Tang fragment of a knife HR-6567
Marianne. Senn (Empa, Dübendorf, Zurich, Switzerland) & Christian. Degrigny (HE-Arc CR, Neuchâtel, Neuchâtel, Switzerland) & Naima. Gutknecht (HE-Arc CR, Neuchâtel, Neuchâtel, Switzerland) & Rémy. Léopold (HE-Arc CR, Neuchâtel, Neuchâtel, Switzerland)
Credit HE-Arc CR, N.Gutknecht/L.Rémy.
Fragment de Tang avec des produits de corrosion brun-jaune brillants encore en place localement (Fig. 2). Dimensions : L = 2,9 cm ; Ømax. = 6,8 mm ; WT = 4,9 g.
Household implement
Hauterive - Champréveyres, Neuchâtel, Neuchâtel, Switzerland
Excavation in 1983-1985, layer 3
Late Bronze Age
Hallstatt B1 (1054/1037BC _ 1000BC)
Lake
Laténium, Neuchâtel, Neuchâtel
Laténium, Neuchâtel, Neuchâtel
HR 6567
No conservation data available, but a coating and inventory number is visible on the surface.
L'objet a été échantillonné en 1987 pour analyse. La documentation des strates en mode binoculaire sur le fragment restant de l'objet a été réalisée en 2022.
Credit HE-Arc CR, N.Gutknecht/L.Rémy.
La représentation schématique ci-dessous donne un aperçu de la structure de corrosion rencontrée sur le fragment à partir d'une première observation macroscopique visuelle.
| Couches | Type de strate | Principales caractéristiques |
| NMM1 | Matériau non métallique | Film/revêtement, transparent, mince, continu |
| CP1 | Produit corrosif | Brun, nacré, fin, discontinu, compact |
| CP2 | Produit corrosif | Jaune foncé, épais, discontinu, compact, dur |
| CP3 |
Produit corrosif | Layer, dark grey, thin, scattered, non-compact, soft |
| M1 | Metal | Olive, thick, metallic, soft |
Table 1: Description of the principal characteristics of the strata as observed under binocular and described according to Bertholon's method.
The NMM1 seems to be a polymer coating added after excavation of the object.
This cross-section shows a lateral cut through the tang (Fig. 3). Most of the corrosion structure is absent (Fig. 7).
Leaded Bronze
Cold worked with partial annealing
MAH 87-196
Musées d'art et d'histoire, Genève, Geneva
Musées d'art et d'histoire, Genève, Geneva
1987, metallography and corrosion characterisation
None.
Analyses performed:
Non-invasive approach
XRF with handheld portable X-ray fluorescence spectrometer (NITON XL5). General Metal mode, acquisition time 60s (filters: Li20/Lo20/M20).
Invasive approach (on the sample)
Metallography (etched with ferric chloride reagent), Vickers hardness testing, ICP-OES, SEM/EDS (conditions provided in the About tab of the MiCorr application), XRD.
XRF analyses of the tang fragment of a knife were carried out on two representative areas (Fig. 3). Point 1 was done on the dark yellow corrosion layer (CP2), while point 2 was performed on the remaining metal surface. For both points, soil, corrosion products and metal are analyzed at the same time.
The metal is presumably a tin bronze alloy. The other elements detected are: Fe, S, Pb, Si, Al, Sb, As, Co, Ag, Zn.
Results of point 1 are very different from those of point 2, they indicate the enrichment in Fe and in S and depletion in Cu.
