Fig. 3

Graphical representation of methodology on historic fragments. Red and black arrows = work carried out in this research and blue arrows = previous work carried out by McCullough (unpublished). a Example of a historic tapestry fragment where yarns removed in earlier work for NIR are denoted as “1”. Yarns removed for FTIR analysis in this research (“2”) were adjacent to previous yarns in “1”. b 3 spectra were recorded per measurement for “1” yarns and averaged for each yarn, c averaged raw NIR spectra for 5 yarns, d 5 adjacent yarns in “2” were unravelled and cut to approximately 0.5 mm, with 3 FTIR spectra recorded for each piece from one yarn and averaged, e averaged raw FTIR spectra of 5 yarns from area “2” adjacent to “1”. f Multivariate analysis = principal component analysis and cross validation experiments, g validation of model on validation sets (known oxidation ratios) and independent set (unknown ratios)