Study of the degradation causes affecting stucco sculptures from the Valentino Castle in Turin

Abstract17th century stuccos located in The Valentino Castle in Turin (Northern Italy) have been studied by means of XRD, TG-DTA, Hg porosimetry and SEM coupled with EDX chemical analysis in order to understand their composition and the degradation causes. The investigated un-degraded samples were made of gypsum, hydrated lime and other carbonates phases on the external surface and up to ca. 20 mm in depth but the compositions were highly heterogeneous. Repeated cycles of water impregnation, coming from roofing infiltration, and evaporation have reached the investigated area and led to severe damages to stuccos due to crystallization of hydrated magnesium sulphate salts.RésuméDes stucs du XVIIe siècle sintués dans le Château du Valentino (Turin, Italie) ont été analysés par diffraction des rayons X. ATG/ATD, porosimétrie à mercure et microscopie électronique à balayage avec microanalyse EDX, pour en étudier la composition et les causes qui ont conduit à leur endommagement. L'étude des décorations intactes a montré que celles-ci ont été réalisée à base de liants aériens en surface et jusqu'à une profondeur de 20 mm, mais les compositions de différents échantillons ne sont pas du tout homogènes. Des cycles successifs d'imprégnations et d'évaporation d'eau, suite à des infiltrations répétées provenant du toit, ont sévèrement dégradé les décoration à cause de la cristallisation de sels de sulfate de magnésium.

[1]  J. Sharp,et al.  The bed-depth effect in the thermal decomposition of carbonates , 1993 .

[2]  S. Warne,et al.  Potential for coal calorific value corrections, dependent on the carbonate mineral type present , 1988 .

[3]  H. Huhn.  High-temperature synthesis of magnesium silicates from solid mixtures of SiO2 and various magnesium compounds , 1988 .

[4]  R. C. Mackenzie,et al.  The thermal dissociation of some carbonate minerals , 1971 .

[5]  J. Dubrawski.  Thermal decomposition of some siderite-magnesite minerals using DSC , 1991 .

[6]  Cristobal Viedma,et al.  Salt crystallization in porous construction materials I Estimation of crystallization pressure , 1997 .

[7]  S. Warne,et al.  Use of differential scanning calorimetry in measuring the thermal decomposition of mineral carbonates occurring in coal , 1987 .

[8]  N. B. Singh,et al.  Hydration of hemihydrate of gypsum and its supersaturation , 1978 .

[9]  R. Naumann,et al.  Thermal decomposition of the magnesium sulphate hydrates under quasi-isothermal and quasi-isobaric conditions , 1990 .

[10]  A. Searcy,et al.  Kinetics and Thermodynamics of Decomposition of Dolomite to a Metastable Solid Product , 1978 .

[11]  J. Sharp,et al.  The effect of procedural variables on TG, DTG and DTA curves of magnesite and dolomite , 1991 .

[12]  L. Odochian.  Study of the nature of the crystallization water in some magnesium hydrates by thermal methods , 1995 .

[13]  A. Fazeli,et al.  Thermal decomposition of rhombohedral double carbonates of dolomite type , 1991 .

[14]  Giuseppe Montana,et al.  The “recipe” of the stucco sculptures of Giacomo Serpotta , 2002 .

[15]  W. Smykatz-kloss,et al.  Thermal Characterization of Dolomites , 2001 .