Colorimetric Evaluation of Pictorial Coatings in Conservation of Plasterworks from the Islamic Tradition
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Collado Montero, Francisco José; Calero Castillo, Ana Isabel; Melgosa Latorre, Manuel; Medina Flórez, Víctor J.Editorial
Routledge, Taylor & Francis Group
Materia
Plasterwork Islamic heritage Colour coating
Date
2019Referencia bibliográfica
Collado-Montero, Francisco José, Calero-Castillo, Ana Isabel, Melgosa, Manuel and Medina, Víctor Jesús (2019). Colorimetric evaluation of pictorial coatings in conservation of plasterworks from the Islamic tradition. Studies in Conservation, 64(2), 90-100. DOI: 10.1080/00393630.2018.1460924.
Sponsorship
Ministerio de Economía y Competitividad (Gobierno de España), with support from European Regional Development Fund (ERDF), within the framework of Research Projects HAR2015-66139-P and FIS2016-80983-P; Consejería de Economía, Innovación, Ciencia y Empleo, Junta de Andalucía (Research Project P12-HUM-1941).Abstract
The main aim of our current investigation is the colorimetric evaluation of protective treatments
(consolidants) applied to traditional Islamic plasterworks, under natural ageing conditions. From
analyses of the original pictorial plaster remains in the Courtyard of the Maidens of the Real
Alcázar in Seville, Spain (a World Heritage Site) we prepared test specimens, using materials
and techniques similar to the original ones. We analysed 56 test specimens painted with four
pigments (yellow, green, blue, and red), using two different binders (animal glue and gum
arabic), onto which five representative consolidants were applied: barium hydroxide, acrylic
copolymer, polyvinyl butyral, ethyl silicate, and bacterial carbonatogenesis. The test
specimens were subjected to natural ageing for one year (indoors and outdoors), enabling a
colorimetric assessment to be made of the changes of the polychrome surfaces. The
colorimetric heterogeneity of the 56 specimens after ageing registered an average value of
2.7 CIELAB units, assessed using the mean colour difference with respect to the mean. In the
aged specimens, the addition of consolidants resulted in average colour differences (mainly
lightness differences) of 10.7 and 6.7 CIELAB units, considering as a reference the specimens
without consolidants aged indoors and outdoors, respectively. These colour differences were
very similar for both binders but not for the four pigments, higher values being found for
the blue and red pigments. Considering as reference the samples without consolidants aged
outdoors, we found no statistically significant colour differences, either among the five
consolidants (p = .094) nor the two binders (p = .674) used. In addition to the magnitude of
colour differences, the choice of the most appropriate consolidants must also consider
aspects related to performance and effectiveness. Overall, for the type of paints tested, the
polyvinyl butyral consolidant appeared to perform the best, followed by the ethyl silicate.