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ARTICLES > Material Studies1686
An Alteration Phenomenon of Cinnabar Red Pigment in the Mural Paintings from Sucevita
Introduction
The mural paintings from northern Moldavia have always been a point of interest for specialists in conservation, due to their technical qualities that assured their preservation over the years in the severe climate of this region in Romania. Over the years, both exterior and interior paintings showed colour alterations caused by environmental factors like atmospheric deposits, humidity and light among others. Through physical, chemical or biological processes, these factors induced superficial chromatic alterations of the colours, modifying the artistic expression of the paintings. These alterations are generally considered as patina. The term patina, according to Paul Philippot1, is attributed to the modifications that occur in normal conditions in the colour layer under the action of the previously mentioned factors. When the painting materials are submitted to environmental factors which take course at high intensities on long time periods, we deal with other alterations which can not be considered as patina anymore. Some of these alterations made the subject of a previous paper2. The conservation works started in 1989 by Oliviu Boldura and Tatiana Pogonat gave us the possibility to perform a detailed scientific research on the exterior and interior mural paintings. Even from the beginning our attention was drawn to the phenomena of alteration of pigments in these paintings from which here we shall focus on the alteration of cinnabar red. In a first phase, while analysing the state of conservation of the paintings from the church’s dome, we observed significant surfaces coloured in red having dark aspect and turning into black-brown. Ulteriorly, once the conservation works were started, the same phenomenon could be observed as well in other compartments of the church. The visual inspection and the first cleaning tests led to the conclusion that we do not deal just with common dirt deposits but with a colour alteration. Literature mentions the alteration of cinnabar (red) into metacinnabar3 (black). The same phenomenon is mentioned in the painting manuals of the old masters. Cennino Cennini4 described the alteration of cinnabar as follows: “bear in mind that it is not its nature to be exposed to the open air; it is more lasting on panels than on walls, because, by long exposure to the open air (all’ aria) it becomes black when applied to walls”. Dionysius of Furna writes in his manual (Erminia)5: “[…] as for the cinnabar, when you want to paint outdoors in a place with wind, you should give up, because it turns black while the white must have a high concentration; when you want to paint indoors you should add some ceruse6 and Constantinople ochre and like this it won’t turn black”. The old masters had already noticed the phenomenon, without knowing exactly what causes it and still recommended the use of cinnabar for interior and panel paintings, “in order to keep it away from air and wind”. The exact explanation of the phenomenon was given later afterwards. The mercury sulphide presents two enantiomorph states: a red one, stable, crystallised in the hexagonal system known as cinnabar7 and very appreciated in painting, and a black one, metastable, crystallised in the cubic system or in amorphous state, known as metacinnabar (polymorphism). After a long exposure to solar light, the cinnabar red turns into black metacinnabar. The change takes place through the absorption of a light radiation of 400 to 570 nm wavelength. The alteration is only superficial, under the black layer being the unaltered red. A similar process occurred in the paintings from Suceviţa, thus we proposed to prove that the red pigment and the alteration product are indeed mercury sulphides.
Image 1. General view
of the church, east facade; Image 2. Altar, east apse and triumphal
arch; Image 3 and 4. Nave, dome, Prophet David. Sampling area. Images
during the conservation of the painting.
Methods and materials
The analysed samples were taken from both the red and the superficial overlayer of black colour from the paintings in the dome of the church (sample no. 1, 1st scene, garment of Prophet Solomon and sample 14, 2nd scene, red frame between the scenes) (see images 3 and 4).
The first data were obtained by microscope examination with reflected light. In the cross section no. 329 (90x) from image 5 can be observed the presence of a 5μm thick black layer and a 25μm thick red layer.
For the chemical analyses, the samples were dissolved in aqua regia (a mixture of HCl and HNO, 2:1, v/v). Hg2+ ion was microchemically identified as mercury tetrathiocyanatocobalt8 (blue crystals, CoHg(SCN)4, which belong to the rhombohedral system) (see image 6) by comparison with HgCl2 (reference substance) and by the reduction of Hg2+ to metallic Hg on the copper lamella, which makes a deposit similar to a silver mirror.
The obtained results were verified also by X-ray Diffraction (XRD), using a Dron 2.0 equipment and the working parameters:
- Cu Kα radiation; 36 KV, 20 mA, Ni filter; - angle range 2θ, goniometer speed 4°/’, - cinnabar ASTM 6 – 256, metacinnabar ASTM 6 – 261 The obtained spectrum is shown in figure 1 that shows the presence of both forms of mercury sulphides.
Image
5. Sample no. 329. Cross section (90x) showing a 5μm thick black layer
of metacinnabar and a 25μm thick red layer of cinnabar; Image 6.
Microchemical identification of the mercury tetrathiocyanatocobalt -
CoHg(SCN)4; Figure 1. Spectrum obtained by XRD, showing the presence of
both forms of mercury sulphides: - cinnabar HgS ASTM 6 – 256, -
metacinnabar HgS ASTM 6 – 261.
