Characterization of painting materials in a South American polychromy

B. GOMEZ; S. PARERA; MARTA MAIER; GABRIELA SIRACUSANO

Cancun

Congreso; Congreso.XVIII International Materials Research Congress 2009 - 2º Simposio Latinoamericano sobre Métodos Físicos y Químicos en Arqueología, Arte y Conservación del patrimonio Cultural (LASMAC 2009); 2009

MATERIALS RESEARCH SOCIETY-LASMAC

South American polychrome sculptures produced during the so-called Colonial period (S.XVII-XVIII) are part of what has been identified as the process of evangelization done under the Spanish domain. These images, installed in churches, convents or small chapels, show the diverse iconographic discourses that were necessary to develop that process: virgins, saints, christs, etc., manufactured in workshops by Spanish, indigenous and creoles people, who used diverse materials ?wood, stone, etc- to carve and paint them. The identification of pigments, dyes, resins, clays or gold by chemical analysis is relevant, as those results can be contrasted with past manuscripts and prints (inventories, merchandise lists, manuals, treatises) where those materials are described or mentioned by their uses and meanings in that region. In this study, we have worked on a stone sculpture of the Immaculate Conception produced in a Jesuit Mission of Paraguay during the XVIII century. Several analytical techniques were used to identify pigments, the plaster layer and binding media. First, cross sections of five samples were examined by optical microscopy and SEM-EDX. Then, application of transmitted FT-IR spectroscopy confirmed the presence of gypsum, Ca2SO4.2H2O, as the plaster. Green earth, minium, Prussian blue and Naples yellow were identified by SEM-EDX, FT-IR and microchemical tests. Analysis of binding media by staining tests on cross sections of the samples and FT-IR spectroscopy revealed the presence of lipids. Further analysis of a selected sample by gas chromatography and gas chromatography coupled to mass spectrometry showed the presence of lauric acid as the principal fatty acid, together with minor amounts of capric, caprylic, myristic, palmitic, and stearic acids, characteristic of coconut oil.