|
Elements (mass %) |
Cu |
Fe |
S |
Sn |
Pb |
Si |
Al |
Sb |
As |
Co |
Ag |
Zn |
|
||||||||||||
|
|
% |
+\-2σ |
% |
+\-2σ |
% |
+\-2σ |
% |
+\-2σ |
% |
+\-2σ |
% |
+\-2σ |
% |
+\-2σ |
% |
+\-2σ |
% |
+\-2σ |
% |
+\-2σ |
% |
+\-2σ |
% |
+\-2σ |
Total |
|
1 |
37.0 |
0.1 |
32.0 |
0.09 |
23.5 |
0.08 |
4.0 |
0.02 |
<0.1 |
0.01 |
1.5 |
0.06 |
0.5 |
0.1 |
0.4 |
0.01 |
0.2 |
0.01 |
0.2 |
0.04 |
0.1 |
0.01 |
<0.1 |
0.02 |
99.4 |
|
2 |
77.0 |
0.1 |
1.0 |
0.02 |
3.5 |
0.03 |
9.0 |
0.04 |
2.0 |
0.03 |
2.0 |
0.05 |
0.5 |
0.1 |
0.7 |
0.02 |
2.0 |
0.04 |
0.2 |
0.01 |
0.3 |
0.01 |
<0.1 |
0.02 |
99.5 |
Table 2: Chemical composition of the surface of the tang at two representative areas shown in Fig. 3. Method of analysis: XRF, UR-Arc CR.
The remaining metal is a leaded bronze (Table 2) containing numerous copper sulphide and tiny Pb inclusions (Figs. 8-10, 12 and Table 4). The porosity within the metal is high, particularly along a band through the middle of the sample (Figs. 7 and 8). The etched structure of the leaded bronze shows small, regular polygonal grains, some with twinning (Fig. 9). Slip lines appear in grains close to the metal surface (Fig. 9). The average hardness of the metal is HV1 120.
| Elements | Cu | Sn | Pb | Ni | Sb | As | Co | Ag | Fe | Zn |
|---|---|---|---|---|---|---|---|---|---|---|
| mass% | 87.52 | 8.02 | 1.46 | 1.04 | 0.81 | 0.60 | 0.24 | 0.21 | 0.05 | 0.03 |
Table 3: Chemical composition of the metal. Method of analysis: ICP-OES, Laboratory of Analytical Chemistry, Empa.
| Elements | O | S | Fe | Cu | Total |
|---|---|---|---|---|---|
| mass% | 1.5 | 20 | 1.0 | 71 | 93 |
Table 4: Chemical composition of dark-grey inclusions. Method of analysis: SEM/EDS, Laboratory of Analytical Chemistry, Empa.
Credit HE-Arc CR.
Credit HE-Arc CR.
Polygonal and twinned grains + strain lines (metal surface) with pores
Cu
Co, Ni, As, Ag, Sn, Sb, Pb
None.
The metal has lost most of its original corrosion layer, the remainder having an average thickness between 60 and 190µm (Fig. 6). In some areas up to three corrosion strata are visible (Fig. 11). In polarised light (Fig. 12), the corrosion stratigraphy appears more clearly: it is composed of a dense black inner layer, an intermediate thick brown layer with bright spots (indicating porosity) and an outer red layer with white particles. The elemental chemical distribution of the SEM image reveals that the black inner layer (CP3) is Sn-rich, but contains Cu, O, Fe, Si, P, Pb, Ni, As, Ca and S (Table 5, Figs. 12-13). The brown layer (CP2) contains S, Fe and Cu and has a composition similar to chalcopyrite/CuFeS2 (Table 5, Figs. 12-13). This was confirmed by past XRD analyses carried out by Schweizer (1994, museum report (1987)). The red layer (CP1) is an iron oxide (main elements Fe and O) and is contaminated with calcite/CaCO3 particles (S1) (Table 5, Figs. 12-13).
|
Elements |
O | Fe | Ni | Cu | Si | P | S | Ca | As | Sn | Pb | Total |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| CP1, red layer | 37 | 51 | 1.8 | < | < | < | < | 2 | 1 | < | < | 93 |
| CP2, brown layer | < | 30 | < | 42 | < | < | 35 | < | < | < | < | 107 |
| CP2, white particles | 50 | < | < | <1 | < | < | < | 39 | < | < | < | 90 |
| CP3, black layer | 39 | 5 | 1 | 5 | 4 | 4 | < | < | <1 | 37 | 4 | 100 |
Table 5: Chemical composition (mass %, <: below the detection limit) of the corrosion layers (from Figs. 12). Method of analysis: SEM/EDS, Laboratory of Analytical Chemistry, Empa.
