The schematic representation below (Fig. 3) gives an overview of the corrosion layers encountered by visual macroscopic observation.

The metal is a grey cast iron with characteristic graphite flakes (Fig. 8). It contains C in addition to P, Mn and some Si (Fig. 9). Its matrix consists of a P-rich eutectoid and a dendritic phase; the latter containing a significant amount of C, but less P than the aforementioned eutectoid (Table 1).

The metal is covered by a coating of alternating layers of paint (appearing light grey, black and bright orange under polarized light, NMM1-NMM3 in Fig. 10). Punctual analyses by SEM-EDS (Table 2) as well as elemental mapping (Fig. 12) reveal that the light grey layer (NMM1) contains a considerable amount of Ba in addition to S, Si and Al. The black layer (NMM2) contains Fe, Si, Mg and Al. The latter is visible as rectangular flakes (see NMM2 in Fig. 11). This layer could consist of Al flakes and FeO in an organic binder (C and O). The underlying, bright orange layer (NMM3) contains Fe and O in addition to a considerable amount of Pb, some Si, Zn and Ca. This layer is probably a preparatory paint consisting of red lead (Pb3O4) and Zn oxide (ZnO). C and O were detected in all layers and are probably components of the binder (Table 2 and Fig. 12).

Furthermore, punctual analyses were carried out in order to determine the chemical composition of the paint flake. Three punctual analyses were carried out for each colour (light grey, black and orange in Fig. 5). The colours correspond to the paint layers previously mentioned, but their composition is slightly different (Table 2, Table 3):
- The light grey layer (similar to NMM1) contains Pb, C and O. Its composition is significally different from NMM1 as it contains neither Ba, S or Al.
- The black layer has a similar composition to NMM2 (C, Fe, O and Al).
- The orange layer is even more rich in lead than NMM3 and contains Ba. This layer is probably a preparatory layer of red lead (Pb3O).

Table 1: Chemical composition of the metal. Method of analysis: SEM-EDS. Lab. of Electronic Microscopy and Microanalysis, Néode, HEI Arc, credit MiCorr_HEI Arc, C.Csefalvay.

Table 2: Chemical composition of the paint layers attached to the metal sample (Fig. 4). Method of analysis: SEM-EDS. Lab. of Electronic Microscopy and Microanalysis, Néode, HEI Arc, credit MiCorr_HEI Arc, C.Csefalvay.

Table 3: Chemical composition of the paint layers from the paint flake (Fig. 5). Method of analysis: SEM-EDS. Lab. of Electronic Microscopy and Microanalysis, Néode, HEI Arc, credit MiCorr_HEI Arc, C.Csefalvay.   

The metal is covered by a thin graphitized layer (CP1) as well as a corroded metal phase (CM1). The later is located just beneath NMM3 and appears dark grey under polarized light (Fig. 10). It consists mainly of Fe and O with Pb and Ca (Table 4, Fig. 12). Pb can probably be explained by the proximity to the Pb-rich paint layer NMM3 (Table 2). The presence of Ca is more interesting however, as it might originate from past exposure to the environment, implying that the paint was not applied immediately after fabrication. The composition of CP1 was not analyzed.

Table 4: Chemical composition of the corroded metal phase (CM1) from Fig. 10. Method of analysis: SEM-EDS. Lab. of Electronic Microscopy and Microanalysis, Néode, HEI Arc, credit MiCorr, HEI Arc_C.Csefalvay.