Many of the materials identified during the analyses were used by most of the artists; this is in no way surprising, considering that 15th-century illuminators had a relatively small range of pigments at their disposal. Table 1
summarises the results of the analyses, the most interesting of which will be discussed in detail in the following sections.
The shared palette included malachite, used as a green pigment in all the analysed manuscripts. Vermilion was also used extensively, as was an organic red colourant, likely insect-based, which was mixed with lead white to obtain a range of pink hues. No evidence for gypsum mixed with the red dye was found. Lead-tin yellow was the only yellow pigment found in the manuscripts. Whenever Raman analyses were performed, this was found to be lead-tin yellow type I. Most brown areas were painted with complex and diverse mixtures of earth pigments, vermilion, indigo and red lead. Flesh tones were usually found to contain lead white and vermilion; the presence of additional pigments such as earths and ochres could not be proven in most cases but cannot be conclusively excluded. Mosaic gold (tin disulphide) was only identified in four of the manuscripts, whereas every single volume contains gold leaf. The composition of the underlying ground layer (‘bole’) could only be analysed occasionally, as the well-preserved gold leaf did not usually allow direct access to the bole. When data were successfully acquired, the bole was found to be traditionally composed of gypsum and a red earth or clay. In some cases, vermilion was also identified in the bole. A detailed analysis of the inks used to write the text was outside the scope of this research; however, inks were briefly tested in each manuscript and found to be traditional iron-gall inks.
There is great variety amongst the manuscripts in the use of blue pigments, which deserve further discussion and serve as a good example of the importance of employing a multi-technique approach. Three different blue pigments were identified, for example, in folio 32v of Antiphonary M (Figure 2
a). As seen in the NIR image (Figure 2
b), the green initial and leaves appear dark, suggesting the use of a copper-based compound. Most of the blue background inside the initial appears light, excluding the presence of azurite. Some areas close to the saint’s figure and the scroll however appear dark, meaning that azurite might have been used selectively. These observations are supported by the XRF maps (Figure 3
a); the K-Kα map suggests the use of ultramarine in most blue areas (no cobalt was identified, therefore the presence of potassium could not be due to smalt), whereas the Cu-Kα map shows how azurite was used for outlining and shadowing. The light blue leaves in the upper-right and bottom-left corner of the initial are visible in both maps, suggesting a mixture of ultramarine and azurite. This is reflected in their appearance in mid-grey tones in the NIR image. FORS analysis (Figure 3
b) confirms the identification of the materials mentioned above and provides additional information, for example by proving the presence of indigo (max absorption at 660 nm), mixed with lead white (absorption bands at 1447 and 2321 nm), in the shadowed areas of the white scroll held by the saint. Raman analysis (Figure 3
c) confirmed that indigo was also used in the muddy-green landscape (peaks at 545 (w) and 1572 (w) cm−1
), in a mixture with lead-tin yellow. The latter pigment (peaks at 128 (vs), 195 (m), 270 (w) and 454 (w) cm−1
) also provided highlights in the saint’s rainbow-coloured robe.
3.2. Illuminations Attributed to Cristoforo Cortese
All the miniatures in the two San Giorgio manuscripts attributed to Cristoforo Cortese (Psalter N and Missal CXII) have a shared palette which includes azurite, lead white, an organic red colourant (likely insect-derived) mixed with lead white, mosaic gold and carbon black (used for outlines). Malachite is the main green pigment, used in all the miniatures. On folios 99r and 150r of Psalter N, malachite is mixed with azurite, yielding a slightly different shade of green.
A significant visual difference within the numerous miniatures in Psalter N regards the orange and red areas. Some of the miniatures are characterised by bright orange layers, highlighted with thick yellow and white brushstrokes (Figure 4
a,c). Others, instead, have a slightly more sombre palette, with darker red hues dominating, and thin white highlights only (Figure 4
b,d). We could only identify two cases in this volume, where orange was painted over red (in folios 7v and 36r, see Figure 4
e). FORS and Raman analyses (Figure 5
a,b) confirmed the use of vermilion and red lead for the red and orange areas, respectively. Vermilion was identified by its transition edge around 605 nm in the FORS spectra and by Raman peaks at 254 (s) and 345 (m) cm−1
. Red lead showed its typical 570 nm transition edge and Raman peaks at 121 (vs), 142 (s), 223 (m), 310 (m) and 548 (s) cm−1
. The presence of additional peaks at 286 (s) and 388 (s) cm−1
, together with the unexpectedly high intensity of the peak at 142 cm−1
suggest the additional presence of massicot. The latter is often found alongside red lead in historic manuscripts, either as a residue of the roasting process of the lead-based red pigment, or as an impurity of the natural lead tetroxide mineral minium.
Missal CXII, whose illuminations are also attributed to Cristoforo Cortese despite the obvious overall stylistic differences (see Figure 6
), does not contain any orange areas; vermilion alone was identified in all red areas analysed in the manuscript.
