María Teresa Doménech-Carbó

Novel analytical methods for characterising binding media and protective coatings in artworks.

Since the first reported analytical studies and technical examinations of art and archaeological objects conducted in the late 18th century, analytical techniques and methods applied to the study of artworks have constantly grown. Among the materials composing the art object, organic compounds used as binding media or protective coatings have attracted the attention of the conservation profession given their noticeable ability for undergoing morphological and chemical changes on ageing. Thus, the aim of this paper is to review the most recent advances in the identification and determination of organic compounds present in art and art conservation materials. Immunofluorescence techniques have been proposed in recent decades as an alternative to the classical and simpler microchemical tests. Besides, a variety of instrumental techniques have also been improved in an attempt to enhance the sensitivity, repeatability and accuracy of the analytical results. Spectroscopic techniques, such as UV-vis, FTIR and Raman spectroscopy, have been coupled with light microscopes for these purposes. Synchrotron radiation FTIR microspectroscopy has also been successfully applied to the analysis of artworks. Mass spectrometry has also been increasingly used as a detector system coupled with a chromatographic device. Chromatographic methods have also improved in recent years. Paper and thin layer chromatographic techniques have been progressively replaced with gas chromatography (GC), pyrolysis-GC, high performance liquid chromatography and capillary electrophoresis. More complex proteomics hyphenated techniques, such as nano-liquid chromatography-nano-electrospray ionisation/collision quadrupole time-of-flight tandem mass spectrometry, have been recently applied to the identification and determination of proteinaceous binders. Microbeam analytical techniques have also been incorporated into the list of advanced instrumental techniques for art conservation purposes. Finally, a number of new instrumental techniques have been proposed as a suitable alternative to the conventional microscopy techniques for morphological studies.

Electrochemical Methods in Archaeometry, Conservation and Restoration

Application of Instrumental Methods in the Analysis of Historic, Artistic and Archaeological Objects.- Identification of Species by Electrochemical Methods.- Resolution of Multicomponent Systems and Speciation.- Quantitative Methods.- Electrochemical Basis of Corrosion of Cultural Objects.- Electrochemistry in Treatment and Conservation of Metal Artifacts.

Maya Blue as a nanostructured polyfunctional hybrid organic―inorganic material: the need to change paradigms

Maya Blue, an ancient nanostructured organic–inorganic hybrid material resulting from the attachment of indigo, a natural dye, to a phyllosilicate clay, palygorskite, has received considerable attention of late. Despite intensive research, several aspects remain unsolved, in particular the nature of the indigo–palygorskite association. Recent results suggest that the Maya Blue pigment is a complex system in which different topological isomers of various indigoid molecules attached to the palygorskite matrix coexist.

Dating Archeological Lead Artifacts from Measurement of the Corrosion Content Using the Voltammetry of Microparticles

A methodology for dating archeological lead artifacts based on the voltammetry of microparticles is described. This methodology is based on the comparison of the height of specific voltammetric features from PbO(2) and PbO corrosion products formed under long-term alteration conditions. Calibration of the method was performed with the help of a series of well-documented lead pieces from the funds of different museums of the Comunitat Valenciana (Spain) covering from the fifth century B.C. to present day. The variation of peak currents with the time of corrosion can be fitted to the same potential rate law as that found by Reich (α = 0.070 ± 0.005), using measurements on the Meissner fraction in the superconducting state of lead. The proposed electrochemical methodology enables the dating of archeological lead artifacts with a time-dependent uncertainty estimated to be ±150 years for the most ancient samples in this study.

From Maya Blue to “Maya Yellow”: A Connection between Ancient Nanostructured Materials from the Voltammetry of Microparticles

Financial support is gratefully acknowledged from the Generalitat Valenciana GV04B/441 I + D + I Project and the MEC Projects CTQ2004-06754-C03-01 and 02, CTQ2006-15672-C05-05/BQU, and CTQ2008-06727-C03-01 and 02/BQU, which are also supported with ERDEF funds. The authors would like to thank to Dr. Jose Luis Moya Lopez and Manuel Planes Insausti (Microscopy Service of the Universitat Politecncia de Valencia) for their technical support.

