 0.35 | 0.23 | 0.27 | 0.01 | 0.30 |
PF-01-104 | spindle | 89.45 | 8.20 | 0.61 | 0.66 | 0.40 | 0.40 | 0.11 | 0.01 | 0.16 |
PF-01-106 | spindle | 84.99 | 12.06 | 0.85 | 0.88 | 0.16 | 1.05 | n.d. | 0.01 | n.d. |
PF-01-107 | spindle | 85.23 | 14.08 | 0.03 | 0.32 | 0.13 | 0.14 | 0.07 | n.d. | n.d. |
PF-01-16 | spindle | 88.66 | 9.23 | 1.03 | 0.13 | 0.15 | 0.80 | n.d. | n.d. | n.d. |
PF-01-20 | spindle | 85.81 | 11.58 | 1.42 | 0.32 | 0.07 | 0.80 | n.d. | n.d. | n.d. |
PF-01-27 | spindle | 88.54 | 9.28 | 0.40 | 0.65 | 0.13 | 0.86 | 0.14 | n.d. | n.d. |
PF-01-32 | spindle | 80.91 | 15.48 | 1.90 | 0.40 | 0.16 | 1.15 | n.d. | n.d. | n.d. |
PF-01-33 | spindle | 91.05 | 6.67 | 0.60 | 0.20 | 0.05 | 1.35 | 0.08 | n.d. | n.d. |
PF-01-36 | spindle | 81.16 | 15.78 | 1.66 | 0.20 | 0.23 | 0.83 | 0.13 | 0.01 | n.d. |
PF-01-37 | spindle | 83.62 | 13.83 | 1.00 | 0.40 | 0.25 | 0.79 | 0.11 | n.d. | n.d. |
PF-01-47 | spindle | 93.09 | 4.90 | 0.70 | 0.79 | 0.28 | 0.11 | 0.13 | n.d. | n.d. |
PF-01-54 | spindle | 83.75 | 14.87 | 0.29 | 0.17 | 0.07 | 0.78 | n.d. | n.d. | 0.07 |
PF-01-65 | spindle | 87.95 | 9.26 | 1.20 | 0.32 | 0.04 | 1.15 | 0.07 | 0.01 | n.d. |
PF-01-77 | spindle | 84.43 | 11.90 | 1.45 | 1.70 | 0.18 | 0.30 | n.d. | 0.04 | n.d. |
PF-01-81 | spindle | 92.73 | 4.39 | 1.15 | 0.85 | 0.19 | 0.55 | 0.14 | n.d. | n.d. |
PF-01-85 | spindle | 89.42 | 6.98 | 0.83 | 0.88 | 0.58 | 1.20 | 0.10 | 0.01 | n.d. |
PF-02-114 | spindle | 94.92 | 2.68 | 0.56 | 1.50 | 0.09 | 0.25 | n.d. | n.d. | n.d. |
PF-02-122 | spindle | 79.28 | 19.83 | 0.11 | 0.42 | 0.08 | 0.28 | n.d. | n.d. | n.d. |
PF-02-129 | spindle | 88.29 | 8.70 | 1.65 | 0.84 | 0.24 | 0.16 | 0.12 | n.d. | n.d. |
PF-02-131 | spindle | 88.57 | 8.95 | 1.70 | 0.41 | 0.07 | 0.19 | 0.08 | 0.03 | n.d. |
PF-02-156 | spindle | 84.17 | 13.09 | 1.10 | 0.37 | 0.15 | 0.88 | 0.24 | n.d. | n.d. |
PF-02-179 | spindle | 91.47 | 6.86 | 0.88 | 0.43 | 0.03 | 0.14 | n.d. | 0.19 | n.d. |
PF-02-182 | spindle | 86.72 | 9.23 | 1.81 | 1.72 | 0.20 | 0.26 | n.d. | 0.06 | n.d. |
PF-02-183 | spindle | 88.63 | 9.67 | 0.63 | 0.22 | 0.10 | 0.67 | 0.08 | n.d. | n.d. |
PF-02-185 | spindle | 84.86 | 13.43 | 1.26 | 0.15 | 0.06 | 0.13 | 0.05 | 0.06 | n.d. |
PF-02-223 | spindle | 90.63 | 5.92 | 1.74 | 0.95 | 0.05 | 0.38 | 0.11 | 0.02 | 0.20 |
PF-02-231 | spindle | 87.98 | 8.25 | 2.06 | 1.03 | 0.10 | 0.14 | n.d. | 0.44 | n.d. |
PF-02-232 | spindle | 82.17 | 14.86 | 1.74 | 0.73 | 0.20 | 0.25 | n.d. | 0.05 | n.d. |
Leaded brass |
AA-02-56 | casket ornament | 71.20 | 14.75 | 1.75 | 10.90 | 0.32 | 0.42 | 0.20 | 0.02 | 0.44 |
