Raman, X‐Ray Fluorescence Spectroscopies and Graphene Oxide Modified Screen Printed Electrodes to Identify the Pigments and Earth Present in Ancient Leather Samples

Abstract

Micro‐Raman and X‐Ray Fluorescence combined with electrochemical techniques proved to be suitable for the unambiguous identification of the green pigment in a very deteriorated historical leather. The colouring matter resulted in a mixture of blue and yellow. Raman identified the blue indigo, whereas iron and arsenic were identified by XRF. The redox status of these two elements was investigated by Square Wave Cathodic Stripping Voltammetry (SWCSV). Results demonstrated the presence of As(III), probably As2S3 (orpiment), and Fe(III), characterising the red earths. The quantitative results obtained by SWCSV were also confirmed for Fe and As by ICP‐MS (Inductively Coupled Plasma Mass spectrometry). Voltammetric techniques, applied here for the identification of the redox status of the elements, contained in pigments, are useful to understand two important aspects: the chemical‐physical composition of the colors and the best strategy to be applied for the preservation of the pigments in ancient/deteriorated artwork objects.

Smart Electrochemical Portable Tools for Cultural Heritage Analysis: A Review

“…The third prototype of the review is represented by SPEs chemically modified with GO, for the identification of the pigments and earth present in ancient leather samples [16]. SPEs modified with GO were assembled by Valentini, et al; in reference [16], where GO was synthesized by the unzipping reaction of Single Wall Carbon Nanotubes (SWCNT, used here as precursor), according to reference [16]. SPEs were chemically modified by drop-casting, using 5 µL of 1 mg/mL GO-ethanol dispersion, and leaving the solvent to evaporate at room temperature.…”

“…In ( b ): ( A ) represents the calibration for As(III), ( B) represents the calibration for Fe(III), ( C ) shows FE-SEM/EDAX micrographs, before (left image) and after (right image) GO modification of SPEs. Reproduced and reprinted with permission from [16].…”

“… a: two-sided t-test to compare means from heteroscedastic data. Data reported on Table 3 are reproduced and reprinted with permission from [16]. …”

“…Portable electrochemical Surface Enhanced Raman Spectroscopy (SERS) [14] is suitable for a highly sensitive and selective diagnosis of organic layers; miniaturized electrochemical cells of the Bragg model [15] are suitable for in situ synchrotron X-ray measurements on heterogeneous CH alloys with corroding surfaces. Screen-Printed Electrodes (SPEs), chemically modified with Graphene Oxide (GO), are extremely highly performing for redox status identification of pigments and earth present in ancient leather samples [16]. Paraloid B72 film-modified microelectrodes are applied for detection of inorganic pigments in paintings, by using cyclic voltammetry and differential-pulse-stripping voltammetry [17].…”

Present Status and Perspectives of Graphene and Graphene‐related Materials in Cultural Heritage

“…GO properties have already been tested for the development of screen‐printed electrodes to discriminate metals (e.g., Fe) and metalloid compounds (e.g., As): this voltammetric approach was used to identify the redox state of Fe and As. [ 210 ] The determination of the redox status of these two elements within the pigments, [ 211 ] together with their speciation, is important for understanding the physico‐chemical properties of artworks even when present in trace amounts. [ 212 ] This determination can be carried out by removing a tiny amount of sample from the artwork, [ 213 ] or by direct contact of the sensor with the pigment; in this case, the electrolytic contact is obtained with hydrogels, paving the way for the implementation of screen‐printed electrodes modified with GO in already existing restoration and conservation methodologies.…”