title: A definitive analytical spectroscopic study of Indian yellow, an ancient pigment used for dating purposes.
abstract: The Raman spectrum of tartrazine has been mistakenly reported as being that of Indian yellow in the literature, which has serious consequences for the identification of this pigment in art works regarding their authentication. Unlike tartrazine, Indian yellow (a natural mixture of the magnesium and calcium salts of euxanthic acid) exhibits in its Raman spectrum a strong fluorescent background when visible excitation is used, however, excitation in the near infrared (1064nm) permitted the observation of the Raman bands from the raw pigment with the main features placed at 1346, 1368, 1425, 1441 and 1626cm-1. Indian yellow identification was assured by1H and13C Nuclear Magnetic Resonance characterization and the complete assignment of the proton and carbon resonances was accomplished using heteronuclear single quantum correlation (HSQC), heteronuclear multiple bond correlation (HMBC), nuclear overhauser effect spectroscopy (NOESY) and1H-1H correlation spectroscopy (COSY). Scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) and X-ray fluorescence (XRF) analyzes were also conducted on a genuine sample of this historical pigment.
authors.affiliation: Institute of Chemistry, University of São Paulo, Av. Prof. Lineu Prestes, 748, Butantã, 05508-000 São Paulo, SP, Brazil; Interinstitutional Graduate Program in Museology (PPGMus-USP), University of São Paulo, Av. Prof. Almeida Prado, 1466, São Paulo, SP CEP 05508-070, Brazil. Electronic address: dlafaria@iq.usp.br.
authors.forename: Dalva L A
authors.initials: DLA
authors.lastname: de Faria
authors.affiliation: Department of Chemical and Forensic Sciences, University of Bradford, Bradford, West Yorkshire BD7 1DP, UK. Electronic address: h.g.m.edwards@bradford.ac.uk.
authors.forename: Howell G M
authors.initials: HGM
authors.lastname: Edwards
authors.affiliation: UMYMFOR and Departamento de Química Orgánica, Universidad de Buenos Aires, Pabellón 2, Ciudad Universitaria, 1428 Buenos Aires, Argentina. Electronic address: pcareaga@qo.fcen.uba.ar.
authors.forename: Valeria
authors.initials: V
authors.lastname: Careaga
authors.affiliation: L. Cornelissen & Son Ltd., 105 Great Russell Street, London WC1B 3RY, UK. Electronic address: nw@cornelissen.com.
authors.forename: Nicholas
authors.initials: N
authors.lastname: Walt
authors.affiliation: UMYMFOR and Departamento de Química Orgánica, Universidad de Buenos Aires, Pabellón 2, Ciudad Universitaria, 1428 Buenos Aires, Argentina. Electronic address: maier@qo.fcen.uba.ar.
authors.forename: Marta S
authors.initials: MS
authors.lastname: Maier
keywords: Artwork; Indian yellow; Pigment; Raman spectroscopy; Tartrazine