Thermal properties and stability of Catalan Modernist blue and green enamels

Abstract

Stained glass is a fragile component of our Cultural Heritage. In particular, the stained glass produced during the last decades of the 19th century and first decades of the 20th century is characterised by the use of a new type ready-to-use enamels. Stained glass was used for the windows of buildings, and a large part of it is exposed to weathering and consequently to deterioration. This study analyses the collection of materials used in one of the most important stained glass Modernist workshops in Barcelona. The chemical composition is determined (and pigments identified) by means of Laser Ablation Inductively-Coupled Plasma Mass Spectrometry and X-Ray Diffraction and the thermal properties of the enamels measured by Differential Scanning Calorimetry and Hot Stage Microscopy. The enamels are made of a lead-zinc borosilicate glass characterised by its low sintering temperatures and high stability against chemical corrosion, in particular to water corrosion. However, the relatively narrow range of firing temperatures necessary for correct adherence of the enamels to the contemporary glass base may have required the addition of a high lead borosilicate flux, which would have increased the lead content of the enamel, decreasing the firing temperature but also its stability. K E Y W O R D Schemical stability, lead borosilicate glass, Modernist enamels, softening temperature

Impact of solar radiation and environmental temperature on Art Nouveau glass windows

“…The different surface temperature observed on the paint and the support glass could promote the thermal incompatibility in the Atelier panel, mainly on bluish and purplish enamels, favoring the formation of fissures and the mass loss [59].…”

Modernist enamels: Composition, microstructure and stability

“…glass transition, deformation and softening temperatures) were determined. Our study [12] demonstrated that the enamels were "ready-for-use" and had been manufactured by various companies from all over Europe, even though the mixture of enamels and the modification of their composition can also be expected.…”

“…The use of smalt, a high lead-potash cobalt glass, in the blue enamels has been given as one of the main reasons for their discolouration; discolouration of smalt is due to the leaching of K + in a humid environment which results in the change of the cobalt ions from blue tetrahedral to pink octahedral coordination [10]. However, our studies have shown that smalt was not used in the Modernist Catalan enamelled glass [12], probably because the discolouration of smalt was already well known by then.…”

“…In order to assess the role of the composition of the enamels and base glasses and the firing temperature in the degradation of the blue and green enamels applied over stained glasses from the Catalan Modernist workshops, we conducted a multitechnique investigation of the enamels used by Rigalt, Granell & Cia., one of the most important Modernists workshops in Barcelona [12]. The company was founded in 1890 by Antoni Rigalt i Blanch (1850-1914) and Jeroni F. Granell i Manresa (1868-1923), later Granell & cia (1923Granell & cia ( -1931 [2].…”

“…The blue and green enamels were made of a lead-zinc borosilicate glass (30-40 % PbO, 0-15 % ZnO, 15-19 % B 2 O 3 ) with softening temperatures varying between 583 o C and 617 o C, mixed with colourants or pigment particles [12]. These compositions are characterised by their low sintering temperatures and a reasonable stability against water corrosion [13].…”