A study on red lead degradation in a medieval manuscriptLorvão Apocalypse(1189)

Abstract

The mechanisms of red lead degradation were studied in a medieval Portuguese codex, Lorvão Apocalypse (1189), by Raman microscopy (µ-Raman) and micro-X-ray diffraction (µ-XRD). The range of pigments found for the illuminations is mainly limited to vermilion, orpiment and red lead. Micro-Fourier transform infrared spectroscopy (µ-FTIR) determined that the pigments were applied in a proteinaceous binding medium. In the red and orange colours, arsenic (As) was determined, by micro-energy dispersive X-ray fluorescence (µ-EDXRF), to be ranging 1-4% (wt %). For those colours, lead white and calcium carbonate were found as fillers whereas orpiment was applied as a pure pigment. Raman microscopy identified, unequivocally, the degradation product of red lead as galena [lead (II) sulphide, PbS].To determine the main factors affecting red lead degradation, a set of accelerating ageing experiments was designed to assess the influence of extenders and of the two other pigments, vermilion and orpiment. The experiments were followed by µ-Raman, µ-EDXRF and XRD. Raman microscopy results for the simulation of degradation of red lead, in the presence of orpiment, are in agreement to what was found in the Lorvão Apocalypse, galena being the main degradation product; also in common is a Raman band at ca. 810 cm −1 , which was attributed to a lead arsenate compound. It was concluded that in Lorvão Apocalypse, the degradation of red lead was a result of its reaction with orpiment.

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

“…This was known to artists and artisans, as demonstrated by the presence of a blank space between yellow orpiment and red lead in a 12th century illuminated manuscript, although mixtures of the two pigments do not behave consistently. The reaction between red lead and orpiment produced galena, which could further degrade into sulphates, and lead arsenate species [241]. Mimetite Pb 5 (AsO 4 ) 3 Cl was as well identified as a reaction product of minium and orpiment [186].…”

“…It is soluble in diluted acids (nitric, chloridric, oxalic, acetic), with formation of the corresponding salts, and when heated it transforms to litharge [1,240]. It is sensitive to sulphur containing compounds, as H 2 S and SO 2 of atmospheric or biological origin, and pigments such as arsenic sulphides (As x S y ), vermillion (HgS) and ultramarine (Na 8 [Al 6 Si 6 O 24 ]S n ), especially in manuscripts, wall paintings, and in case the pigment is not mixed with a binder, which cause the formation of dark grey PbS [1,60,93,124,238,241] and of whitish PbSO 4 [59,68,233,242]. This was known to artists and artisans, as demonstrated by the presence of a blank space between yellow orpiment and red lead in a 12th century illuminated manuscript, although mixtures of the two pigments do not behave consistently.…”

Organic dyes in illuminated manuscripts: a unique cultural and historic record

“…Over the past 10 years, we have contributed to the development of advanced techniques that allow us to characterize and rigorously quantify colour and colour loss in monastic manuscripts from the twelfth and thirteenth centuries [1][2][3][4]. More recently, these studies have also included books of hours as well as other artworks covering a period from the twelfth to the nineteenth centuries [5][6][7][8].…”

Colour identification, degradation processes and findings in a fifteenth-century Book of Hours: the case study of Cofre n.º 31 from Mafra National Palace

“…The matte look of gold powder, observed in elements 5 Galena was identified by Miguel et al [30] as a result of the reaction of orange of minium with orpiment (As 2 O 3 ) found in twelfth century Portuguese manuscripts.…”

“…16d). As an hypothesis for the phenomenon, we proposed the reaction that involves the minium (Pb 3 O 4 ) and hydrogen sulphide in air (H 2 S) producing lead sulphide (II), called galena (PbS) 5 [30], of similar appearance to that of silver sulphide (Ag 2 S). In addition, some studies about this pigment and its degradation raise the hypothesis of the influence of humidity and binders in colour stability, relating its discolouration to an egg white tempera, probably due to the presence of sulfur [31][32][33].…”