title: Ochres and earths: matrix and chromophores characterization of 19th and 20th century artist materials.
abstract: The present paper describes the main results obtained from the characterization of a wide range of natural and synthetic ochre samples used in Portugal from the 19th to the 20th century, including powder and oil painting samples. The powder ochre samples came from several commercial distributors and from the collection of Joaquim Rodrigo (1912-1997), a leading Portuguese artist, particularly active during the sixties and seventies. The micro-samples of oil painting tubes came from the Museu Nacional de Arte Contemporânea-Museu do Chiado (National Museum of Contemporary Art-Chiado Museum) in Lisbon and were used by Columbano Bordalo Pinheiro (1857-1929), one of the most prominent naturalist Portuguese painters. These tubes were produced by the main 19th century colourmen: Winsor & Newton, Morin et Janet, Maison Merlin, and Lefranc. The samples have been studied using μ-Fourier Transform Infrared Spectroscopy (μ-FTIR), Raman microscopy, μ-Energy Dispersive X-ray fluorescence (μ-EDXRF), and X-ray diffraction (XRD). The analyzed ochres were found to be a mixture of several components: iron oxides and hydroxides in matrixes with kaolinite, gypsum and chalk. The results obtained allowed to identify and characterize the ochres according to their matrix and chromophores. The main chromophores where identified by Raman microscopy as being hematite, goethite and magnetite. The infrared analysis of the ochre samples allowed to divide them into groups, according to the composition of the matrix. It was possible to separate ochres containing kaolinite matrix and/or sulfate matrix from ochres where only iron oxides and/or hydroxides were detected. μ-EDXRF and Raman were the best techniques to identify umber, since the presence of elements such as manganese is characteristic of these pigments. μ-EDXRF also revealed the presence of significant amounts of arsenic in all Sienna tube paints.
authors.affiliation: Department of Conservation and Restauration, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, Campus Caparica, 2829-516 Caparica, Portugal.
authors.forename: Cristina
authors.initials: C
authors.lastname: Montagner
authors.forename: Diogo
authors.initials: D
authors.lastname: Sanches
authors.forename: Joana
authors.initials: J
authors.lastname: Pedroso
authors.forename: Maria João
authors.initials: MJ
authors.lastname: Melo
authors.forename: Márcia
authors.initials: M
authors.lastname: Vilarigues
mesh_terms: D004396:Coloring Agents / Q000032:analysis* / Q000266:history*; D049672:History, 19th Century; D049673:History, 20th Century; D008853:Microscopy; D010150:Paint / Q000032:analysis* / Q000266:history*; D010151:Paintings / Q000266:history*; D011174:Portugal; D013052:Spectrometry, X-Ray Emission; D017550:Spectroscopy, Fourier Transform Infrared; D014961:X-Ray Diffraction
chemical_list: D004396:Coloring Agents