ABOUT THE ElcHer VOLTAMMOGRAM DATABASE INITIATIVE
The HelcHer V Voltammogram Database is a dynamic compilation of reference voltammograms of cultural heritage materials contributed by the members of the Group Electrochemistry for Heritage. The database currently contains over 100 voltammograms of minerals, inorganic and organic pigments, mixtures and unclassified materials. In a number of cases the voltammogram is accompanied of IR spectrum, visible spectrum, X-Ray spectrum, light microscopy photograph and electron microscopy photograph.
Voltammograms are formatted with a customized format to incorporate graph. Each file is an independent record.
Voltammograms are publicly viewable, keyword searchable and printable. Digital file downloads of all spectra are available to not-for-profit institutions and individuals.
ElcHer COMMITTEE
Chair
- Prof. Dr. Antonio Doménech-Carbó, Dpto. Química analítica. Universitat de València, Burjassot, Spain
- Prof. Dr. María Teresa Doménech-Carbó, Instituto Universitario de Restauración del Patrimonio, Universitat Politècnica de València, Valencia, Spain.
Current members
- Dr. Laura Osete-Cortina, Instituto Universitario de Restauración del Patrimonio, Universitat Politècnica de València, Valencia, Spain.
INSTRUMENT AND ANALYSIS DETAILS
Voltammetry of microparticles
Electrochemical experiments were performed at 298 K in a three-electrode cell after 10-15 min bubbling of Ar. Square wave voltammograms (SQWVs) and complementary cyclic voltammograms (CVs) were obtained with a CH 660I equipment. Paraffin-impregnated graphite working electrodes were dipped into the electrochemical cell so that only the lower end of the electrode was in contact with the electrolyte solution. This procedure provides an almost constant electrode area and reproducible background currents. A AgCl (3 M NaCl)/Ag reference electrode and a platinum-wire auxiliary electrode completed the conventional three-electrode arrangement. 0.50 M acetic acid plus sodium acetate aqueous buffer (pH 4.75) and 0.10 M HCl were used as electrolytes.
Square wave voltammograms at pigment-modified graphite bars (Alpino, Masats SL, Spain) immersed into 0.25 M HAc/NaAc aqueous solution at pH 4.75. Negative-going scan. Potential step increment 4 mV; square wave amplitude 25 mV; frequency 5 Hz.
Square wave voltammograms at pigment-modified graphite bars (Alpino) immersed into 0.10 M HCl aqueous solution. Potential step increment 4 mV; square wave amplitude 25 mV; frequency 5 Hz.
FTIR spectroscope
FTIR-1
The IR spectra in the ATR mode of the powdered samples were obtained using a PerkinElmer, model Spectrum BX, program Spectrum Fourier-transform infrared spectrometer with an FR-DTGS (fast recovery deuterated triglycine sulphate) temperature-stabilised coated detector and a MKII Golden Gate Attenuated Total Reflectance (ATR) accessory. A total of 32 scans were collected at a resolution of 4 cm-1 and the spectra were processed using the OPUS/IR software.
FTIR-2
The IR spectra in the ATR mode of the powdered samples were obtained using a Vertex 70 Fourier-transform infrared spectrometer with an FR-DTGS (fast recovery deuterated triglycine sulphate) temperature-stabilised coated detector and a MKII Golden Gate Attenuated Total Reflectance (ATR) accessory. A total of 32 scans were collected at a resolution of 4 cm-1 and the spectra were processed using the OPUS/IR software.
UV-Vis spectrophotometer
Diffuse reflectance spectra in the UV and visible regions of the samples finely powdered were obtained using a Perkin Elmer Lambda 1,050 recording double-beam spectrophotometer with a special back-scattering configuration. Reflectance measurements were carried out in the range from 200 to 850 cm−1. The device allows a 1 nm wavelength resolution and a precision on the reflectance factor equal to 0.1%.