Identification of lead pigments in nanosamples from ancient paintings and polychromed sculptures using voltammetry of nanoparticles/atomic force microscopy

Voltammetry of nanoparticles coupled with atomic force microscopy was used to identify lead pigments in nanosamples proceeding from works of art. Upon mechanical attachment of few nanograms of sample to a graphite plate, well-defined voltammetric responses were obtained for lead orange, lead yellow, lead white, litharge, minium, Naples yellow, and tin-lead yellow, allowing for an unambiguous identification of such pigments. Atomic force images provide evidence for the occurrence of pigment-characteristic reduction processes accompanied by metal deposition on the graphite substrate. Electrochemical parameters are used for pigment identification. Application to the method for identifying lead pigments in different model binder+pigment specimens and pictorial samples from the canvas painting collection (anonymous, 17th century) of the Saint Joseph Church in Taormina (Italy), the frescoes painted by Antonio Acisclo Palomino y Velasco (1698) in the vault of the Sant Joan del Mercat church in València (Spain) and an anonymous polychromed sculpture (16th century) representing a Martyr Saint from Alacant (Spain) is described.

Layer-by-layer identification of copper alteration products in metallic works of art using the voltammetry of microparticles.

An in situ technique for layer-by-layer electrochemical analysis of solid surfaces using the voltammetry of microparticles is presented. The method is based on the determination of several shape-dependent parameters for voltammetric curves recorded at a graphite pencil working electrode in contact with the sample, all immersed into aqueous electrolytes. Repetitive square wave voltammetry and sequential application of constant potential reductive steps and voltammetric scans yield discernible responses for the corrosion products distributed in stratified layers on metal-based surfaces. This methodology is applied to identify alteration products of copper and copper alloys distributed in different layers in copper coupons submitted to different corrosive treatments and a contemporary brass sculpture.

Application of the voltammetry of microparticles for dating archaeological lead using polarization curves and electrochemical impedance spectroscopy

The application of the voltammetry of microparticles methodology to date archaeological lead artifacts, based on the time-dependent formation of different layers of lead oxides, whose relative amount can be estimated from polarization curves and electrochemical impedance spectroscopy (EIS), is presented. This approach is complemented by additional data using square wave voltammetry data. Calibration of the method was performed with the help of a series of well-documented, lead pieces from the funds of different Spanish museums, covering since the 7th century BC to nowadays.

Electrochemical identification of metal ions in archaeological ceramic glazes by stripping voltammetry at graphite/polyester composite electrodes

The electrochemical response of metal ions in different samples of coloured ceramic tin-lead glazes attached to graphite/polyester composite electrodes is described. In addition to the ubiquous signals for lead, reductive dissolution processes are followed by anodic stripping peaks for Co, Cu, Sb, Mn, Sn and Fe, enabling the direct identification of such elements in microsamples proceeding from archaeological glazed tiles from Valencia (Spain) workshops (16th-18th century). Additional anodic and cathodic peaks corresponding to redox processes involving metal species in solution generated during stripping processes are also used. Peak potentials, Tafel plots and shape parameters are used for characterising the different species.

Electrochemical Determination of the Fe(III)/Fe(II) Ratio in Archaeological Ceramic Materials Using Carbon Paste and Composite Electrodes

A method for determining the iron(III)/iron(II) ratio in ceramic materials based on microsample attachment to graphite/polyester composite electrodes is presented. This quotient is of considerable interest for determining the nature and firing conditions of the original materials in archaeological ceramics. The electrochemistry of iron in ceramic materials in acetic/acetate and Na2EDTA aqueous solutions is described in terms of reductive dissolution processes of iron(III) materials and oxidative dissolution processes of iron(II) ones. The iron(III)/iron(II) ratio is determined from peak area measurements in linear scan voltammograms performed in 0.10 M acetic/acetate buffer (pH 4.70) and 0.10 M Na2EDTA solutions. A second semiempirical method based on peak current measurements in repetitive cyclic voltammetry is also described. Both procedures were satisfactorily tested using a set of certified clays and applied to the study of a series of ceramic samples from Manises (Spain), dated on XVth and XVIIth–XVIIIth centuries. Results in agreement with SEM and XRD data are obtained.