Síntese e caracterização de pigmentos amarelos de crómio segundo fontes históricas

Acabou de ser disponibilizada livremente a seguinte tese de mestrado:

Vanessa Otero Matias, Historically accurate reconstructions and characterisation of chrome yellow pigments, Lisboa, Faculdade de Ciências e Tecnologia da Universidade Nova de Lisboa, 2010.

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Resumo:

A detailed knowledge of the materials used by artists is essential to unveil their techniques and to place their works in context as well as to establish the most adequate conservation and authentication procedures. Such knowledge arises from reliable documentary sources of technical information contemporary to artists and the preparation of historically accurate reconstructions. Deciphering the words of the past to unravel art technology is far from straightforward, representing one of the most challenging issues within the art conservation field. Chrome yellow pigment belongs to the 19th century artists’ palette. It was enthusiastically used by many artists even when its use was deemed inadvisable. The Portuguese modern painter, Amadeo de Souza-Cardoso, was one of these artists known to have used it. The aim of this work was the manufacture of chrome yellow pigments with as much historical accuracy as possible. This was the first time the Winsor & Newton 19th Century Artists’ Materials Database was systematically explored to support pigment manufacture. The recipes taken from this database were broken down into their relevant steps. This study proposes a correct correspondence between original materials and their current equivalent. A total of 34 pigments and 3 minerals were characterised by EDXRF, Raman, FTIR, XRD and SEM-EDS. Regardless of the recipe or process variations, lead chromate was identified in the majority of the pigments. Depending on the pH, other compounds were also detected. Basic lead chromate was obtained under alkaline conditions, giving rise to an orange hue. Mixed-crystals of lead chromate and lead sulphate were formed under acidic conditions, presenting a lemon hue. All the extenders used, namely calcite, barytes and gypsum, were detected. Notably, cerussite and calcite were also identified even though they were not added as such during the pigment manufacture. Moreover, a comparison with case studies samples was performed. Pure lead chromate and mixed-crystals of lead chromate and lead sulphate were identified in the presence of calcite, barytes and cerussite. Proposals concerning the formulation of these pigments are suggested. A multi-analytical approach proved to be fundamental for the characterisation of all the pigments.