BC-01-81 | earring | 85.07 | 9.78 | 0.12 | 3.70 | 0.13 | 1.05 | 0.15 | n.d. | n.d. |
BC-03-100 | earring | 86.64 | 8.63 | 1.30 | 2.30 | 0.55 | 0.30 | 0.09 | 0.01 | 0.18 |
BC-03-120 | earring | 90.50 | 4.10 | 0.40 | 3.75 | 0.20 | 0.70 | 0.35 | n.d. | n.d. |
DV-03-95 | undetermined | 86.88 | 3.06 | 1.71 | 6.50 | 0.58 | 0.45 | 0.13 | 0.15 | 0.54 |
EC-01-14 | oil lamp stick | 75.84 | 19.69 | 0.07 | 4.19 | 0.07 | 0.12 | n.d. | 0.02 | n.d. |
ES-01-10 | spatula | 89.85 | 2.10 | 1.25 | 6.20 | 0.08 | 0.52 | n.d. | n.d. | n.d. |
PF-01-31 | spindle | 74.97 | 20.58 | 1.10 | 2.20 | 0.14 | 0.52 | 0.18 | 0.03 | 0.28 |
PF-01-38 | spindle | 80.97 | 15.44 | 0.14 | 2.90 | 0.11 | 0.20 | 0.24 | n.d. | n.d. |
PF-01-44 | spindle | 92.88 | 2.24 | 1.14 | 2.85 | 0.04 | 0.25 | 0.21 | n.d. | 0.39 |
PF-02-130 | spindle | 85.54 | 5.83 | 1.93 | 5.74 | 0.40 | 0.36 | 0.20 | n.d. | n.d. |
PF-02-230 | spindle | 91.89 | 3.33 | 1.62 | 2.10 | 0.30 | 0.51 | 0.24 | 0.01 | n.d. |
Bronze |
BC-02-70 | earring | 94.99 | 0.08 | 4.25 | 0.40 | 0.06 | 0.20 | n.d. | 0.02 | n.d. |
DV-02-47 | undetermined | 91.32 | 0.15 | 5.41 | 1.16 | 0.25 | 0.14 | 1.56 | 0.01 | n.d. |
DV-02-64 | undetermined | 90.54 | 0.06 | 9.09 | n.d. | 0.11 | 0.14 | 0.06 | n.d. | n.d. |
PF-01-01 | spindle | 91.34 | 1.54 | 4.63 | 1.10 | 0.20 | 0.61 | 0.17 | n.d. | 0.41 |
PF-01-78 | spindle | 91.94 | 1.94 | 2.93 | 0.79 | 0.20 | 0.26 | 1.94 | n.d. | n.d. |
Ternary alloy |
AA-01-06 | casket ornament | 83.75 | 10.70 | 2.30 | 1.47 | 0.50 | 0.25 | 0.85 | 0.03 | 0.15 |
AA-01-08 | casket ornament | 84.40 | 11.00 | 3.00 | 1.05 | 0.15 | 0.17 | 0.10 | 0.03 | 0.10 |
AA-01-18 | casket ornament | 88.60 | 7.40 | 2.10 | 1.10 | 0.05 | 0.32 | 0.08 | 0.15 | 0.20 |
AA-02-49 | casket ornament | 87.92 | 7.76 | 3.40 | 0.34 | 0.50 | 0.08 | n.d. | n.d. | n.d. |
AA-03-79 | casket ornament | 84.52 | 10.39 | 3.30 | 1.40 | 0.17 | 0.20 | n.d. | 0.02 | n.d. |
AN-01-35 | ring | 88.52 | 7.48 | 2.64 | 0.50 | 0.05 | 0.55 | 0.08 | 0.01 | 0.17 |
BC-01-09 | earring | 91.40 | 5.60 | 1.95 | 0.57 | 0.06 | 0.15 | 0.10 | n.d. | 0.17 |
BC-01-12 | earring | 89.71 | 5.45 | 3.65 | 0.60 | 0.02 | 0.27 | 0.09 | n.d. | 0.21 |
BC-01-82 | earring | 90.13 | 4.81 | 2.41 | 1.25 | 0.50 | 0.90 | n.d. | n.d. | n.d. |
BC-03-116 | earring | 86.52 | 6.27 | 4.85 | 1.15 | 0.20 | 1.00 | n.d. | 0.01 | n.d. |
EC-01-06 | oil lamp stick | 87.76 | 8.35 | 2.35 | 0.90 | 0.07 | 0.32 | 0.11 | 0.01 | 0.13 |
EC-01-08 | oil lamp stick | 82.46 | 12.62 | 2.75 | 1.25 | 0.05 | 0.12 | 0.40 | n.d. | 0.35 |
ES-02-26 | spatula | 86.74 | 9.39 | 2.30 | 0.81 | 0.04 | 0.32 | 0.13 | n.d. | 0.27 |
