Figure 4
Principal component analysis (PCA) of the XRF measurements on the inscriptions. (a) PCA loading plot of the elemental composition (see SI for the list of MPs and their assignments). The yellow ellipse highlights the six points with uniform composition with the largest quantity of detected ink. (b) PCA scores plot of the elements; Fe and Mn are well separated from the rest confirming their high correlation values (R = 0.86). The PC1 in (a,b) is attributed to the amount of ink released during writing. (c) Enlargement of the upper left quadrant of (a): here the MPs are grouped with different polygonal forms. MPs labelled as AI9 and AI10, reported in red colour, correspond to red-appearing areas in the funerary shroud. The black rectangle groups the MPs from the funerary shroud corresponding to the black inscriptions. The green pentagon groups the MPs on the brownish coloured inscriptions, while the red hexagon assembles the brownish coloured spots; the latter is probably connected to the “foxing” damage that is due to degradation processes. (d) Enlargement of (a) around the zero values for PC1 and PC2.
