# The Role of PIXE and XRF in Heritage Science:
## 3 PIXE: From Point Analysis to Elemental Maps: An Example  
At the INFN-LABEC, the PIXE technique was employed for many works of art. One of the earliest case studies was the study of the inks of [PERSON]'s handwritten letters, for determining their chronological order by studying their elemental composition [33; 34]. One of the works of art, presented here, is a parchment, a bifolio originally belonging to an antiphony. It contains a musical notation composed of a system of six tetragrams on each page, with neumes and the text of the chant. It is decorated with calligraphic initials and a figured illuminated letter. Details of the irradiated areas are presented in Figure 1. Measurements were carried out to characterise the elemental composition of the pigments of the inks. At the time, the X-rays emitted were detected by two Si(Li) detectors, whose absorbers and whose distances from the sample were chosen so that one was primarily sensitive to elements lighter than \(Z=25\) and the other to heavier elements. Helium flux was continuously flown in front of the measuring set-up for minimising the argon K-lines production from the atmosphere and to reduce the absorption of low energy X-rays. The proton current was of the order of a few hundred pA and the energy around 3 MeV; typical acquisition time ranged from a few seconds to a few minutes, with no risk of damaging the target. The proton beam intensity was monitored by rotating a stage with a thin nickel surface layer regularly through the beam and measuring the nickel K X-rays. For what concerns the pigments, blue and red areas were characterised by the presence of copper and mercury, respectively, suggesting the use of azurite [35], and of cinnabar/vermilion [36]. The PIXE spectra of the yellow areas showed the presence of tin, lead, and a significant amount of silicon. After correcting for self-absorption of X-rays within the paint layer, the measured atomic ratio Pb:Sn:Si approximates to 1:0-25:0-65, a result that suggests the presence of lead-tin yellow of type II, Pb(Sn, Si)O\({}_{3}\). This result allows an indirect dating of the miniature since, from studies of lead-tin yellow samples from Italian paintings of the fourteenth and fifteenth centuries, the transition from the use of type II to type I (Pb\({}_{2}\)SnO\({}_{4}\)) had taken place in Italy around the second quarter of the fifteenth century, as stated in [37]. Figure 1: Areas in which PIXE measurements were performed. The atomic ratio of lead-tin yellow detected here is compatible with type II. Therefore, determining which of these was used may indicate, in a non-destructive and non-invasive way, a _terminus ante queen_ the miniature was painted. Green areas showed the presence of copper, lead, tin, and silicon. The Pb:Sn ratio is the same as that in yellow areas. This result led to the hypothesis that green was obtained by mixing lead-tin yellow and a copper-based pigment, such as blue azurite or green malachite [35]. Further information on this study is included in [38]. An improvement for scanning an area of the target was achieved using two motor stages (Micos KR-33) and a home-made software for the acquisition. The system was based on continuous motion of the target in the plane perpendicular to the beam direction designed and developed for the beamline, as presented in Figure 2. Furthermore, a software for the analysis was developed in-home. The spatial distribution of the elements in an area of a few cm\({}^{2}\) was obtained by recording the spectra for each position and selecting the corresponding energy peaks. The spiral was the scanning mode used since it brings some fundamental advantages. There is no periodical sharp direction change that would impose high acceleration to the sample as in each strip of a raster scan, and the time spent by the beam on each position is rather uniform. The motors complete the first spiral anticlockwise, then stop and retrace the same trajectory clockwise, returning to the initial position. The whole path is inserted in a loop.