, Volume 61, Issue 7–8, pp 403–408 | Cite as

Identification of Indigo Dyes in Painting Layers by Pyrolysis Methylation and Silylation. A Case Study: “The Dinner of Emmaus” by G. Preti



Reactive pyrolysis, under methylating or silylating conditions, in combination with gas chromatography-mass spectrometry (GC-MS) was evaluated as an analytical method for the detection of indigo dyes in painting layers. Samples with the addition of tetramethylammonium hydroxide (TMAH) or hexamethyldisilazane (HMDS), for pyrolysis/methylation and pyrolysis/silylation experiments, respectively, were pyrolysed at 600 °C by means of a heated filament pyrolyser and the evolved products were analysed on-line by GC-MS. Methyl and silylated pyrolytic markers, related to 2-aminobenzoic acid and the indoxyl moiety, were established from the analysis of synthetic indigo, neat or as a pigment of artificial painting layers containing a siccative oil. The occurrence of these markers was investigated in a real sample, taken from the painting “The dinner of Emmaus” by G.Preti (XVII century), in order to identify the blu pigment. Positive identification of indigo was achieved by pyrolysis/silylation and confirmed by RAMAN spectroscopy.


Gas chromatography-mass spectrometry Pyrolysis Methylating, silylating conditions Indigo dyes in layers of ancient paint 


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Copyright information

© Friedr. Vieweg&Sohn/GWV Fachverlage GmbH 2005

Authors and Affiliations

  1. 1.Laboratory of Analytical ChemistryC.I.R.S.A.-University of BolognaRavennaItaly
  2. 2.Department of ChemistryUniversity of FirenzeSesto (Firenze)Italy

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