Decorative 18th Century Blue-and-White Portuguese Tile Panels: A Type-Case of Environmental Degradation

Teresa P Silva,Maria-Alexandra Barreiros,Maria-Ondina Figueiredo,Maria-Isabel Prudêncio

doi:10.1155/2013/972018

Teresa P Silva, Maria-Alexandra Barreiros + Show 2 more

Open Access

https://doi.org/10.1155/2013/972018

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Abstract

Decorated glazed ceramic tiles are used as an ornamental art, constituting an important cultural heritage whose preservation is mandatory. Environmental conditions are responsible for the degradation of exposed ancient tile panels originating various pathologies, related to the development of microorganisms. This is the case of a valuable 18th century blue-and-white Portuguese tile panel called “Cura do Cego,” belonging to the collection of the National Tile Museum (MNAz), where green stains are nowadays observable in the glaze. A prospective diagnosis of this green tarnishing was the aim of the present work. Small tile fragments were directly irradiated using nondestructive techniques: X-ray fluorescence spectrometry with a wavelength-dispersive system (WDXRF) for chemical characterization of the tile glaze and X-ray powder diffraction (XRD) to assess the phase constitution of both the glaze and the ceramic body. A destructive technique (scanning electron microscopy with energy-dispersive system (SEM/EDS)) was applied to tentatively infer the chemical changes induced in the glaze by the green staining and also to characterize the morphology of the microorganisms associated to this staining. The obtained results are reported and discussed, as a preliminary step for testing an innovative nondestructive decontamination technique applying gamma radiation, particularly suitable for overcoming such tile pathologies.

Highlights

The original location of the panel “Cura do Cego” (Figure 1) is yet unknown; the importance attributed to this panel has motivated a previous consolidation and restoration treatment performed at MNAz, along with a prospective diagnosis of the nowadays observed green stains which is described in the present work
The low temperature form of silica is possibly present, denoting the ageing of the glaze—a degradation process that starts with a partial devitrification of the siliceous glassy matrix [3]
The contents of oxygen, silicon, and lead are high in the glaze; on the other hand, the strong emission line of carbon and the vestigial occurrence of nitrogen in the small aggregate lodged at the altered glaze surface conform to the presence of microorganisms

Summary

Introduction

“Azulejos”—Portuguese word designating glazed ceramic tiles—have been widely used along the last five centuries, covering the interior or placed in the exterior (facades) of churches, monasteries, and palaces, and have been progressively applied in other constructions like particular houses and underground stations [1] linking aesthetic qualities to utilitarian and practical functions This valuable cultural heritage deserves nowadays particular attention due to the serious degradation presented by some decorative tile panels, a concern that has pushed the Portuguese National Tile Museum in Lisbon (Museu Nacional do Azulejo (MNAz)) to promote the training of specialized personnel in conservation and restoration in the last decades with the purpose of desirably eliminating the agents responsible for the deterioration of ancient tiles [2]. The present study is a preliminary step towards future tile conservation actions involving the use of gamma radiation, along with neutron beams [13], with the purpose of getting rid of microorganisms without damaging that valuable cultural object

Brief History of the Studied Tile Panel ‘‘Cura do Cego’’

Materials and Methods

Results and Discussion

Background

Final Comments

Conflict of Interests