This study focuses on the application of a multi-analytical approach combining image processing techniques, imaging studies and material characterisation of a French late fifteen-early sixteen century incunabulum – the BPE, Inc.438. The first study goal was to verify the potential of computational methods in NIR imaging to retrieve accurate reconstructions of the engraving printings by Germain Hardouyn. For this aspect, two representative scenes were chosen: Trinity, f.8r; Saint Anthony the Abbot, f.61v. The applied methodology allowed faster creation of digital reconstructions while the material analysis proved the use of azurite, malachite, vermilion, lead white and ochres, and their NIR response was assessed in the context of the digital processing. The second goal was to make a comparison between chosen illuminations and engraved references of the same representations from two incunabula of the British Library, unravelling the illuminator’s intentional iconographic alteration based on visual and theological criteria.
This paper explores the use of portable Raman instruments to characterise natural dye lakes in paint mixtures, as an alternative approach to other Raman techniques (e.g. SERS). Raman spectroscopy has indeed been used extensively to study natural dyes as pure substances or as artistic pigments (dye lakes). However, the examination of these compounds with Raman spectroscopy is particularly challenging because of a strong fluorescence, a relatively weak Raman signal and their occurrence at low concentrations in artefacts. Because of these challenges, the typical way of analysing these materials is through either surface‐enhanced Raman spectroscopy (SERS) or Fourier‐transform (FT) Raman spectroscopy, yet those approaches are not always desirable in art analysis, especially as they often require micro‐sampling. Therefore, this study explores the potential of using commercial mobile instruments, which would open the possibilities for direct in situ analysis. Two dispersive instruments, one using a fibre‐optic probe and a 1064‐nm excitation laser and the other using the subtracted‐shifted excitation (SSE) post‐processing algorithm, have been tested in their feasibility to characterise dye lakes. Raman spectra were acquired from a set of laboratory reproductions of paint mixtures prepared with a chosen set of common lakes, three red (brazilwood, cochineal and madder) and one yellow (weld), mixed with natural proteinaceous and polysaccharide binders. The feasibility has been evaluated, and it is shown that these lakes produce a detectable Raman signal, in spite of the strong interference of the painting support (parchment) and that the two instruments provide significantly different information.
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