3.3. The Identification of Smalt in Miniatures Attributed to the Master of Antiphonary Q
Nine of the miniatures analysed are attributed to the Master of Antiphonary Q; four of them are included in his eponymous manuscript, whereas the remaining five are spread across five additional volumes (see Table 1
). Overall, a shared palette was indeed identified within the miniatures present on these folios. It includes ultramarine, vermilion, lead white, malachite, as well as lead-tin yellow type I. The latter is often also mixed with malachite in green areas and used to outline and highlight red areas. None of the miniatures contain red lead. Gold leaf was used extensively, whereas shell silver appears to have only been used to depict a light grey fish in folio 7v of Antiphonary Q. The results presented here focus on the miniatures rather than on the decorative borders, also present on the same pages, which were likely executed by workshop assistants and therefore have no bearings on the attribution to the Master of Antiphonary Q.
NIR imaging reveals some differences among the nine miniatures, two of which are shown in Figure 7
and Figure 8
as an example. In Antiphonary Q, folio 5v, the infrared image reveals little or no underdrawing. In Antiphonary M, folio 8v, however, NIR imaging reveals the likely presence of underdrawing, traced with a dry medium, as well as the presence of cross-hatching—used to indicate modelling—in the shadows. This is especially visible in the Virgin’s dark pink robe. These observations may suggest that the miniatures were designed, if not painted, by two different artists.
Additional differences were observed in the use of blue pigments within the miniatures, especially in light blue areas. Pure ultramarine was identified in these areas, in the four miniatures within Antiphonary Q, as well as in the image on folio 1v within Antiphonary R. In the other four images, however (Antiphonary M, folio 8v; Antiphonary q, folio 2v; Gradual B, folio 27v; and Kyriale AE, folio 65v), light blue hues contain a mixture of smalt and ultramarine. The combined presence of both blue pigments is confirmed by two of the three spectroscopic methods employed. In the Virgin’s blue mantle depicted on folio 8v of Antiphonary M (Figure 7
a), for example, FORS spectra of all blue areas (Figure 9
a) display a narrow peak with maximum at 460 nm, in addition to ultramarine’s typical deep absorption centred at 600 nm, followed by a sharp increase in reflectance. Uncharacteristically for ultramarine, however, reflectance drops again around 1200 nm. This suggests the possible presence of a cobalt-containing pigment, which is confirmed by the elemental map for cobalt, obtained by fitting the Co Kα XRF peak at 6.9 keV (Figure 9
b). Smalt’s typical absorptions at 545, 600 and 640 nm can only be detected in the reflectance spectra of the lighter blue areas. This information, coupled with the slight differences between the elemental maps for cobalt, potassium, iron and calcium (see Supplementary Materials
), reveal that the dark blue brushstrokes used to model the mantle contain ultramarine alone. Incidentally, the Virgin’s mantle is also the only blue area within the Master of Antiphonary Q miniatures, which also contains small amounts of azurite, as revealed by weak absorption bands at 1495, 2285 and 2354 nm in the reflectance spectra (Figure 9
a) and by widespread low signal for copper in the elemental maps (see Supplementary Materials
Raman analysis of the blue mantle confirms the presence of ultramarine alone, characterised by a sharp peak at 548 (s) cm−1
c). The challenges of detecting smalt in ultramarine mixtures non-invasively are well known: smalt is difficult to detect by Raman spectroscopy, especially with a portable system equipped with a NIR source [8
] and it is only detected by FORS if present in relatively high amount [10
]. The most reliable way to confirm its presence, even in very small percentages, is to use XRF spectroscopy, which can easily detect small amounts of cobalt. On the other hand, ultramarine is efficiently detected by Raman, but not easily picked out by FORS in a mixture with smalt, due to similar and not particularly specific spectral features. Similarly, ultramarine can go undetected through XRF analysis when smalt is also present, since the detectable elements (aluminium, silicon and potassium) are present in both pigments. To conclusively identify both components in a mixture of smalt and ultramarine, it is imperative to use a multi-analytical approach [10
3.4. The Identification of Metallic Bismuth in Decorative Borders
Decorative borders with thin black lines having a metallic appearance are present in seven out of the eight folios analysed with miniatures attributed to the Master of Antiphonary Q (see Figure 10
a). The only exception is the large scene with the Visitation of the Virgin in Antiphonary M (Figure 7
XRF mapping detected the characteristic X-ray lines of bismuth (Bi: Lα at 10.84 keV, Lβ at 13.02 keV). These could be clearly distinguished from the lead lines (Pb: Lα at 10.55 keV, Lβ at 12.61 keV), which have a completely different spatial distribution (Figure 10
b). Raman spectroscopy (Figure 10
c) identified the material as a metallic bismuth, with its characteristic peaks at 94 (vs) and 185 (m) cm−1
]. Under magnification (Figure 10
d), these lines appear silvery grey with a reddish or pinkish iridescence, similarly to what has been observed by other scholars [11