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An investigation on the suitability and stability of a new pigmented wax-resin infill formulation to be used in the conservation of paintings
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Orientador(es)
Resumo(s)
As formulações de cero-resina pigmentadas (CRP) têm vindo a ser utilizadas
para preencher e reintegrar lacunas em pinturas e outros objetos pelo menos desde o
século XVIII. Estas formulações consistem em misturas de uma cera e de uma resina,
às quais são adicionados uma carga/material inerte (como o carbonato de cálcio) e/ou
pigmentos. A possibilidade de adicionar pigmentos diretamente à mistura é uma das
maiores vantagens deste material, uma vez que permite que o preenchimento e a rein-
tegração cromática sejam, potencialmente e quando a pintura o permite, realizados
numa única etapa. Por outro lado, os preenchimentos com CRP podem receber textu-
ras (através, por exemplo, de moldes de silicone) e ser esculpidos (por exemplo, para
recriar pinceladas ou outras características topográficas da superfície), para além de
serem facilmente removíveis mecanicamente ou com solventes de baixo índice aromá-
tico.
Um dos materiais comummente utilizado nas formulações tradicionais de cero-
resina e, mais recentemente, presente nas formulações produzidas comercialmente
pela Gamblin Conservation Colors, é a cera de abelha. A cera de abelha tem, no entanto,
evidenciado desenvolver bloom (uma fina camada esbranquiçada que surge na super-
fície e altera a sua aparência e legibilidade), bem como corroer os suportes metálicos
por vezes utilizados em pinturas a óleo.
Encontrar um material adequado para substituir a cera de abelha que pudesse
ser combinado com uma resina sintética estável, tornou-se o foco de estudos recentes
realizados na Faculdade de Ciências e Tecnologia da Universidade Nova de Lisboa
(Lisboa, Portugal). Os resultados mais promissores foram alcançados com dois materiais sintéticos: a cera microcristalina Cosmoloid H80 e a resina hidrocarbonada
hidrogenada Regalrez® 1126. O principal objetivo do presente projeto de investigação
consistiu em confirmar a adequabilidade destes materiais na composição de uma for-
mulação de CRP inerte e estável, com boas propriedades físicas, visuais e de manuse-
amento.
A primeira parte da investigação centrou-se em compreender qual a influência
dos materiais (Cosmoloid H80, Regalrez® 1126, cargas e pigmentos), e da sua presença
em diferentes proporções, nas propriedades físicas e visuais das formulações, e ainda
no seu comportamento em termos de preparação e aplicação.
A segunda parte consistiu na avaliação da estabilidade das formulações das
CRP em estudo a flutuações de temperatura e humidade relativa, uma vez que estas
podem influenciar o desenvolvimento de bloom, e porque as ceras são, em geral, sen-
síveis à temperatura. Os resultados foram avaliados através de fotografia macro, mi-
croscopia digital, medições de dureza, e Espectroscopia no Infravermelho por Trans-
formada de Fourier no modo de Reflexão Total Atenuada (FTIR-ATR), e foram com-
parados com os obtidos para as formulações de CRP produzidas pela Gamblin Conser-
vation Colors. Por último, foi testada uma pequena gama de vernizes e materiais de
reintegração cromática para verificar a respetiva compatibilidade com as formulações
de CRP.
A terceira e última parte da investigação procurou compreender de forma mais
realista como é que as formulações CRP podem ser aplicadas em diferentes situações.
Para tal, foram utilizadas, como casos de estudo, duas pinturas pertencentes ao
Stichting Restauratie Atelier Limburg (Maastricht, Países Baixos).
Os resultados mostraram que as formulações de CRP não desenvolvem bloom
quando sujeitas a flutuações de humidade relativa e/ou temperatura. Para além disso,
quando expostas a temperaturas até 60º C, não apresentam alterações significativas
ou amolecimento visível, mantendo qualquer textura previamente aplicada.
As formulações CRP provaram ser particularmente úteis nos casos em que é
necessário reconstruir em detalhe uma textura/pincelada ou quando estão em causa
áreas monocromáticas em que, simultaneamente ao preenchimento da lacuna, é pos-
sível fazer uma reintegração de cor precisa. Tendo-se comprovado a compatibilidade
das CRP em estudo com alguns dos vernizes e materiais de reintegração cromática
mais comuns, verificou-se que estes materiais podem também ser reintegrados cro-
maticamente e/ou ser ajustados com velaturas de cor mais ou menos transparentes.
