Raman microspectroscopic analysis of pigments of the Gothic wall painting from the Dominican Monastery in Ptuj (Slovenia)

Abstract

The study deals with the characterization of pigments from the newly discovered wall painting at the Dominican Monastery in Ptuj (Slovenia) in order to acquire detailed information about the technology used, as well as to identify the deterioration products. The uncovered wall painting, depicting a vivid procession of riders, is dated to the late 14th century. Painting techniques and pigments were analysed by optical microscopy and Raman microspectroscopy. The optical microscope revealed that the wall painting was executed in a lime technique characteristic of the Central‐European artistic expression. Several natural and synthetic inorganic pigments, such as azurite, red and yellow ochres, cinnabar, red lead, lead white, lime white, lead–tin yellow type I and carbon black were identified. Surprising identification of the type I of lead–tin yellow used already in the 14th century is of high importance, since, until now, it was considered that it appeared on the market only in the first half of the 15th century. Plattnerite was observed as a result of degradation of lead pigments. The use of expensive azurite and cinnabar could indicate a wealthy client. Copyright © 2014 John Wiley & Sons, Ltd.

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

“…Synergy with photodegradation and oxidation [64,66] Involved in discolouration and sulphation [106,197,199,202,203,[207][208][209] Unstable [103,123,200], but still used in wall paintings [73,193,[201][202][203] Red Red lead…”

“…It was already known to Romans [195,196] that mercury sulphide darkens when exposed to light, although not systematically [1,193,194,[197][198][199]. Moreover, HgS was not recommended for use in fresco, as humidity and pH affect its stability [103,123,200], but still it was used on wall paintings [73,193,[201][202][203]. Paint layers of pure vermillion are very vulnerable [199], while no darkening is observed when it is mixed with leadwhite [19,20,193,204].…”

“…Lead pigments are not suitable for use in fresco, but they were still used due to their good hiding properties and to the low prices compared to other pigments [5,123,200,[211][212][213]. The degradation processes of the various Pb pigments yield a range of compounds which cause discolouration, strongly affecting the readability of the polychromy [200].…”

“…The degradation processes of the various Pb pigments yield a range of compounds which cause discolouration, strongly affecting the readability of the polychromy [200]. Lead pigments on ceramic artefacts are sensitive to sulphur containing pollutants, to acidic solutions (rain; CO 2 ; microbial activity), to light and air: anglesite PbSO 4 , cerussite PbCO 3 , hydrocerussite 2PbCO 3 ·Pb(OH) 2 and lead sulphide PbS are formed [166].…”

“…Lead dioxide formation is favoured in humid alkaline conditions, such as in frescoes, when peroxides are produces, either by microorganisms or by photo-oxidation of organic materials [213]. When exposed to salt solutions, and light, the most stable phase for all the lead pigments is cerussite [123,200,218]. In oil, lead compounds were not only used as pigments, but as siccatives as well [219,220].…”