Analyses performed:
Metallography (Nital etched), SEM/EDS

Based on the analyses carried out, the schematic representation of the stratigraphy of corrosion layers was corrected (Fig. 14). The following strata were identified:

S1 = sand-clay soil, compact, cemented when dry, powdery when abrazed, very thin particle size (usually about and less than 0.1mm). Undefined thickness (soil).

CP1 = powdery orange (loosely coherent) and matte corrosion crust, sometimes forming humps. Partially mixed with S1 and POM layers (diffused interfaces). 1 to 5 millimeters thick.

CP2 = vivid red or pink dots, more brittle than powdery (loose cohesion) and mostly matte, only two or three observed, always above CP3 interfaces. Usually 1 mm spheric diameter.

CP3 = dark reddish corrosion product, forming smooth, matte and brittle layers that are parallel to CP4, with a clean and regular interface. The corrosion products are generally hard, but sometimes break up into grains, resulting in a more irregular interface. The layer is approximately 0.5mm thick.

CP4 = dark grey to black corrosion product, smooth with pseudo-metallic reflection (a bit glossy), very hard, when scratched results in orange powder, with somewhat irregular shape and thickness (ranging from 0.3 to 2mm).

CP5 = dark grey to black corrosion product, generally a bit darker than CP4. Smooth with pseudo-metallic reflection, even harder than CP4 and when scratched it turns into an orange coloured powder. Irregular interface regarding CP4. Clear transition and somewhat parallel from CP4 to CP5. As regards its thickness, it fills the remaining volume.

NMM = silica and calcareous inclusions.

POM = mostly powdery and grain-like material, ranging from orange to dark brown in colour, somewhat glossy and similar to crystals when illuminated. A few fiber-like zones are present, which are more satin than glossy. They are dark brown to charcoal black, very brittle and break into a powdery and grain-like material. POM is located above or close to CP3 and CP4 layers, sometimes mixed into S1 or CP1 layers with a diffused interface. Overall, the stratum is approximately 0.2-0.3mm thick.

SV = structural void, present as fissures that either pass through the different layers, or are present at corrosion interfaces, especially at the CP4/CP5 interface. The void is 0.1 to 0.3mm thick and partially filled with POM in the outer layers.

M1 = glossy with metallic reflection.

The nail is apparently made of a hypoeutectoid steel, with what may be a pearlite phase. Roman shoe nails are forged and pushed through leather soles by hammering them against a hard foot-shaped buckering device. This requires the steel to be strong, but not too brittle, otherwise it will be prone to breaking when pushed through the soles or when in use for marching on hard surfaces. This nail is almost entirely mineralized. Its original shape seems however to be preserved within the corrosion layers. In addition to this, what appears to be leather fibers seem to be preserved in either mineralized or organic form.