ES-02-36 | spatula | 88.22 | 8.05 | 2.50 | 0.58 | 0.25 | 0.26 | 0.14 | n.d. | n.d. |
PF-01-03 | spindle | 89.18 | 6.13 | 2.82 | 0.78 | 0.15 | 0.59 | 0.10 | n.d. | 0.25 |
PF-01-05 | spindle | 91.77 | 4.23 | 2.25 | 0.86 | 0.14 | 0.37 | 0.37 | 0.01 | n.d. |
PF-01-11 | spindle | 86.88 | 11.59 | 0.43 | 0.25 | 0.12 | 0.72 | n.d. | 0.01 | n.d. |
PF-01-30 | spindle | 77.77 | 17.61 | 3.68 | 0.74 | 0.09 | 0.11 | n.d. | n.d. | n.d. |
PF-01-55 | spindle | 87.74 | 7.03 | 3.35 | 1.10 | 0.29 | 0.24 | 0.25 | n.d. | n.d. |
PF-01-99 | spindle | 90.06 | 4.15 | 3.80 | 1.25 | 0.15 | 0.18 | 0.12 | 0.02 | 0.27 |
PF-02-128 | spindle | 84.22 | 10.78 | 2.97 | 1.15 | 0.48 | 0.34 | n.d. | 0.06 | n.d. |
PF-02-161 | spindle | 84.89 | 11.74 | 2.19 | 0.75 | 0.15 | 0.26 | n.d. | 0.02 | n.d. |
PF-02-178 | spindle | 87.33 | 8.06 | 2.90 | 1.18 | 0.15 | 0.30 | n.d. | 0.08 | n.d. |
Leaded ternary alloy |
AA-01-21 | casket ornament | 88.10 | 3.70 | 3.05 | 4.00 | 0.50 | 0.37 | 0.09 | 0.02 | 0.17 |
AA-02-39 | casket ornament | 84.68 | 7.33 | 5.30 | 2.15 | 0.24 | 0.07 | 0.10 | 0.01 | 0.12 |
AR-01-53 | ring | 75.13 | 2.12 | 9.75 | 11.05 | 0.55 | 0.80 | n.d. | 0.05 | 0.55 |
BC-01-86 | earring | 68.74 | 18.08 | 6.25 | 6.30 | 0.09 | 0.30 | 0.21 | 0.03 | n.d. |
BC-03-118 | earring | 83.57 | 10.94 | 2.34 | 2.25 | 0.32 | 0.50 | n.d. | 0.08 | n.d. |
DV-01-31 | undetermined | 82.25 | 9.30 | 4.30 | 3.60 | 0.15 | 0.10 | 0.09 | 0.01 | 0.20 |
DV-02-63 | undetermined | 82.71 | 4.96 | 2.12 | 7.85 | 0.40 | 0.64 | 0.20 | 0.10 | 1.02 |
EC-01-01 | oil lamp stick | 85.62 | 8.73 | 2.12 | 2.75 | 0.25 | 0.12 | 0.14 | n.d. | 0.27 |
PF-01-08 | spindle | 69.34 | 21.27 | 2.33 | 5.90 | 0.17 | 0.77 | 0.15 | 0.07 | n.d. |
PF-01-14 | spindle | 82.98 | 5.71 | 4.00 | 6.60 | 0.51 | 0.20 | n.d. | n.d. | n.d. |
Unalloyed copper |
AA-02-43 | casket ornament | 99.52 | 0.08 | n.d. | 0.21 | 0.01 | 0.15 | n.d. | 0.03 | n.d. |
AA-03-59 | casket ornament | 96.45 | 1.90 | 0.26 | 0.65 | 0.07 | 0.16 | 0.15 | 0.06 | 0.30 |
AA-03-66 | casket ornament | 97.05 | 0.13 | 1.30 | 0.15 | 0.29 | 0.65 | 0.05 | 0.08 | 0.30 |
BC-03-117 | earring | 96.13 | 1.58 | 0.87 | 0.45 | 0.23 | 0.63 | n.d. | 0.11 | n.d. |
DV-01-04 | undetermined | 98.00 | 0.09 | 0.10 | 0.63 | 0.13 | 0.09 | 0.62 | 0.04 | 0.30 |
DV-01-05 | undetermined | 98.92 | 0.10 | n.d. | 0.03 | 0.25 | 0.13 | 0.57 | n.d. | n.d. |
DV-01-36 | undetermined | 98.55 | 0.09 | n.d. | 0.33 | 0.10 | 0.06 | 0.66 | 0.02 | 0.19 |
DV-02-53 | undetermined | 97.70 | 0.10 | 0.95 | 0.80 | 0.02 | 0.14 | 0.11 | 0.02 | 0.16 |
DV-02-54 | undetermined | 96.44 | 1.77 | 0.85 | 0.35 | 0.17 | 0.24 | n.d. | n.d. | 0.18 |
