Framework

The Alcobaça Monastery, classified by UNESCO as World Heritage since 1987, possesses a wide and valuable collection of terracotta sculptures from 17th century made by Cister’s monks. These sculptures have large proportions, with more than 2 metres high, composed by pieces of 40 to 50 cm high namely “tacelos”.

They present a bad conservation state that calls for an urgent intervention. Studies carried out by a team member [1-3] showed the importance of these sculptures, especially in an historic and artistic context. These studies must be deepened in such fields like iconography and production and must address the diffusion of the Alcobaça clay sculpture. The activity behind these works show important developments since the 17th century and since then Alcobaça was considered an important production and export ceramic centre [4, 5]. Also the polychromy studies will allow contextualising the dress habits and the type of tissues used in those times, mainly by the kings, court and clergy. Since the end of XIX century, several studies with terracotta have been published [6]. Although, only a few papers are about compositional characterization and/or cleaning conservation proceeds. Therefore, not much is known of the materials and techniques used for the sculptures production, at least in Portugal [7]. It is our intension to develop studies leading either to a better knowledge of the terracotta support and polychromy layers characterization, and also their degradation processes, to sustain the main aim which is the investigation and development of products and solutions as consolidants based in geopolymers composites made with metakaolinite [8, 9] with specific properties to mitigate the hard degradation process showed by the sculptures.

There are some published studies about terracotta sculptures that support the methodology proposed to for this effort [10, 11]. Therefore other important works related with the identification of crystalline phases after firing, and ceramic technological properties like firing retraction, water absorption and mechanical bending strength were considered [12, 13]. From the information obtained, namely the chemical data, studies will be done through multivariate statistical analysis that can allow the determination of similarities, and so the raw material provenance, between samples taken from sculptures and clay samples from the surround region, as we can observe in a large international bibliography [14, 15]. Some team members already did this type of studies [16, 17].

Polychromy, gilding leaf and binder media layers studies were of special interests to improve the state of art of the pigments and techniques used in 17th century, in order to complement studies already made by researchers of this team [18-20]. It is also important to compare with the few data available, about the woodcraft sculpture and canvas painting polychromies [21] that show, the use of simple stratigraphy and a small number of pigments. Therefore, it is not already made the comparison between the materials and techniques used in color layers on terracotta sculptures with similar motifs as the sculptures in wood or in paintings from the same epoch, in order to determine any particular specificity. In other words, the relationship in terms of materials and techniques of painting of ceramic sculptures and other forms of painting art could be clarified. The “in situ” analysis with energy dispersive X-ray fluorescence spectrometry (EDXRF) technique will be used to the pigment identification as some authors already done [22, 23]. Microsamples will be encapsulated in a resin and they will be analyzed by other techniques, some of them in first hand, to complement the study about the pigments and binders used and allow the comparison with the materials and techniques traditionally used in others art works at the epoch. As other studies about pigments and binder media in terracotta sculptures were carried out by other teams on several analytical techniques, both non-intrusive used in situ and on microsampes analysed in a laboratory context [24, 25].

Technologic studies will be done with clays that show similarities with terracotta sculptures after plastic conformation and firing at several temperatures using techniques applied by team elements in other related studies. These technologic studies will allow the characterization of the technology involved in the sculptures production, such as conformation phases and firing temperature, amongst others aspects, as already done by some members of the team [26]. The proofs will also be used in accelerated aging tests aiming the construction of a conceptual model of the materials alteration, as done by others. .The geopolymeric composites are a new kind of materials that are being investigated in several areas [27] and members of the team have work in some of them [28, 29]. In 1978, Davidovits [30] proposed that binders could be produced by a polymeric reaction of alkaline liquids with the silicon and the aluminium in source materials of geological origin or by-product materials such as fly ash and rice husk ash. To that reaction he called geopolymerization and under gone by reactive aluminossilicates (eg. metakaoline) in highly alkaline media, resulting in the precipitation of zeolite-like poorly-crystalline or amorphous alkali aluminossilicates, with high-strength and stable properties. Theoretically, all aluminossilicate materials can be alkali activated, however, raw materials should have, in order to make alkali cement with them, some conditions such as the material solubility in basic media should be high and the availability of Al₂ O₃ and SiO₂ in the environment should also be high [30]. The main binder produced is a C-S-H gel, as the result of the hydration process and with general properties that allow interesting perspectives to be used in the terracotta sculptures conservation, and restoration, as consolidants and binders.

Many conservation treatments as polyvinyl alcohol, Portland cement, ethyl silicate, epoxy and acrylics resins have been applied to earthen structures with limited success and the compatibility of this kind of materials was already tested with success in the reinforcement of the terracotta sculptures [8].

Finally, the conservation and restoration intervention will be done with the ethical criteria oriented by the guidelines of the European Confederation of Conservator-Restorers' Organisations (E.C.C.O.).

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2. Moura, Carlos, “Da figuração à decoração. O percurso artístico dos mosteiros cistercienses em Portugal entre os séculos XVI e XVIII”, Arte de Cister em Portugal e Galiza, Arte del Císter en Galicia y Portugal, Fundação Calouste Gulbenkian, Fundação Pedro Barrié de La Maza, Lisboa, 1998, p. 329-375.
3. Moura, Carlos, A Escultura de Alcobaça e a Imaginária Monástico-Conventual (1590-1700), Dissertação de Doutoramento, Universidade Nova de Lisboa/Faculdade Ciências Sociais e Humanas, Lisboa, 2006, 2 vols.
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