POSTER AZE.PDF

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Reversion of blackened red lead-containing mural paintings by Reversion of blackened red lead-containing mural paintings by Laser irradiation: a preliminary study Laser irradiation: a preliminary study Sébastien Aze - Laboratoire du Centre Interrégional de Conservation et Restauration du Patrimoine (Marseille) Vincent Detalle, Nathalie Pingaud, Paulette Hugon - Laboratoire de Recherche des Monuments Historiques (Champs sur Marne) Natural ageing of red lead pigment (Pb 3 O 4 ) in mural paintings often lead to the formation of dark brown stains (Daniilia et al., 2000). due to the formation of plattnerite β-PbO 2 (Prasartset, 1996). The structure and the mechanisms of this alteration have been investigated through the analysis of naturally aged experimental wall paintings realised for the Laboratoire de Recherche des Monuments Historiques (LRMH) in 1977 (Aze, 2005). Raman micro-spectrometry analyses of darkened pictorial layers revealed the high sensitivity of β-PbO 2 to Laser irradiation. Excessive power cause the formation of inferior oxides (Pb 3 O 4 , PbO) through a series of oxygen losses, in accordance with thermal degrada- tion of β-PbO 2 (Burgio et al., 2001). In order to develop a specific restoration method of blackened red lead-containing paintings, the experimental conditions for the β-PbO 2 to Pb 3 O 4 reduction under Laser irradiation were investigated by Raman Micro-Spectrometry and X-ray Diffraction. Introduction Introduction Figure 2 : Raman spectra of pure plattnerite before (lower) and after irradiation (upper) with 785 nm diode laser (120 mW, 10 sec.) Figure 1: View of a plattne- rite pellet after irradiation with 785 nm diode Laser (G = 50x, P = 120 mW, t = 10 sec.) Experimental Experimental Preliminary investigations of the β-PbO 2 a Pb 3 O 4 transformation by Laser irradiation was carried out on pure plattnerite pellets in seve- ral conditions, including Laser power (P) and wavelength (λ), beam focalisation (G) and irradiation time (t). With 50x optical magnification and 785 nm diode Laser, the reaction was found to be complete with a 120 mW effective power irradiation during 10 seconds. The irradiation resulted in the formation of a 12 x 50 m reddish spot (fig. 1). Efficiency of the reaction was verified by subsequent Raman analyses of the irradiated area (fig. 2). A darkened red lead sample taken from the LRMH experimental wall painting was selected for the reversion experiments (fig. 3a). XRD analyses of the sample surface revealed the major presence of plattne- rite and few amounts of gypsum (fig. 3b). A 1,8 x 1,5 mm area was irra- diated with 785 nm Laser using a Renishaw InVia Raman system in the mapping mode with the following parameters: P=120 mW, G=50x, t=10 s, lateral step: 12 m (X), 50 m (Y). Figure 3 : (a) Surface of the darkened red lead paint sample after a 25 years ageing period. (b) X-Ray Diffractogram of the sample surface, showing the presence of plattnerite (P) and gypsum (G). After the irradiation, the reddish color (fig. 4a) is associated to the formation of Pb 3 O 4 , as attested by the Raman analyses of the sample surface (fig. 4b). Black areas are constituted by remaining plattnerite, due to the defocalization of the Laser beam on the relieves. Observation on the sample cross-section show that the rever- sion process has occurred only on the 15 m upper part of the alteration layer (fig. 4c). Figure 4 : (a) View of the sample surface after the reversion process (b) Raman spectrum obtained in a reddish area, revealing the presence of Pb 3 O 4 and few amounts of gypsum. (c) View of the stratigraphy of the paint sample after irradiation, showing the surficial reversion of β-PbO 2 into Pb 3 O 4 . References Aze S.: Altérations chromatiques des pigments au plomb dans les oeuvres du Patrimoine, thèse de doctorat de l’Université d’Aix-Marseille, 2005. Burgio L., Clark R. J. H., Firth S., Analyst 126 (2001), pp. 222-227. Daniilia S., Sotiropoulou S., Bikiaris D., Salpistis C., Karagiannis G., Chryssoulakis Y., Price B.E., Carlson J.H., Journal of Cultural Heritage 1 ( 2000), pp. 91-110. Prasartset C., in: Preprints of the 11th Triennial ICOM Committee for Conservation Meeting, Edimburgh, Scotland, 1 - 6 September 1996, Vol. 1, pp. 430-434. Conclusion Conclusion The conditions of the β-PbO 2 a Pb 3 O 4 transformation by Laser irradiation were accurately established for both 514 nm and 785 nm wavelengths. Irradiation of the plattnerite layer resulting from the alteration of red lead pigment led to a partial recovering of the initial color, as a result of the formation of a 15 m thick Pb 3 O 4 surficial layer. Consequently, additional essays might be carried out with longer irradiation times in order to obtain a complete rever- sion of the alteration layer.