DV-02-79 | undetermined | 98.07 | 0.07 | 0.26 | 0.80 | 0.04 | 0.31 | 0.25 | 0.02 | 0.18 |
FIV-01-12 | buckle | 98.95 | 0.09 | n.d. | 0.64 | 0.05 | 0.04 | 0.09 | 0.01 | 0.13 |
PR-02-13 | nail | 98.55 | 0.25 | 0.07 | 0.66 | 0.23 | 0.20 | n.d. | 0.04 | n.d. |
Leaded unalloyed copper |
AR-01-42 | ring | 96.63 | 0.05 | 0.63 | 2.30 | 0.03 | 0.25 | 0.11 | n.d. | n.d. |
DV-01-19 | undetermined | 96.48 | 0.09 | 0.49 | 2.30 | 0.20 | 0.18 | 0.09 | 0.09 | 0.08 |
PR-02-06 | nail | 93.62 | 0.11 | 0.15 | 4.85 | 0.24 | 0.46 | 0.16 | 0.03 | 0.38 |
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unalloyed Cu: Cu + <2% Sn and <2% Zn;
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bronze: Cu + >2% Sn and <2% Zn;
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brass: Cu + >2% Zn and <2% Sn;
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ternary alloy (modern gunmetal): Cu + >2% Sn and >2% Zn;
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Leaded alloys: >2% Pb.
According to the adopted criteria, brass was the most frequent alloy in use at Mértola, being represented by 118 artefacts, 12 of which with more than 2 wt.% Pb. Seventeen objects were made of unalloyed Cu, three of which with more than 2 wt.% Pb. Ternary alloys are 36, 10 of which with more than 2 wt.% Pb. Finally, there are six bronzes, none of them with Pb higher than 2 wt.% (Fig. 4A). As for minor elements, i.e., Zn, Sn, and Pb when <2 wt.%, Fe, As, Ag, Ni, and Sb, their content tends to be quite variable, ranging from 0.21 to 3.25 wt.% in total.
At first glance, the results showed Zn to be the principal element to have been mixed with Cu and brass is the main alloy detected (Fig.4 B). At the same time, the data also indicate a seemingly random and unpredictable variability of the major components, i.e., Zn, Sn and Pb.
As the addition of each of these elements is known to alter the specific mechanical properties of a metal, a major archaeological question to address would be to find the reasons behind this variability. In this sense, the presence/absence of standardised compositional patterns can shed light not only on production technology aspects, but also on a range of issues related to different features of past societies. In fact, social strategies, technological choices, and economic constraints may have an impact on any single phase in the manufacturing process, including mining, smelting, melting, and casting processes, and any decisions made along the production chain, whether conscious or irrational, can directly affect the characteristics of the finished objects.
