The fading of red lead pigment in wall paintings: tracking the physico-chemical transformations by means of complementary micro-analysis techniques

On the stability of mediaeval inorganic pigments: a literature review of the effect of climate, material selection, biological activity, analysis and conservation treatments

“…Moreover, it seems that minium promotes the blackening of leadwhite, when the pigments are mixed [204]. Some cases of red lead lightening are reported as well, and are related to the formation of lead sulphates and/or carbonates, according to the atmospheric pollutants and to the initial amount of PbO in red lead [68,93,200,237,238], via the formation of plumbonacrite [228].…”

“…Red lead, or minium, has a long history of use in worldwide artistic and artisanal practices, although nomenclature issues are evident [1,237,238]. Its synthesis and relation with the other lead oxides is well described in literature [238].…”

“…A role of Cl − ions is also hypothesized [93,245]. The formation mechanism of black discolouration products [plattnerite (PbO 2 ) and galena (PbS)] was recently investigated: no plattnerite could be detected in artificial ageing tests, while the natural ageing of fresco red lead samples yielded calcite CaCO 3 , minium Pb 3 O 4 , plattnerite PbO 2 , anglesite PbSO 4 and gypsum CaSO 4 ·2H 2 O, with the minium grains being gradually converted to alteration products (plattnerite and anglesite) via a sulphation step followed by solvolytic disproportionation [237,242]. Plattnerite might be formed if acidic pollutants attack the paint layer [242]; or when biological colonization is present [238].…”

Nondestructive Raman investigation on wall paintings at Sala Vaccarini in Catania (Sicily)

“…Finally, it needs to be noticed that the presence of Pb sulfates (anglesite, PbSO 4 ) might point out the ongoing red lead alteration process due to atmospheric SO 2 [11]. In fact, as evidenced by recent researches [12][13][14], such secondary phase is occasionally detected on discolored red lead [15], even if this soluble lead salt may be often leached during aging in humid conditions.…”

A comparative study of wall paintings at the Cypriot monastery of Christ Antiphonitis: one artist or two?

“…Minium chemical alteration occurs under different weathering conditions such as effect of temperature, light, atmospheric pollutants SO 2 and CO 2 , micro-organisms, etc. (Aze et al, 2006). Not to be ignored is the fact that another gradual alteration of orange minium from Pb 3 O 4 to white cerussite PbCO 3 and/or anglesite PbSO 4 can be seen in wall paintings of other historical monuments (Barbu and Mohanu, 2006;Sotiropoulou et al, 2007); however no indication of these phenomena has been noted in the Antiphonitis fragments.…”