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Reversion of blackened red lead-containing mural paintings by Reversion of blackened red lead-containing mural paintings by Laser irradiation: a preliminary study Laser irradiation: a preliminary study

Sébastien Aze - Laboratoire du Centre Interrégional de Conservation et Restauration du Patrimoine (Marseille)Vincent Detalle, Nathalie Pingaud, Paulette Hugon - Laboratoire de Recherche des Monuments Historiques (Champs sur Marne)

Natural ageing of red lead pigment (Pb3O4) in mural paintings often lead to the formation of dark brown stains(Daniilia et al., 2000). due to the formation of plattnerite β-PbO2 (Prasartset, 1996). The structure and the mechanismsof this alteration have been investigated through the analysis of naturally aged experimental wall paintings realised forthe Laboratoire de Recherche des Monuments Historiques (LRMH) in 1977 (Aze, 2005). Raman micro-spectrometryanalyses of darkened pictorial layers revealed the high sensitivity of β-PbO2 to Laser irradiation. Excessive power causethe formation of inferior oxides (Pb3O4, PbO) through a series of oxygen losses, in accordance with thermal degrada-tion of β-PbO2 (Burgio et al., 2001). In order to develop a specific restoration method of blackened red lead-containingpaintings, the experimental conditions for the β-PbO2 to Pb3O4 reduction under Laser irradiation were investigated byRaman Micro-Spectrometry and X-ray Diffraction.

IntroductionIntroduction

Figure 2: Raman spectra of pureplattnerite before (lower) andafter irradiation (upper) with 785nm diode laser (120 mW, 10sec.)

Figure 1: View of a plattne-rite pellet after irradiationwith 785 nm diode Laser (G= 50x, P = 120 mW, t = 10sec.)

ExperimentalExperimental

Preliminary investigations of the β-PbO2a Pb3O4 transformationby Laser irradiation was carried out on pure plattnerite pellets in seve-ral conditions, including Laser power (P) and wavelength (λ), beamfocalisation (G) and irradiation time (t). With 50x optical magnificationand 785 nm diode Laser, the reaction was found to be complete with a120 mW effective power irradiation during 10 seconds. The irradiationresulted in the formation of a 12 x 50 µm reddish spot (fig. 1).Efficiency of the reaction was verified by subsequent Raman analysesof the irradiated area (fig. 2).

A darkened red lead sample taken from the LRMH experimentalwall painting was selected for the reversion experiments (fig. 3a). XRDanalyses of the sample surface revealed the major presence of plattne-rite and few amounts of gypsum (fig. 3b). A 1,8 x 1,5 mm area was irra-diated with 785 nm Laser using a Renishaw InVia Raman system in the�mapping mode� with the following parameters: P=120 mW, G=50x,t=10 s, lateral step: 12 µm (X), 50 µm (Y).

Figure 3: (a) Surface of the darkened red lead paint sample aftera 25 years ageing period. (b) X-Ray Diffractogram of the samplesurface, showing the presence of plattnerite (P) and gypsum (G).

After the irradiation, the reddish color (fig.4a) is associated to the formation of Pb3O4, asattested by the Raman analyses of the samplesurface (fig. 4b). Black areas are constituted byremaining plattnerite, due to the defocalizationof the Laser beam on the relieves. Observationon the sample cross-section show that the rever-sion process has occurred only on the 15 µmupper part of the alteration layer (fig. 4c).

Figure 4: (a) View of the sample surface after the reversion process (b) Raman spectrum obtainedin a reddish area, revealing the presence of Pb3O4 and few amounts of gypsum. (c) View of thestratigraphy of the paint sample after irradiation, showing the surficial reversion of β-PbO2 intoPb3O4.

ReferencesAze S.: Altérations chromatiques des pigments au plomb dans les oeuvres du Patrimoine, thèse de doctorat de l’Université d’Aix-Marseille, 2005.Burgio L., Clark R. J. H., Firth S., Analyst 126 (2001), pp. 222-227.Daniilia S., Sotiropoulou S., Bikiaris D., Salpistis C., Karagiannis G., Chryssoulakis Y., Price B.E., Carlson J.H., Journal of Cultural Heritage 1 ( 2000), pp. 91-110.Prasartset C., in: Preprints of the 11th Triennial ICOM Committee for Conservation Meeting, Edimburgh, Scotland, 1 - 6 September 1996, Vol. 1, pp. 430-434.

ConclusionConclusion

The conditions of the β-PbO2 a Pb3O4 transformation by Laser irradiation were accurately established for both514 nm and 785 nm wavelengths. Irradiation of the plattnerite layer resulting from the alteration of red lead pigmentled to a partial recovering of the initial color, as a result of the formation of a 15 µm thick Pb3O4 surficial layer.Consequently, additional essays might be carried out with longer irradiation times in order to obtain a complete rever-sion of the alteration layer.