Ion beam characterisation of paint layers made according to late 18th century techniques

External beam particle-induced X-ray emission (PIXE) and PIGE were applied in a study of layered paint structures. A series of layered paint samples were prepared according to known late 18th century techniques. Special attention was paid to two-layer systems with lead white paint as the top layer. The effects of the opaque layer of lead white on the PIXE results were studied and a method for calculating the thickness of the lead white layer is suggested. The interpretation of PIXE results from two-layer systems is discussed in terms of detection limits. Using a 3 MeV proton beam, elements lighter than iron cannot be detected beneath an opaque layer of flake white paint. In the case of calcium the nuclear reaction Ca-48(p,ngamma)Sc-48 can be used as an indicator for a chalk ground beneath the lead white paint. However, a higher proton energy (4.2 MeV) is needed in this case. (C) 2002 Elsevier Science B.V. All rights reserved.