Credit HE-Arc CR.
Fig. 11: Micrograph of the metal sample from Fig. 7 (reversed picture, detail), unetched, bright field. From left to right: metal (in pink), inner light-grey layer, intermediate brown layer and top dark-grey layer. The area selected for elemental chemical distribution (Fig. 13) is marked by a red rectangle,
Credit HE-Arc CR.
Fig. 12: Micrograph of the same area as Fig. 11 and corresponding to the stratigraphy of Fig. 14, polarized light. From left to right: metal (in brown) covered with a corrosion layer consisting of a black layer, an intermediate brown layer with bright spots, a crack (white line) and a red layer with white particles,
Uniform
lake patina (Schweizer 1994)
None.
NMM1 in binocular mode is not observed in cross-section mode, as the cross-section does not show any coating.
CP1 in binocular mode is documented as sediment (S1) and CP1 in cross-section mode. But it is not clear if it matches the CP1 from cross-section, which is a Fe-rich layer, or if CP1 from binocular mode developed as an atmospheric corrosion after the excavation and is therefore not present on the embedded sample.
CP2 and CP3 in binocular mode match CP2 and CP3 in cross-section mode.
On cross-section, it was possible to describe and analyze the microstructure of the metal.
The tang fragment is made from a leaded bronze and has been cold worked on the top surface after annealing. The SEM/EDS examination and past XRD analyses indicate the presence of chalcopyrite in the corrosion layer, typical of lake context (Schweizer 1994). This corrosion layer is enriched with Sn close to the metal surface and depleted of Cu on the outer surface. The limit of the original surface most probably lies between the Sn-rich inner layer and the Fe and S-rich outer layers. The presence of iron oxides on top of the copper corrosion layer has not yet been explained. The corrosion is a type 1 according Robbiola et al. 1998.
Cet objet a été échantillonné pour la première fois en 1987. Grâce à une importante documentation sur coupe et comparaison avec des objets similaires (voir références), Schweizer définit sur cet objet une typologie "patine lacustre" qui renseigne sur l'environnement de la sépulture. En effet, selon ses recherches, la « patine lacustre » dense, analysée comme de la chalcopyrite, ne peut être générée qu'en présence de bactéries sulfato-réductrices. Les conditions pour ces bactéries sont un environnement anaérobie, humide et riche en S et Fe. Cet objet a probablement été abandonné directement dans le lac
Références sur l'objet et l'échantillon
Fichiers objet dans MiCorr
1. MiCorr_Pin ou fragment d'aiguille HR-3031
2. MiCorr_Tang fragment d'un couteau HR-6246
3. MiCorr_Pin HR-18152
4. MiCorr_Pin HR-17773
5. MiCorr_Pin HR-3071
6. MiCorr_Pin HR-18603
7. MiCorr_Pin HR-3389
Objet Références
8. Rychner-Faraggi AM. (1993) Hauterive – Champréveyres 9. Métal et parure au Bronze finale. Archéologie neuchâteloise, 17 (Neuchâtel).
9. Hochuli, S. et al. (1988) SPM III Bronzezeit, Verlag Schweizerische Gesellschaft für Ur- und Frühgschichte Basel, 76-77, 379.
Échantillon de références
10. Rapport Empa 137 695/1991, PO Boll.
11. Rapport d'examen, Lab. Musées d'Art et d'Histoire, Genève GE, 87-194 à 87-197.
12. Schweizer, F. (1994) Objets en bronze des sites lacustres : de la patine à la bibliographie. Dans : Métaux anciens et historiques, conservation et recherche scientifique (eds. Scott, DA, Podany, J. et Considine BB), The Getty Conservation Institute, 33-50.
Références sur les méthodes analytiques et l'interprétation
13. Robbiola, L., Blengino, JM., Fiaud, C. (1998) Morphologie et mécanismes de formation des patines naturelles sur les alliages Cu-Sn archéologiques, Corrosion Science, 40, 12, 2083-2111.