Based on this assumption, and looking at the overall Mértola data, it is quite clear that the high variability of the main elements found in the objects analysed does not allow clear compositional patterns to be identified. Tools, ornaments, and fragments that do not fall into any of the previous categories seem to be produced seamlessly together with alloys containing variable concentrations of Zn, Sn and Pb. Considering the high technological expertise in metal production reached during the Islamic Iberian Peninsula [12, 14, 17], it is not at all likely that the metalworkers who produced the objects found in Mértola were unaware of the mechanical properties of the different copper-based alloys to the point of not taking advantage of them. A detailed analysis of each of the alloys identified at Mértola will be presented with the aim of discussing the probable causes of this elemental variability.
Brass artefacts (Cu-Zn)
Brass is the predominant alloy produced and used at Mértola. It representsalmost69% of the entire assemblage analysed in this work, having been used to produce different types of metals, namely: 37 spindles, 31 earrings, 21 casket ornaments, 13 spatulas, 6 undetermined, 2 rings, and 1 sword sheath. Furthermore, only 12 out of 118 brasses contain more than 2% of Pb (Fig. 5 A).
Overall, Zn ranges from 2.1 to 22.3 wt.%, showing an average of c. 9.5 wt.%. Only one of the objects analysed (AA-02-29) has a Zn content higher than 22 wt.%, thus falling into the 22-28 wt.% Zn range, that is the typical interval for brasses produced with the method of cementation [18-20].
Fig. 5 B confirms the lack of correlation between Zn variability and the functionality of the artefacts. In fact, a Zn content in the range of 10-20 wt.% is known to be responsible for a golden yellow colour in the final alloy, making the latter particularly suitable for ornamental objects. When looking at Mértola's data, though, the 40 artefacts that fall in this range are evenly distributed between tools and ornaments, suggesting that the brightness and colour nature of an alloy was probably not considered relevant in producing finished objects with specific forms and functions.
With only few exceptions, almost all the brasses (105 out of 118) contain Zn between 4% and 20% (Fig. 5C), that is the range that Craddock considers as typical for objects produced through the mixing of pristine brass with 22 to 28 wt.% Zn with scrap copper-based alloys with lower Zn content [18].
The overall Zn content, however, is evidence for the use of scrap metals as raw materials to produce new objects. Further evidence in support of this hypothesis is the moderate and apparently random occurrence of Zn. When a brass is remelted, the alloy progressively loses about 10 wt.% of its Zn content, and a 4 to 5 wt.% additional Zn should be added to compensate the melting losses. Considering, for instance, the recycling of an ancient brass produced via the so-called cementation process and containing 28% Zn, Zn content may drop to about 25 wt.% after the first remelting, to 22 wt.% after a further remelting, and so on [21]. This means that the Zn variability observed in Mértola's brass objects is most likely the result of multiple remelting of scrap metal composed, in turn, of alloys with varying Zn content.
Another point to highlight is the presence of a small group of brass artefacts containing just over 20 wt.% Zn. These may be brasses that have undergone two or three remelting cycles or, alternatively, may have been produced by cementation throughout the so-called medieval method [22]. This involves the reaction of zinc vapour with liquid rather than solid copper, at higher temperatures and in open vessels. The use of this method at a temperature of about 1200 ºC makes it possible to produce a brass with about 20 wt.% Zn.
In any case, most brasses from the Almohad neighbourhood of Mārtulah contain a moderate Zn content and an overall low level of impurities. According to Gaudenzi Asinelli et al., this could be suggesting the use of sphalerite ((Zn,Fe)S) as a zinc ore [16]. In the case of the metals from Mértola, this is a relevant data as sphalerite zinc ores are common in the Iberian Pyrite Belt, a metallogenic province located in the SW Iberian Peninsula [23-25], thus suggesting the use of local minerals.
Unalloyed Cu artefacts
Pure coppers are relatively scarce, accounting for about 8.8% of the investigated collection. Of the 15 artefacts in this group, 12 contain less than 2 wt.% Pb. From a typological perspective, these Cu-artefacts include three casket ornaments, one ring, one earring, one buckle, seven undetermined objects, and two nails. The only two nails analysed in this paper are both made of copper, although with differences in terms of Pb content. Due to the small number of artefacts composed of unalloyed copper, the data does not allow however for any further noteworthy comment to be made.
