Pin without head and light-brown patina - Tin Bronze - Late Bronze Age - Switzerland

Marianne. Senn (EMPA, Dübendorf, Zurich, Switzerland) & Christian. Degrigny (HE-Arc CR, Neuchâtel, Neuchâtel, Switzerland)

Complementary information

Nothing to report.

Stratigraphic representation: none.

Fig. 4: Stratigraphic representation of the object in cross-section using the MiCorr application. This representation can be compared to Fig. 10.

Complementary information

Nothing to report.

Analyses performed:
Metallography (etched with ferric chloride reagent), Vickers hardness testing, XRF, ICP-OES, SEM/EDS, XRD, Raman spectroscopy.

The remaining metal is a tin bronze and contains copper sulphide as well as heavy metal (Pb-rich) inclusions (Table 1, Figs. 5 and 6). Close to the surface of the remaining metal, copper sulphide inclusions are elongated and form rows (Fig. 5). The etched structure of the tin bronze shows polygonal grains; some of them are twinned (Fig. 7). In the centre of the sample and on the edges, the grains are smaller. The copper sulphide inclusions are located at the grain boundaries and in the grains. The average hardness of the metal is about HV1 110.


Elements Cu Sn Pb Sb As Ag Fe Ni Co Zn
mass% 89.22 9.57 0.34 0.26 0.19 0.15 0.09 0.05 0.06 0.05

Table 1: Chemical composition of the metal. Method of analysis: ICP-OES, Laboratory of Analytical Chemistry, Empa.

Complementary information

Nothing to report.

The corrosion crust is regular in thickness (100µm). One third is missing (Fig. 3). At the metal - corrosion crust interface, there is a crack showing that the latter has separated from the metal core along its whole length (Figs. 8 and 9). The corrosion crust can be divided into three distinct layers (CP1-3). Directly above the crack is a first dense but cracked and irregular inner layer (CP3, Figs. 8 and 9). In bright field it appears brown (Fig. 10), in polarised light dark brown (Fig. 11). It is separated from the adjacent layer by a clear line (Figs. 9 and 10). The second layer (CP2) is dense with little porosity (Figs. 8 and 9). In bright field it appears light brown (fig. 10), in polarised dark grey (Fig. 11). The third and outermost layer (CP1) appears light brown in bright field (Fig. 10), contains particles (Fig. 9) and is very porous (visible as golden reflections under polarized light, Fig. 11). The elemental chemical distribution of the SEM image selected reveals that the inner layer (CP3) is depleted in Cu, but rich in Sn,O and Si (Fig. 12 and Table 2) and its interface with the intermediate layer (CP2) could represent the limit of the original surface (Figs. 8 and 12). The second and third layer (CP2 and CP1) are Fe,Cu and S-rich (Fig. 12) and have a composition similar to chalcopyrite/CuFeS2 (Table 2). This was confirmed by XRD. The particles (inclusions) have a composition similar to covelline or covellite/CuS (Table 2). Both chalcopyrite and covelline have been identified by Raman spectroscopy (Figs. 13 and 14).



S Fe Cu O Si Sn Total
CP1 and CP2 35 30 34 < < < 99
Particles in CP1 26 4.1 68 < < < 98
CP3 5.8 5.0 13 32 2 41 99

Table 2: Chemical composition (mass %) of the corrosion layer from Fig. 10. Method of analysis: SEM/EDS, Laboratory of Analytical Chemistry, Empa.

Complementary information

Nothing to report.

Corrected stratigraphic representation: none.

The pin is made from tin bronze and has been annealed after cold working. It is covered with a regular, light-brown patina typical of lake context (Schweizer 1994). The inner, thin Sn-rich corrosion layer contains soil elements such as Si. The light-brown, thick intermediate and outer corrosion layers have the composition of chalcopyrite. This object was certainly abandoned rather quickly in an anaerobic, humid and S and Fe-rich environment, favouring the formation of the above mentioned compound. The limit of the original surface can be located between the chalcopyrite and the Cu depleted but Sn-rich inner corrosion layer. Thus, the corrosion is a type 1 according to Robbiola et al. 1998.

References on object and sample

References object

1. Rychner-Faraggi A-M. (1993) Hauterive – Champréveyres 9. Métal et parure au Bronze final. Archéologie neuchâteloise, 17 (Neuchâtel).
2. Hochuli, S. et al. (1988) SPM III Bronzezeit , Verlag Schweizerische Gesellschaft für Ur- und Frühgschichte Basel, 76-77, 379.


References sample

3. Empa Report 137 695/1991, P.O. Boll.
4. Rapport d'examen, Lab. Musées d'Art et d'Histoire, Geneva GE, 87-194 à 87-197.
5. Schweizer, F. (1994) Objets en bronze provenant de sites lacustre: de leur patine à leur biographie. In: L'œuvre d'art sous le regard des sciences (éd. Rinuy, A. and Schweizer, F.), 143-157.

References on analytic methods and interpretation

6. Robbiola, L., Blengino, J-M., Fiaud, C. (1998) Morphology and mechanisms of formation of natural patinas on archaeological Cu-Sn alloys, Corrosion Science, 40, 12, 2083-2111.