Pigmented wax-resin (PWR) formulations have been used to infill and reinte- grate losses in paintings and other objects at least since the 18th century. These formu- lations consist of mixtures of a wax and a resin, to which an inert material (such as chalk) and/or pigments are added. The possibility of adding pigments directly to the mixture is a significant advantage for it enables infilling and colour reintegration to be done in a single step. PWR infills can also receive texture and be sculpted (e.g., to recreate brushstrokes or other topographical features) and are easily removable me- chanically or with low-aromatic solvents. One of the most common materials present in traditional PWR formulations, produced either by conservators themselves or, more recently, by Gamblin Conserva- tion Colors, is beeswax. Beeswax has, however, been reported to develop bloom (a thin whitish layer on the surface) and to corrode metal supports where used in oil painting. Finding an appropriate replacement material for beeswax which could be com- bined with a stable synthetic resin, became the core of recent studies conducted at the NOVA School of Science and Technology (Lisbon, Portugal). The most promising re- sults were achieved with two synthetic materials: Cosmoloid H80 microcrystalline wax and Regalrez® 1126 hydrogenated hydrocarbon resin. Establishing the best for- mulations and confirming their suitability as an inert and stable infill material, with good physical, optical and handling properties, was the aim of this research project. The first part focusses on understanding how the materials (Cosmoloid H80, RegalrezÒ 1126, inert fillers and pigments) and their presence in different proportions influences not only the physical and visual properties of the formulations, but also their behaviour in terms of preparation and application. The second part entails an evaluation of the stability of the NOVA-PWR for- mulations (PWR developed at NOVA, containing Cosmoloid H80, RegalrezÒ 1126, in- ert fillers and pigments) to fluctuating temperature and relative humidity, because these are considered possible factors in the development of bloom, and because waxes are, in general, temperature sensitive. Results were assessed with macro photography, digital microscopy, hardness measurements and ATR-FTIR spectroscopy, and were compared to those obtained for Gamblin Pigmented Wax/Resin formulations. Finally, a small range of varnishes and inpainting materials was tested for its compatibility with the PWR formulations. The third and final part of the research aims at understanding realistically how the PWR formulations can be applied in different situations. For that purpose, two paintings belonging to the Stichting Restauratie Atelier Limburg (Maastricht, The Neth- erlands) were used as case studies. Results showed that the NOVA-PWR formulations do not develop bloom when subjected to fluctuations in relative humidity and/or temperature. In addition, they do not exhibit any significant changes or softening when exposed to tempera- tures as high as 60º C, maintaining any texture previously applied. PWR formulations proved to be particularly useful where a detailed reconstruction of tex- ture/brushstrokes was required or in monochromatic areas where an accurate colour match can be achieved at the same time as infilling the loss. Found to be compatible with some of the most common varnishes and inpainting materials, NOVA-PWR in- fills can also receive inpainting or be adjusted with coloured glazes.
Pigmented wax-resin (PWR) formulations have been used to infill and reinte- grate losses in paintings and other objects at least since the 18th century. These formu- lations consist of mixtures of a wax and a resin, to which an inert material (such as chalk) and/or pigments are added. The possibility of adding pigments directly to the mixture is a significant advantage for it enables infilling and colour reintegration to be done in a single step. PWR infills can also receive texture and be sculpted (e.g., to recreate brushstrokes or other topographical features) and are easily removable me- chanically or with low-aromatic solvents. One of the most common materials present in traditional PWR formulations, produced either by conservators themselves or, more recently, by Gamblin Conserva- tion Colors, is beeswax. Beeswax has, however, been reported to develop bloom (a thin whitish layer on the surface) and to corrode metal supports where used in oil painting. Finding an appropriate replacement material for beeswax which could be com- bined with a stable synthetic resin, became the core of recent studies conducted at the NOVA School of Science and Technology (Lisbon, Portugal). The most promising re- sults were achieved with two synthetic materials: Cosmoloid H80 microcrystalline wax and Regalrez® 1126 hydrogenated hydrocarbon resin. Establishing the best for- mulations and confirming their suitability as an inert and stable infill material, with good physical, optical and handling properties, was the aim of this research project. The first part focusses on understanding how the materials (Cosmoloid H80, RegalrezÒ 1126, inert fillers and pigments) and their presence in different proportions influences not only the physical and visual properties of the formulations, but also their behaviour in terms of preparation and application. The second part entails an evaluation of the stability of the NOVA-PWR for- mulations (PWR developed at NOVA, containing Cosmoloid H80, RegalrezÒ 1126, in- ert fillers and pigments) to fluctuating temperature and relative humidity, because these are considered possible factors in the development of bloom, and because waxes are, in general, temperature sensitive. Results were assessed with macro photography, digital microscopy, hardness measurements and ATR-FTIR spectroscopy, and were compared to those obtained for Gamblin Pigmented Wax/Resin formulations. Finally, a small range of varnishes and inpainting materials was tested for its compatibility with the PWR formulations. The third and final part of the research aims at understanding realistically how the PWR formulations can be applied in different situations. For that purpose, two paintings belonging to the Stichting Restauratie Atelier Limburg (Maastricht, The Neth- erlands) were used as case studies. Results showed that the NOVA-PWR formulations do not develop bloom when subjected to fluctuations in relative humidity and/or temperature. In addition, they do not exhibit any significant changes or softening when exposed to tempera- tures as high as 60º C, maintaining any texture previously applied. PWR formulations proved to be particularly useful where a detailed reconstruction of tex- ture/brushstrokes was required or in monochromatic areas where an accurate colour match can be achieved at the same time as infilling the loss. Found to be compatible with some of the most common varnishes and inpainting materials, NOVA-PWR in- fills can also receive inpainting or be adjusted with coloured glazes.
Descrição
Palavras-chave
Pigmented wax-resin Cosmoloid H80 Regalrez® 1126 infilling reintegration suitability