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Identification and Creation

Object Number
1987.135.40
Title
Serpentine Fibula
Other Titles
Former Title: Long Catch Plate Fibula
Classification
Jewelry
Work Type
pin, fibula
Date
mid 8th century BCE
Places
Creation Place: Ancient & Byzantine World, Europe
Period
Iron Age
Culture
Italic
Persistent Link
https://hvrd.art/o/304077

Physical Descriptions

Medium
Bronze
Technique
Hammered
Dimensions
10.5 x 4.1 x 0.2 cm (4 1/8 x 1 5/8 x 1/16 in.)
Technical Details

Chemical Composition: EMP analysis from sample, Bronze:
Cu, 94.63; Sn, 3.79; Pb, 0.28; Zn, 0.00; Fe, 0.23; Ni, 0.14; Ag, 0.10; Sb, 0.39; As, 0.16


J. Wolfe, June 1998

Technical Observations: The serpentine fibulae were fabricated using a combination of wire-making techniques. Most of the wires were cast into rods and cold worked with a hammer to lengthen them. The wire was hammered to shape two springs and a catchplate. The shape of the wire among the fibulae was formed either round, square, or hexagonal in cross-section. The variation in the shape of a single length of wire resulted from the metal being hammered to create different elements. This can be seen in a spring detail of 1987.135.35, where a square-shaped wire becomes round at the springs. Also visible on 1987.135.35 are square hammer marks adjacent to the spring that give more evidence of hand shaping. The diameter of the serpentine wires has an even taper that gradually becomes thinner towards the tip of the pin.

Three of the serpentine fibulae were tested for alloy composition using EMP analysis (1). The results for all three fibulae (1987.135.40, 1987.135.48.A-B, and 1987.135.50.A-B) revealed a composition of low-tin bronze, with the tin concentration ranging from 4 to 9% (2). All of the samples contained traces of antimony and arsenic, which is a common combination found in tetrahedrite-type copper ores. Two different beam sizes were used for monitoring inclusions in the metal. All of the samples, when monitored with the larger beam raster, showed a consistent increase in the lead and sulfur content, which is a result of copper sulfide or lead globule inclusions.

All nineteen serpentine fibulae were x-radiographed, and the exposures showed a dark line running along the center axis of the wire on at least ten of them. The line can be seen in a detail of the x-radiograph of 1987.135.47. The center of the wire is the thickest section and should be the most radio-opaque (white in the x-radiograph); therefore the dark line could indicate one of three possible situations: that the fibula has a hollow center, that there is a small groove along the outside surface of the wire, or that a shrinkage occurred during casting, which is called coring. There is a visible groove in the wire adjacent to the catchplate of 1987.135.37. However, other fibulae showing a line in the x-radiograph do not have visible grooves in the surface of the wire. This raises the question of whether the wire could have also been fabricated using a strip-folding technique. This technique was common for gold wire making in antiquity; it involves folding a flat ribbon of metal into a C-shape and joining the sides to create a wire that has a seam down one side (3).

In order to gain more information about the wire and its fabrication method, a transverse and a longitudinal section of wire were sampled from the pin break of 1987.135.48.A-B. These samples were polished for metallographic analysis (4). The transverse section of wire showed a fissure across the center of the wire. Under polarized light, the fissure is black in coloration, and SEM-EDX analysis showed that it contains copper and tin. Large pits of corrosion have disrupted the circumference of the wire, making the morphology of the fissure difficult to read. It is not possible to determine from this sample if the fissure extends out to one edge, which would indicate a strip-folding technique of manufacture (5). The fissure in this case is most likely coring, which could also be an explanation for a dark line seen in the x-radiographs.

The longitudinally mounted cross-section section of 1987.135.48.A-B shows elongated inclusions that run parallel to the axis of the wire. The drawn-out inclusions resulted from cold working the metal to lengthen the wire. The inclusions turn black under crossed polars, and analysis using SEM-EDX indicates that they are sulfide inclusions, since they contain only sulfur and copper (no tin).

NOTES:

1. EMP analyses were carried out by David Lange at Harvard University using a Cameca MBX Electron Microprobe. A wavelength dispersive spectrometer (WDS) and a Sandia ZAF85 for matrix correction were used. The analyses were done at 15 KeV with a 45 nanoamperes beam current. The small beam (32 x 32 µm raster) included the inclusions. The sample from 1987.135.50.A-B was not large enough to be analyzed with the large beam. Standards were used for pure elements, with three exceptions where pyrite (FeS2) was used for S; GaAs for As; and galena (PbS) for Pb. X-radiograph lines used were: K-alpha S, Fe, Co, Ni, Cu, Zn; L-alpha As, Ag, Sn, Sb; M-alpha Pb. The analytical precision for the EMP data is less than 1% for values above 4%, 1-2% for values from 0.4 to 4%, and 2-10% for values from 0.1 to 0.4%.

2. Other alloy references of Iron Age fibulae include a brooch from Tarquinia having Sn, 12.5%; Pb, 0.3%; Cu, 86.6%; see U. Anemüller, E. Formigli, and W. R. Teegen, “Technologische und experimentelle Studien und einem früheisenzeitlichen Fibelfragment aus Tarquinia,” Gedenkschrift für Jürgen Driehaus (Mainz, 1990) 31-47, esp. 40. For Italian and Sardinian bronzes that are tin-bronze and have similar alloys and impurities as the Harvard fibulae (Sn, 4.2%-10%; As, 0.005-0.4%; Sb, 0.03-0.35%; Co, 0.003-0.05%; Ag, 0.4-0.6%; Fe, 0.04-0.4%; Ni, 0.1-0.3%), see P. Craddock, “The Metallurgy of Italic and Sardinian Bronzes,” in Italian Iron Age Artefacts in the British Museum, ed. J. Swaddling (London, 1986) 143-52. For Sicilian bronzes with sulfur and iron inclusions, indicating sulfide ores, see C. Giardino, Il Mediterraneo Occidentale fra XIV ed VIII secolo a.C.: Cerchie minerarie e metallurgiche = The West Mediterranean between the 14th and 8th centuries B.C.: Mining and Metallurgical Spheres, BAR Int. Ser. 612 (Oxford, 1995) 320.

3. For gold wire making techniques, see A. Oddy, “The Production of Gold Wire in Antiquity: Hand-Making Methods Before the Introduction of the Draw-Plate,” Gold Bulletin 10.3 (1977): 79-87; and id., “Does Strip-Drawn Wire Exist from Antiquity?” MASCA Journal 4.4 (1987): 175-77. For a study of strip-drawn wire from Narce that has a groove running parallel to the axis of the wire, see G. Warden, “Strip Drawn Wire from Iron Age Narce,” Studi Etruschi 46 (1978): 265-67. See also E. Formigli, “Modi di fabbricazione di filo metallico nell’oreficeria etrusca,” Studi Etruschi 47 (1979) 281-92, who makes the point that a variety of techniques could have been used in wire making. Formigli also claims that it is possible wire drawing could have been done during the Iron Age using draw