*3.9. Yellow and Yellow-Brown Pigments*

The set of FORS spectra collected throughout the manuscript were mainly characterised by sigmoid-shaped spectra with points of inflection within 480 and 560 nm. According to this feature, four different yellow colourants could be hypothesised after the FORS survey and the use of the other techniques allowed us to confidently identify the following yellow pigments.


**Figure 8.** (**a**) Micro-photography (80×) of the golden architecture on f. 1r. (**b**) Micro-photography (80×) of the glittering details on the rock painted in the picture background on f. 15r (Figure 1b).

The FORS spectrum showed an inflexion point at ca. 530 nm, which is consistent with the feature of mosaic gold (also called purpurin–SnS2) [24], a well-known substitute for gold which is typical of medieval miniature painting. XRF analysis confirmed the presence of tin and sulphur, as did the micro-Raman analysis that yielded spectra showing a very intense peak at 321 cm−<sup>1</sup> (Figure 9).

**Figure 9.** Raman spectrum obtained from brown-yellow areas revealing tin sulphide.

The Raman spectra of Sn(IV) sulphide reported in the literature [29] shows an intense signal at slightly lower frequency (313 cm<sup>−</sup>1), therefore one can assume that different recipes could yield different molecular structures that may give slightly different Raman responses.

4. Finally, finer glittering particles were identified by XRF as gold; these areas also yielded a FORS spectrum with the typical inflexion point of gold at ca. 505 nm [24]. Powdered gold was used here, in the same way as other pigments, mixed with a medium and spread as a thin film with a brush; since the "ready to use" pigments were generally kept in shells, this technique is referred to as "shell gold", to distinguish it from the gold leaf technique, in which a very thin leaf of gold adheres on the vellum by means of an adhesive [30].

In the page borders decorations, the large yellowish leaves were obtained by spreading a thin layer of shell gold.

Gold was also employed for the haloes, executed using the gold leaf technique. In these areas XRF analysis also revealed calcium, sulphur and weak signals of copper and iron, in addition to gold. These traces of copper and iron are possibly related to impurities in the gold leaf while the high XRF signals from calcium and sulphur, significantly higher than those obtained from the unpainted parchment, indicate the use of gypsum in the typical *asiso* ground for gold, used in the Middle Ages starting from the 13th century [30].