The chemical reaction has shown crystals of the same shape, colour and size for both the samples and the reference substance. This allows us to state that the analysed samples contain mercury sulphite (cinnabar, metacinnabar, HgS). The metacinnabar presence was confirmed by XRD. The initial hypothesis was confirmed. This is the first case in Romania of mural paintings presenting an alteration of cinnabar. At Suceviţa, the cinnabar red pigment was used in many scenes from all the compartments of the church. It was applied according to the Byzantine technique, on a fresh plaster made of lime and hemp fibbers. The alteration took place not only in the dome’s paintings, but also on scenes from the nave, narthex and exonarthex, on the walls exposed to solar light through the rather large windows. The dome, with an interior diameter of 3.64 m is fully exposed to solar light due to the four 1.83 m windows. The affected surfaces correspond precisely to the strongly lightened areas. A graphic representation of the surfaces from the dome is presented in figures 2 and 3. In the summer of 2007, together with the coordinator of the conservation works Prof. Oliviu Boldura, our research extended to other compartments of the church and to the areas in undergoing work. The cinnabar red did not suffer any alteration in areas where the sun light did not reach. In the nave, due to the six windows symmetrically disposed in the north and south apses (three windows in each), we can observe the paintings from the intradoses and jambs suffered a progressive and differentiated alteration of cinnabar red pigment. A first observation is that the alteration is more obvious in the windows of the south apse, where the sun is stronger in the morning. A differentiated degree of alteration can be seen in each of the three windows, progressive from east to west. Moreover, the west side of the windows was clearly more exposed to sun, thus the paintings from the west jambs are more altered then the ones from the east. A detailed analysis of a scene9 shows the transformation process or cinnabar red pigment. In near proximity of the window can be seen that cinnabar turned into dark-grey and black, the drawing lines applied with ochre-red becoming visible (see image 8 and 9). Next garment painted with cinnabar is located at 0.5 m distance from the window, thus here only a slight alteration to black can be seen (see image 10). The alteration is superficial so it is still possible to see the original red colour. Proceeding to the inside opening of the jamb we notice the alteration becomes discontinuous, insular and the red is much better preserved (see image 11). In the narthex we meet a similar situation but a more pronounced alteration, due to the wide size of the windows and their large opening angle. Here the alteration occurred not only at the jambs of the windows, but also on the north and south walls, especially in the inferior parts. In the exonarthex, due to the three wide windows from the west wall and the two lateral doors that are permanently open, important areas where cinnabar was used were affected by light. A similar case was mentioned in literature at a late Byzantine church from Cyprus10, where the light penetrated through a window and produced on the lightened areas the darkening of the red pigment from a repainting of a interior decoration frame.
Image 7. Nave, south apse, jamb of the west window. The direct action of sunlight over the mural paintings; Image 8. Nave, south apse, jamb of the west window. The differentiated alteration of red cinnabar; Image 9, 10 and 11. The conservation state of the cinnabar red on various surfaces located at different distances from the window (9 - Strong alteration of cinnabar red, 10 - Alteration of cinnabar in a smaller degree, 11 - Areas where cinnabar is well preserved); Image 12. Narthex, north wall, inferior level, scene from the life of St. George; Image 13. Narthex, north, jamb of the east window.
Conclusions To prevent this alteration phenomenon from producing the use of adequate window filters (to retain the too strong radiations) is recommended. Knowing these types of alterations and taking the right decision to prevent them we avoid the formation and thus, the mechanical removal of metacinnabar as an integrant part of the original painting. Notes:
1. Paul Philippot, La notion de la patine et le nettoyage des peintures in Bulletin de l’Institut Royal du Patrimoine Arttistique, Bruxelles, IX, 1966, pp. 136-142.
2. Ioan Istudor, Alteration de la couleur observees sur les peintures murales des eglises de Bucovine, in Colloque sur la Conservation et la Restauration des Peintures Murales, Suceava, Romania, 1977, pp. 21- 35. 3. Rutherford J. Getens, Robert L. Feller and W. T. Chase, Vermillion and Cinnabar, in Studies in Conservation, 17 (1972), pp. 45-69. 4. The book of the art of Cennino Cennini: a contemporary practical treatise on quattrocento painting (1922), 15th century, George Allen & Unwin, London, Chapter 40. Of the properties of a red called cinnabar, and how it ought to be ground, free to download from: www.archive.org/details/bookofartofcenni00cennuoft 5. Dionysius of Furna, Carte de Pictură, Meridiane, Bucharest 1979, pp. 86, “Cartea întâi, îndreptar pentru meşteşug”, 66 paragraph. 6. Term used by Dionysius of Furna for the white pigment usually used in the Byzantine frescoes, prepared from grinded old intonaco. 7. The red pigment based on mercury sulphide was artificially prepared since the antiquity from sulphur and mercury. Starting with the 18th century (1785), it is commercialised under the name “vermillion”. 8. S. Savencu, A. Bordea, J. Linde, A. Luca, Chimie Analitică Calitativă, Ed. Didactică şi Pedagogică, Bucharest 1963, pp. 185 - 186 9. The chosen area to exemplify this process is located in the south apse, west window, west jamb, as the painting here is rich in cinnabar, applied on several decorative elements located at variable distances from the window. 10. Rutherford J. Getens et al., loc cit., pp. 54. *Note: Partial data presented in this article were previously published by Ioan Istudor and Geanina Roşu, in "Un fenomen de alterare al pigmentului roşu cinabru la Biserica Mănăstirii Suceviţa", Buletinul Centrului de Restaurare-Conservare, Iaşi, no 3/2004.
About the authors:
Ioan ISTUDOR
S.C. CERECS Art S.R.L., Bucharest Contact: bistudor@gmail.com Anca DINĂ
S.C. CERECS Art S.R.L.
Contact: anca@zappmobile.ro Geanina ROŞU
S.C. CERECS Art S.R.L.
Contact: geacorest@yahoo.com Doina Şeclăman Romanian National History Museum Contact: investita@mnir.ro Gheorghe NICULESCU National Research Institute for Conservation and Restoration, Bucharest Contact: niculescu.geo@gmail.com
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