Bust of an applique 2005.054.F00265.1 - Quarternary bronze alloy - Roman Times - Switzerland

Bust of an applique 2005.054.F00265.1 - Quarternary bronze alloy - Roman Times - Switzerland

Bust of an applique 2005.054.F00265.1

Christian. Degrigny (HE-Arc CR, Neuchâtel, Neuchâtel, Switzerland) & Marie. Arnautou (HE-Arc CR, Neuchâtel, Neuchâtel, Switzerland) & Valentin. Boissonnas (HE-Arc CR, Neuchâtel, Neuchâtel, Switzerland)

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Credit HE-Arc CR, M.Arnautou.

Fig. 1: Bust of an applique as found (left picture) and the bust (right picture),

Bust representing a love figure from a bronze applique (Fig. 1), covered by a thin dark-grey patina and scattered green corrosion products. Dimensions: L = 6 cm; W = 3.5 cm; T = 3 cm. 

Applique

Augst BL, Augusta Raurica, Insula 27, Roman villa, Avenches, Vaud, Switzerland

Excavation 2005

Roman Times

Soil

Museum Augusta Raurica, Avenches

Museum Augusta Raurica, Avenches

2005.054.F00265.1

N/A

Complementary information

None.

Credit HE-Arc CR, M.Arnautou.

Fig.2: Location of areas of visual observation in blue, of sampling in yellow and of analyses (XRF) in red,

Credit HE-Arc CR, M.Arnautou.

Fig. 3: Dark patina located on Fig. 2,

Credit HE-Arc CR, M.Arnautou.

Fig. 4: Porous zone located on Fig. 2,

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

Credit HE-Arc CR, M.Arnautou.

Fig. 5: Stratigraphic representation based on visual observation and visualization of the stratigraphies of Figs. 6 and 7.

Fig. 6: Stratigraphic representation of the corrosion structure of the bust observed macroscopically under binocular microscope using the MiCorr application. The characteristics of the strata are only accessible by clicking on the drawing that redirects you to the search tool by stratigraphy representation. This representation can be compared to Fig. 5, Credit HE-Arc CR, C.Degrigny.
Fig. 7: Stratigraphic representation of the corrosion structure of the bust observed macroscopically under binocular microscope using the MiCorr application. The characteristics of the strata are only accessible by clicking on the drawing that redirects you to the search tool by stratigraphy representation. This representation can be compared to Fig. 5, Credit HE-Arc CR, C.Degrigny.

The sample is a scale (1 x 1 mm) of the dark-grey patina taken from the bottom part of the bust (Fig.2).

Quarternary bronze alloy

Hollow cast, chiselled

None

None

Museum Augusta Raurica, Avenches

2013, study of the corrosion layer

Complementary information

None.

Analyses performed:
XRF, SEM/EDS. XRF was carried out with portable X-ray fluorescence spectrometer (NITON XL3t 950 Air GOLDD+ analyser, Thermo-Fischer®, mode "General metal", acquisition time: 20/20/20s).

The entire surface of the bust is covered by a dark grey layer (CP2) directly attached to the remaining metal (Fig. 3). The surface analyses (Table 1) performed on the bust have revealed a high amount of Cu, as well as Pb, Sn and Zn. These are elements which can be constituents of the alloy, while elements in minor amount such as Al, Si and Fe are likely to originate from the environment.

 

Elements mass %

Areas

Cu

 

Pb

 

Sn

 

Zn

 

Si

 

Al

 

Fe

 
1 43 24 13 8 5 3 3
2 52 23 11 6 4 2 2
3 69 17 5 4 2 2 1


Table 1: Chemical composition of the dark-grey patina of the selected areas of Fig.2 (red squares). Method of analysis: HE-Arc portable XRF.

 The metal has not been examinated.

None

Cu

Zn, Sn, Pb

Complementary information

None.

The qualitative analysis carried out on the dark patina by SEM/EDS (Fig. 8) confirms the XRF results (Table 1), showing the same elements and the presence of O, which probably correspond to copper oxide (cuprite Cu2O or tenorite CuO). The dark patina is covered by an adherent green corrosion layer (CP1) which has developed in scattered clusters (probably copper carbonate). The clusters have a surface area of 2 mm2 to 2 cm2, and have a thickness of 0.5 to 5 millimeters. In some places, the green corrosion layer has formed in the porous blisters of the dark layer (Fig. 5). Charcoal might be found locally (POM1) as well as different sediments: S1 (discontinuous and brown), S2 (mixed with fine and coarse sand grains) and S3 (scattered homogeneous brown layer).

Credit HE-Arc CR, M.Arnautou.

Fig. 8: EDS spectrum of the scale of the dark-grey patina taken from the bottom part of the bust (yellow arrow of Fig. 2),

Multiform

Type I (Robbiola)

Complementary information

None.

None.

The metal is probably a quaternary bronze (Cu-Pb-Sn-Zn) according to the qualitative XRF analysis performed on the surface of the bust. The high amount of lead is probably due to its diffusion towards the metal surface caused by exposure to high temperatures. The dark patina (CP2) has developed from a smooth layer to voluminous green crusts (CP1) corresponding to a type 1 corrosion according to Robbiola and al. 1998. The artefact has been excavated from a burial context characterized by burnt soil, which could explain the formation of the black patina (tenorite will form at temperatures above 300/400°C). A green corrosion has developed in the porous blisters of the dark layer. The limit of the original surface is located at the interface of the dark smooth corrosion and the green adherent corrosion product. In certain areas the limit of the original surface has been elevated from its original position.

References on object and sample

References object

1. Pfäffli, B. (2005) Ausgrabungen in Augst im Jahre.

2. Künzl, E., Künzl, S. (2003) Das römische Prunkportal von Ladenburg, Stuttgart.

 

References on analytic methods and interpretation

 

3. Robbiola, L., Blengino, J-M., and Fiaud, C. (1998) Morphology and mecanisms of formation of natural patinas on archeological Cu-Sn alloys, in Corrosion science. Vol. 40, n° 12, 2083-2111.

4.  Scott, D.A. (2002) Copper and bronze in art: corrosion, colorants, conservation, Los Angeles.