The most influential factor is corrosion. Due to the limited penetration depth of
the primary and secondary x-ray signal, the signal reaching the detector from a corroded
archaeological sample is a combination of the corrosion layer and the metal matrix,
depending on corrosion thickness.
Interpreting Archaeological XRF Data 2
Factor 4 Surface Treatment
The surface of a copper alloy artefact may be altered e.g. By surface enrichment,
dipping or plating, surface depletion. The commonest is dipping, e.g. applying a
silver or tin surface to an artefact to change its visual appearance. Due to depth
penetration of the primary and secondary beams the thickness of the surface layer
will make a contribution to the detected signal.