*5.1. Lupa Capitolina: TL Study of the Clay Core*

During the extensive restorations underwent in the period from 1997 to 2000, several samples of clay core were taken from the *Lupa Capitolina* and submitted to TL studies with the aim of dating its casting [4]. This goal could not be directly reached, due to the complex environmental irradiation history. Nevertheless, it was possible to demonstrate that the statue was cast with maximum of probability between the VIII and XIV century AD, so the traditionally reported Etruscan origin of the statue was ruled out. Recently, Calcagnile et al. [7] had the opportunity to apply AMS radiocarbon dating on, overall, 34 organic residues sampled form the casting cores within the statue.

In view of these results, we crosschecked the TL dates with the radiocarbon ones. We considered the combination of the thirty-four 14C ages (see Figure 6 in reference [7]).

For what concerns the TL dating, it was possible to have access to the interior of the statue for clay core sampling, by hand, by dry laser ablation and with an endoscope specially adapted [4]. The cores had a homogeneous calcareous marl-like composition, rich in silicate and carbonate components, to which abundant inorganic temper was added [8]. For the experimental details, see Martini and Sibilia [4].

By summarising the achieved results, the TL emission of the samples was characterised by a good sensitivity to radiation, but sometimes by scarce reproducibility; therefore, errors in palaeodose were quite high (±10%). As for the dose rate evaluation, even if the concentrations of uranium and thorium were quite homogeneous and the potassium oxide contents were more scattered (standard deviation, 26% of the mean value). The possibility of enrichment of potassium due to percolation of water could perhaps account for this phenomenon.

Finally, speculations on the mean water content during time were performed; the saturation water of the samples was evaluated, but this measured value was used with great caution, giving account for possible significant variations. Moreover, as we already mentioned in the previous section, the assessment of the ambient contribution to the annual dose rate is problematic and this case study was no exception; the measured value refers only to the conservation in the museum and does not take into account any correction for the attenuation due to the metal layer.

So, as expected, TL dating results were strongly dependent on the attenuation of the external dose by the bronze thickness and on the water content. In such a situation, it was therefore attempted a probabilistic approach to the dating problem by focusing the attention on the five solid samples taken from the inner part of the Lupa (D1343/LL4, D1278/LS, D1342/M1, D1344/M2 and D1226/V1, see Figure 2). For these samples, dust contamination could be excluded and humidity conditions and external irradiation were reasonably more constant during time.

**Figure 2.** *Lupa Capitolina*, sampling position of the clay core samples.

In Figure 3, the dating results are plotted as a function of the water content, excluding the extreme values relative to dry and saturated conditions, which were very unlikely. The results shown suggest that the casting could not have occurred before the VIII century nor after the XIV century.

**Figure 3.** Possible dates for casting (water content, 25–75% of saturation; effective external dose rate, 1.5 ± 0.5 mGy/a).

Putting all the 14C and TL data together (see Figure 4), it appears that, regardless of the chosen percentage of saturation of water content, the TL date of three out of the five samples agree within two standard deviations with the radiocarbon date (namely D1343/LL4, D1344/M2 and D1226/V1).

The two samples (D1278/LS and D1342/M1) in disagreement with the combined radiocarbon date are little dependent on the water content. These results seem to put in evidence that if the clay cores are sampled from volumes that have reasonably uniform humidity conditions and external irradiation over time, the estimation of the water content inside the bronze little affects the obtained age.

At this point, we could choose 50% as a value for water content and we applied the R\_Combine function of OxCal 4.4.4 [9] to the two sub-set of samples (D1343/LL4, D1344/M2, D1226/V1 and D1278/LS, D1342/M1). The results obtained from the first sub-set (see Figure 5) show an agreement with a confidence level of 95.4% with the radiocarbon age.