Bronze artefacts (Cu-Sn)
Binary bronzes consist of only six objects (3.5% of the entire collection). Similar to the other alloys discussed so far, also bronze was not used to produce a specific type of object. Altogether, one earring, two undetermined objects, and two spindles were made of bronze, i.e., one ornament, two unknown, and two tools in terms of functionality.
The Sn content is highly variable, ranging from 2.93 to 9.09 wt.% (Fig. 6A). Minor elements like Zn, Pb, Fe, As, Ni, and Sb, range from 0.76 to 5.13 wt.% in total, and no leaded bronzes are present (Fig. 6B). Given their residual occurrence, none of impurities had any significant impact on the mechanical properties of the alloys.
As it is well known, the addition of Sn to Cu lowers the melting temperature of Cu, and improves the mechanical properties of the metal, making the alloy physically more resistant to impacts. In this respect, the mechanical effects that the presence of Sn may have on the finished alloy begin to become evident only at Sn concentrations above 3-4% [26], with the best outcome with Sn % above 10-15 wt.%.
Considering the Sn content found in the bronzes from the Almohad neighbourhood of Mértola, it is quite evident that the addition of fresh Sn during the melting process was not a technological option for the metalworkers that produced these metals. As such, the reduced content of Sn is a further indication that, at that time, the use of recycled scraps as a raw material, instead of alloying Cu and Sn in suitable proportions, was a well-established practice. The reduced amount of Sn in the finished objects is a consequence of the decrease in concentration that this element experiences as a consequence of the recycling process. Each time a tin-bronze is remelted, Sn gradually decreases through volatilization, leading to the production of objects with less Sn content than those used as scrap. The higher the number of remelting episodes, therefore, the lower the amount of tin in the final alloy [18].
When placed in its historical context, the low concentration of tin in the alloys found in Mértola cannot be considered unexpected [27]. In fact, no tin mines have so far been identified in the South of Portugal with the most likely source of tin at the beginning of the 2nd millennium being located in the Iberian Peninsula northwest, where tin had been exploited since antiquity [28]. However, it is very likely that with the Reconquista underway, these tin mines were no longer accessible to Moors as in the first quarter of the 2nd millennium Iberia northwest was already under the firm control of the Christian kingdoms.
The low concentration of tin in the alloys analysed in this paper could therefore be explained by a shortage of Sn supply due to the interruption of the tin trade to southern Portugal. However, it cannot be underestimated that tin, during the Islamic period, was also used for other craft productions, in particular for pottery glazes [29-35]. Thus, it is also possible that the little available tin, given its scarcity, may have been deliberately restricted to productions of greater social and artistic values such as prestige pottery, rather than for metal objects of daily use.
Ternary alloys artefacts (Zn-Sn-Pb)
Ternary alloys represent 18.7% of the entire assemblage, and includes ten spindles, seven casket ornaments, six earrings, three oil lamp sticks, two rings, two spatulas, and two undetermined objects.
All the ternary alloys show very reduced tin concentration, and a variability in composition of both Zn (from 2 to 13 wt.%), and Pb (26 of the 36 ternary objects have less than 2 wt.% Pb, ranging from 0.3 to 11 wt.%) (Fig. 7). A clear pattern linking the variability of major elements and the typology of the artefacts is, once again, not detectable as evidenced by Fig. 8.
The composition of ternary alloys appears to be a further argument in favour of a predominantly scrap-based metallurgy in which fresh ores were not added to the melt. Low levels of Zn and Sn, in particular, confirm the hypothesis already discussed above which regards the use of scrap as raw material to produce new objects as a very common practice of the time.
Impurities
As for impurities, i.e., elements whose concentration is less than 2 wt.%, they most likely derive from minor metallic elements present in the ore and reduced unintentionally during the smelting process that end up incorporated into the finished objects. Their concentration depends on different factors such as the quantity of impurities in the ore or the smelting technology in use. Attempting to address questions concerning to origin of raw materials through the identification of impurity patterns is a controversial issue in archaeology, although it is quite clear that some chemical characteristics of the ore are still detectable in the finished objects. The point here is that the composition of an ore source is not homogeneous, and impurities can vary even at different locations within the same ore (Fig. 9).