Sickle Auv 310 - Late Bronze Age - Switzerland

Sickle Auv 310

Rémy. Léopold (HE-Arc CR, Neuchâtel, Neuchâtel, Switzerland)

Complementary information

None.

The schematic representation below gives an overview of the corrosion structure encountered on the sickle from a first visual macroscopic observation.

Strata Type of stratum Principal characteristics
CP1 Corrosion product Brown, pearly, thin, discontinuous, compact, brittle, very soft
CP2 Corrosion product Black, matte, thin, discontinuous, compact, powdery, very soft
CP3 Corrosion product Extra light grey, matte, thin, compact, powdery, soft
M1 Metal Yellow, thick, continuous, compact, tough, very hard

Table 1: Description of the principal characteristics of the strata as observed under binocular and described according to Bertholon's method.

Fig. 8: Stratigraphic representation of the corrosion structure of the sickle observed macroscopically under binocular microscope using the MiCorr application with reference to Fig. 7. The characteristics of the strata, such as discontinuity, are accessible by clicking on the drawing that redirects you to the search tool by stratigraphy representation, credit: MiCorr_HE-Arc CR, L.Rémy.

Complementary information

None.

Analyses performed:

Non-invasive approach

XRF with handled portable X-ray fluorescence spectrometer (NITON XL5), General Metal mode, acquisition time 60s (filters: Li20/Lo20/M20).

XRF analyses of the sickle were carried out on eight representative areas (Fig. 5). Points 1 and 2 were done on the brown corrosion layer of each side (CP1), points 3 and 4 on the yellow areas covered with black and grey corrosion products (CP2 and CP3) of each side, and points 5 and 6 on the black corrosion layer of each side (CP2), and points 7 and 8 on the grey corrosion layer of each side (CP3). All strata (soil, corrosion products, and metal) are analyzed at the same time.

The metal is presumably a tin bronze alloy with traces of Sb, As, Pb. The other elements detected are : Fe, S, Si, Zn, Al and Ag.

Results of points 1 and 2 are very similar, CP1 is rich in Fe and S, but delepled in Cu and Sn.

The results of points 3 and 4 are similarly very close, but different from those of points 1 and 2: we are closer to the residual metal but it is still covered with corrosion products containing Fe and S.

Results of point 5 indicate that again we are close to the metal surface with even less Fe and S.

Results of points 6 and 7 are very similar and are closer to the results of points 1 and 2.

Results of point 8 are closer to those of points 1 and 2 but with less S.

Elements (mass %) Cu Fe S Sn
Si Zn Pb Al Sb As Ag  
  % +/-2σ % +/-2σ % +/-2σ % +/-2σ % +/-2σ % +/-2σ % +/-2σ % +/-2σ % +/-2σ % +/-2σ % +/-2σ TOTAL
1 44.0 0.08 23.2 0.06 24.5 0.06 5.2 0.02 0.6 0.02 0.2 0.02 1.3 0.02 0.3 0.08 0.5 0.01 <LD <LD 0.1 0.01 99.9
2 44.5 0.07 21.2 0.06 25.9 0.05 5.0 0.02 0.7 0.02 0.1 0.01 1.3 0.02 0.5 0.07 0.5 0.01 <LD <LD 0.1 0.01 99.8
3 63.1 0.16 11.7 0.06 16.0 0.08 6.1 0.04 0.8 0.06 0.1 0.02 1.4 0.02 <LD <LD 0.6 0.01 <LD <LD 0.1 0.01 99.9
4 62.4 0.12 11.7 0.06 16.4 0.07 5.9 0.03 0.9 0.05 <LD <LD 1.3 0.02 0.4 0.12 0.5 0.01 <LD <LD 0.1 0.01 99.6
5 66.4 0.15 1.9 0.03 13.9 0.08 9.2 0.05 1.5 0.07 0.1 0.02 4.1 0.04 0.4 0.14 0.8 0.02 0.9 0.02 0.2 0.01 99.4
6 37.5 0.12 27.4 0.09 21.5 0.08 4.8 0.03 4.9 0.09 0.1 0.02 1.0 0.02 1.8 0.15 0.4 0.01 <LD <LD 0.1 0.01 99.5
7
37.9 0.08 28.5 0.07 23.0 0.05 4.9 0.05 2.4 0.04 1.2 0.09 0.5 0.02 0.6 0.02 0.8 0.01 <LD <LD <LD <LD 99.8
8
42.7 0.17 26.5 0.12 14.7 0.1 7.2 0.05 4.0 0.12 1.6 0.2 0.6 0.02 1.2 0.03 0.9 0.03 <LD <LD 0.1 0.01 99.5

Table 2: Chemical composition of the surface of the pin at eight representative points shown in Fig. 5, Method of analysis: XRF.

None.

Complementary information

Rychner (1987) indicates that the metal of the object is a bronze. 

The appearance of CP1 and its composition (Cu, Fe, S) seem to indicate that it is either itaite or chalcopyrite.

Complementary information

According to Rychner (1987), the surface of the object is covered with chalcopyrite (CuFeS2).

The corrosion structure has only been documented in binocular mode (Fig. 8).

The sickle is made from a tin bronze. The XRF analysis shows that the brown corrosion layer (CP1) have higher %Fe and %S and lower % Cu while CP2 is richer in %S than Fe. It would indicate that CP1 is made of copper iron sulfide like chalcopyrite (CuFeS2) as described by Rychner (1987). According to Schweizer's paper from 1994, it would mean that CP1 could be a lake patina which was generated on the metal by the presence of sulfate-reducing bacteria in the burial environment.

References on object and sample

Object files in MiCorr

1.    MiCorr_Sickle Auv-322
2.    MiCorr_Sickle Auv-313

References object

3. Rychner, V. (1987) Auvernier 1968-1975: le mobilier métallique du Bronze final Formes et techniques. In: Cahiers d´archéologie romande 37, Auvernier 6. 39-40.
4. Rapport d'examen, Lab. Musées d'Art et d'Histoire, Geneva GE, 87-194 à 87-197.
5. Schweizer, F. (1994) Bronze objects from Lake sites: from patina to bibliography. In: Ancient and historic metals, conservation and scientific research (eds. Scott, D.A., Podany, J. and Considine B.B.), The Getty Conservation Institute, 143-157.