In order to perform the reflectance measurements, a few micrograms of sample were homogenized with a drop of nujol oil in a small agate mortar. The paste formed was applied as a thin film on a disk of paper Wathman 42 with the help of a scalpel. Thus, a circular surface ( Æ = 5 mm) was covered of a homogeneous layer of pigment ready for measuring. A second disk in which pure nujol oil was applied was used as blank for subtracting to the samples and thus suppressing the contribution of the nujol used as binder to the reflectance spectrum.
Scanning electron microscope-x-ray microanalysis
Chemical composition of the minerals was obtained using a Jeol JSM 6300 scanning electron microscope operating with a Link-Oxford-Isis X-ray microanalysis system. The analytical conditions were: 20 kV accelerating voltage, 2x10-9A beam current and 15 mm as working distance. Samples were carbon coated to eliminate charging effects. Quantitative microanalysis was carried out using the ZAF method for correcting interelemental effects. The counting time was 100 s for major and minor elements. Element percentages were generated by ZAF software on the Oxford-Link-Isis EDX with INCA software.
Light microscope
Polarized light microscope Leica DM2500 P (Leica Microsystems. Heidelberg, Germany). Leica Digital FireWire Camera (DFC) with Leica Application Suite (LAS) sotftware has been used for acquiring and processing the digital images.
ABOUT THE SEARCH
Keyword(s) search is a full search of all text fields in the database. Please note that keyword(s) may appear in the filename, common name, supplier, material type or data type field.
The search provides the voltammograms of the selected materials. Complete view of the voltammogram is obtained by clicking on the voltammogram. Details of sample, such as chemical name and working conditions are provided as figure caption. In most materials a list of accompanying spectra and photographs is included at the bottom of the voltammogram. These graphs and images can be also accessed by clicking on the miniaturized figure.
HelcHer Data Base General Format
Filename
Common name of the material followed by two digits in order to distinguish materials of the same chemical composition and different provenance or supplier and followed by the acronym of the data type (vide infra). For example: Ochre yellow 01_SQWV (French), Ochre yellow 02_SQWV (Italian)
Common name
Common, generic or mineral name of the material are provided in English and Spanish language. For example: Smalt, esmalte, azul esmalte.
Supplier
Provenance or manufacturer of the material. For example: Kremer, Windsor & Newton
Material type
The materials included in the data base are classified in the following types:
Inorganic pigments: natural or synthetic elemental substances, oxides, salts or clayey minerals used as pigments.
Organic pigments: metallic complexes and organic compounds used as pigments or dyes.
Mineral: natural inorganic minerals rarely used as pigments and corrosion products occurring as salts of organic and inorganic acids.
Mixtures: Materials with constituents from multiple classes (such as paint films and composites) and commercial products and formulations. For exam
Data type
Other details of interest such as chemical name, trade names; material sources or working conditions are provided as figure captions.
In the HelcHer database: square wave voltammogram (SQWV), cyclic voltammogram (CV), (IRS) Infrarred absorption spectrum, (UVS) Visible spectrum, (XRS) x-Ray spectrum, (XBEP) backscattered electron photograph, (XEP) secondary electron
List alphabetical of pigments and minerals
Anglesite
Atacamite
Atramentum
Azurite
Bavatian green earth
Brochantite
Burnt green earth
Burnt umber
Carpathian gold ochre
Celadonite green earth
Cerussite
Chrome orange
Chrysokolla
Cinnabar
Cotunnite
Cuprite
Egyptian blue
Epidote
French ochre
Gold ochre
Green earth
Han blue
Iron glimmer
Iron oxide red
Lead tin yellow
Lead White
Limonite Litharge
Madder
Malachite
Manganese black
Manganese grey
Mars orange
Mars yellow
Massicot
Minium
Naples yellow
Natural sienna
Persian red
Ploss blue
Pyrite
Raw Sienna
Raw umber
Red clay
Red earth
Red ochre
Smalt
Translucent brown-orange
Vagone green earth
Venetian red
Verdigris
Verona green earth
Vesuvianite
Vivianite
White lead
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ElcHer - 2014 Universitat Politècnica de València, Universitat de València by María Teresa Doménech Carbó, Antonio Doménech Carbó is licensed under a Creative Commons Reconocimiento-NoComercial-SinObraDerivada 4.0 Internacional License.