Identification of indigoid dyes in natural organic pigments used in historical art objects by high‐performance liquid chromatography coupled to electrospray ionization mass spectrometry

Abstract

Pigments are among the most important components of historical paintings and textiles and their nature provides the unique character of color. They can be divided into two main groups: inorganic and organic, extracted from plants or animals. Their identification is a necessary stage in the conservation of art objects. Reversed-phase liquid chromatography with electrospray ionization mass spectrometry (ESI-MS) and UV/visible spectrophotometric methods were elaborated for the identification of indigoid (indigo, indirubin, isoindigo, isoindirubin) color components of natural dyestuffs and their natural or synthetic precursors (indican, isatin, indoxyl, 2-indolinone). ES-MS offers detection limits in the range 0.03-5.00 microg ml(-1) for the color compounds examined. The method developed made it possible to identify indigo and its isomers in genuine Indian indigo, indigo from woad and Tyrian Purple. It was applied to the identification of natural dyes on fiber from a 19th century Japanese tapestry, 'Cranes in the landscape'. A procedure based on freezing and grinding of a sample before the extraction of dyes from the textile was developed. The components of the extract obtained were identified after acidic hydrolysis as indigotin and methylene blue.

Extracting natural dyes from wool—an evaluation of extraction methods

“…Arraiolos recipes refer the use of weld and indigo to dye wool fibres in green hues [34]. The identification of indigotin as the chromatographic peak eluting at approximately 26.50 min was done based on its characteristic UV-Vis and mass spectra [12,44,45]. As reported in the literature [12,45] [2].…”

“…The identification of indigotin as the chromatographic peak eluting at approximately 26.50 min was done based on its characteristic UV-Vis and mass spectra [12,44,45]. As reported in the literature [12,45] [2]. The indigo made from I. tinctoria was of superior quality and was widely available in Europe in the eighteenth century [2].…”

H‐Point Standard Addition Method Applied to Voltammetry of Microparticles. Quantitation of Dyes in Pictorial Samples

“…From Equation 10, one can express the relative uncertainty associated with the mass fraction of A in the sample, e(r A ), as a function of the relative uncertainties of the quotients m/m R and (m AS / m R ) H : (11) The uncertainty associated to the quotient m/m R can be lowered by weighting relatively high amounts of sample and the reference material. Attributing the same uncertainty, Dm, for mass measurements, the relative uncertainty of the quotient m/m R satisfies [34,35]: (12) The error associated to that term is minimal for m/m R equal to unity.…”

Extraction of Indigo from Some Isatis species and Dyeing Standardization Using Low-technology Methods

“…Among the naturals dyes, indigo has been obtained from a variety of plant sources such as Indigofera tinctoria, Polygonum tinctorium, Nereum tinctorium and Isatis tinctoria (Gilbert and Cook 2001;Tozzi et al 2005). However, once its chemical synthesis from aniline was established, it has been largely produced by chemical industry and almost superseded natural indigo (Bechtold et al 2002;Puchalska et al 2004). Natural indigo is produced by fermenting the leaves of indigo bearing plants.…”