Plating of archaeological metallic objects - studies by differential PIXE

The differential PIXE method using an external proton beam up to 3 MeV energy was applied to examine plated layers of tin, silver and gold on bronze, brass, iron and silver objects from Roman and Early Medieval period. The concentration profiles were deduced from the measurements by the method of virtual slicing the target into layers, and minimizing the differences between the measured and calculated X-ray yields. The tinned layers were usually thin (about 1 μm), but the thickness of silver and gold layers was in several cases thicker and exceeded the proton range. The plating techniques were identified as application of the molten metal for tinning, and as fire gilding for the gilded objects