ADVANCED MATERIALS & PROCESSES | OCTOBER 2023 19 TABLE 1 — µ-XRF ANALYSIS OF SILVER BULL FEATURES (WT%) Feature Code Fe σ Ni σ Cu σ Zn σ As σ Ag σ Horn B1 0.16 0.05 0.05 0.00 0.15 0.11 0.02 0.00 0.26 0.13 98.10 0.40 Head B2 0.46 0.44 0.05 0.01 2.93 2.65 0.03 0.01 0.20 0.09 95.01 2.96 Ear B3 0.09 0.04 0.03 0.01 3.13 1.00 0.01 0.01 0.21 0.08 95.74 1.09 Bowl B4 0.11 0.07 0.04 0.00 3.48 0.52 0.02 0.01 0.12 0.04 94.88 0.62 Shoulder B5 0.09 0.06 0.04 0.00 5.08 0.82 0.03 0.01 0.20 0.09 93.67 0.97 Cloth B6 0.04 0.02 0.03 0.00 0.36 0.45 0.00 0.00 0.01 0.01 98.84 0.46 Base B7 0.18 0.12 0.02 0.01 0.36 0.63 0.00 0.00 0.09 0.08 98.94 0.78 Hoof B8 0.05 0.01 0.03 0.00 0.01 0.02 0.00 0.00 0.00 0.01 99.52 0.14 SE (95% CI) 0.01 0.01 0.79 0.07 0.01 0.70 Feature Code Sn σ Sb σ Au σ Pb σ Bi σ Horn B1 0.32 0.13 0.05 0.02 0.06 0.00 0.77 0.12 0.05 0.01 Head B2 0.25 0.07 0.04 0.02 0.06 0.01 0.63 0.16 0.05 0.02 Ear B3 0.23 0.01 0.02 0.01 0.05 0.00 0.47 0.17 0.04 0.02 Bowl B4 0.33 0.08 0.04 0.02 0.05 0.00 0.75 0.07 0.04 0.01 Shoulder B5 0.31 0.12 0.04 0.02 0.06 0.01 0.40 0.14 0.05 0.01 Cloth B6 0.22 0.00 0.03 0.01 0.05 0.00 0.37 0.05 0.02 0.00 Base B7 0.22 0.00 0.03 0.01 0.05 0.00 0.17 0.08 0.01 0.01 Hoof B8 0.22 0.00 0.02 0.01 0.05 0.00 0.21 0.03 0.03 0.00 SE (95% CI) 0.03 0.01 0.02 0.17 0.01 using a fundamental parameter-based quantification method provided by Bruker. The accuracy of the method was verified against certified reference materials of known composition. For this purpose, three silver reference materials, namely 133X AGA1, 133X AGA2, and 133X AGA3 produced by MBH Analytical Ltd. UK, were used for calibrating the XRF analysis of silver. Eight areas of the bull were analyzed including the horn, head, ear, spouted bowl, shoulder, patterned cloth, bottom, and a hind hoof. At least five points were analyzed from each area and an average is presented as the final result. All areas inspected and analyzed are marked in Fig. 1. µ-XRF RESULTS The results of µ-XRF quantification of eight different areas are presented in Table 1. The analysis shows that silver is the main constituent in the composition of all pieces. In addition, 3-5 wt% copper has been detected as a significant alloying element in four of the pieces (head, ear, bowl, and shoulder) indicating they are made using a debased silver alloy. Gold, iron, nickel, zinc, arsenic, lead, and bismuth are detected as trace elements. Table 2 shows results of NAA analysis presented by Hansen et al.[1] According to the NAA results, unalloyed but impure silver and debased silver Fig. 1 – Kneeling Bull Holding a Spouted Vessel (The Metropolitan Museum of Art, 66.173, Purchase, Joseph Pulitzer Bequest, 1966) with areas of µ-XRF analyses indicated[8]. method widely used during the past few decades to analyze and characterize the chemical composition of different types of archaeological and artistic materials. This method offers many benefits to museums and cultural institutions: It is noninvasive, useful for a wide range of materials, sensitive enough to measure major, minor, and trace elements, and is fast and easy to use[2]. This technique has been used for characterization of the chemical composition of different types of inorganic materials such as metals, pigments, ceramics, glasses, and glazes. Due to numerous modifications over the years, it is now becoming one of the most precise and portable methods for instrumental analysis available[3-7]. To identify the composition of the alloys used to make different pieces of the silver bull, µ-XRF was employed directly on the surface using an open architecture Bruker Artax 400 spectrometer with unfiltered Rh radiation at 50 kV, 700 µA, and a 1-mm collimator for 120 sec live-time acquisition. Elemental composition of the alloy was calculated
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