Application of thermomagnetometry to corrosion studies of archaeological iron

Summary Thermomagnetometry has been applied to mineralized archaeological iron samples and samples from accelerated corrosion tests. It has successfully quantified the degree of corrosion, measured by the loss of iron, as well as the amount of magnetite formed and water held in the corrosion and adhered soil layers. Thermomagnetometry, thermogravimetric analysis and differential scanning calorimetry have been applied to the reported corrosion products from archaeological iron. Fourier transform infra-red and Raman spectroscopies and X-ray diffraction analyses were undertaken on the residues and at intermediate heating stages, where the thermal analyses indicated, to identify the reaction products.     

Dynamic mechanical analysis (DMA), 13c solid state nmr and micro-thermomechanical studies of historical parchment

DMA and solid state ¹³C NMR techniques were used to measure historical parchment samples within the framework of the project (MAP) Micro Analysis of Parchment (EC contract No. SMT4-96-2101) in collaboration with the School of Conservation in Copenhagen. DMA was used in both thermal scan and creep modes. Thermal scans provided information on the transitions associated with the collagen polymer. Microthermal analysis was also used to obtain information on the topography and thermal conductivity of sample areas of 100 μm. Localised heating enabled measurements of softening transitions in the sample. This behaviour is influenced by the chemical composition of parchment. 13C NMR provided information on the carbon atoms associated with the polypeptide chains of the collagen in parchment. The behaviour of samples immersed in water and measured in DMA creep mode was used to measure the shrinkage behaviour of the parchment samples. The different but complementary techniques provided a means for characterising the physicochemical state of parchment samples. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermal analysis and the scientific conservation of cultural materials

Prior to treatment, letters dating from 1665–66 were characterised using SEM, FTIR, ESCA or XPS, TG, TMA and DLTMA. All three papers were similar in composition and were basically cellulosic materials. Two which had been sent from Lisbon contained trace amounts of Fe and Cu; these impurities were also present in a letter sent from Dublin. All three letters had been written with iron gall ink. The letter from Dublin had an additional feature in the ink in the form of small bright specks of mica. The papers were examined after conservation treatment using the above same techniques in an attempt both to determine and quantify any changes which had occurred during the treatment process. Scanning electron micrographs showed that propounced changes had occurred to the surfaces of the treated papers. With XPS it was possible to measure the change in the surface composition of the papers which occurred on treatment. It was also found that the treatment reduced the thermal stability of the papers in all three cases.     

Environmental Research for Art Conservation and Assessment of Indoor Conditions Surrounding Cultural Objects

This paper describes the results and conclusions of research directed towards the development and evaluation of a chemical sensor which would provide information on the quality of indoor environments surrounding cultural objects. In our case these objects were paintings housed in major European galleries and the main objective is their preservation through an improved understanding of their microenvironment. The concept was to prepare and expose test tempera paintings which would behave as dosimeters and integrate the environmental response at these locations. Artificial ageing of similar samples was performed to provide a means of calibrating the test paintings. Samples from the test paintings were compared with artificially aged samples and this enabled the sites to be ranked in terms of their suitability for exposure of cultural objects. Additionally, novel methodology involving piezoelectric sensors was designed for monitoring the relative humidity and temperature of the microenvironment of paintings. Dielectric techniques were also used for measuring the effect of relative humidity fluctuations on artists' materials and novel non-invasive dielectric techniques in the microwave region were used for the determination of their moisture content. This revised version was published online in August 2006 with corrections to the Cover Date.     

The use of thermal and spectroscopic methods to study chemically modified materials

The application of thermal and spectroscopic techniques in the characterisation of chemically modified materials is illustrated with several examples: ethylene vinyl acetate (EVA) copolymers which had been hydrolysed under alkaline conditions, amosite asbestos fibres which had been reacted with alkyldimethylchlorosilanes, and a polymeric composite material which had been affected by moisture.The authors acknowledge the following for assistance in the project: Rhona MacBeth, Conservator, Courtauld Institute of Art and presently at the Boston Museum of Fine Arts, for the TMA measurements, conditioning of composite samples, and useful discussions. PL-Thermal Sciences (John Gearing for the DETA measurements on EVA). PL-Thermal Sciences (Epsom Laboratories) for the use of Dynamic Mechanical Thermal Analysis equipment.     

Prediction of thermal stability of fresh and aged parchment

The hyphenated thermal analysis-mass spectrometry technique (TA-MS) was applied for the investigation of the thermal behavior of reference and aged parchment samples. The kinetic parameters of the process were calculated independently from all recorded TA and MS signals. The kinetic analysis showed the distinct dependence of the activation energy on the reaction progress. Such behavior is characteristic for the multistage mechanism of the reaction. The comparison of the kinetic parameters calculated from the different signals i.e. TG, DSC, MS for H₂O, NO and CO₂, however, indicated that they were differently dependent on the aging of the sample. For the parchment samples, the aging almost does not change the kinetics of the decomposition calculated from the DSC data: the influence of aging seems to be too negligible to be detected by these techniques. On the other hand, the much more sensitive mass spectrometric technique applied to the kinetic analysis allowed monitoring of visible changes in the thermal behavior of the parchment samples due to the aging process. The influence of aging was especially visible when the MS signals of water and nitric oxide were applied for the determination of the kinetic parameters. The applied method of the kinetic analysis allowed also the prediction of the thermal behaviour of reference and aged parchment samples under isothermal and modulated temperature conditions. Presented results have confirmed the usefulness of thermoanalytical methods for investigating behaviour of such complicated systems as leather or parchment.     

Thermal analysis of model and historic tapestries

Dynamic mechanical thermal analysis (DMTA), differential scanning calorimetry (DSC) and thermogravimetry (TG) have been used to characterise model tapestries, especially woven for the EC-funded project (MODHT) and to historic tapestries in royal palaces and museums. Modulus values of woollen threads from model tapestries are reported and the effects of traditional dyeing and mordanting processes quantified. TG, particularly of black woollen threads showed alterations in thermal stability. Tests of creep on immersion in water and subsequent heating to 90°C and on exposure to a controlled relative humidity programme were also used to rank these effects. Modulus values of historic woollen samples were also obtained and DSC studies of model and historic silk samples are reported together with preliminary atomic force microscopy (AFM) images of silk fibres.     

Development of standard paint films based on artists' materials

The degradation of art objects is caused by the combination of all indoor environmental factors. To investigate the deterioration processes in paintings and at the same time to design a risk assessment system, chemical sensors based on artist's materials are developed. Therefore standard paint films of egg yolk tempera with lead white 2PbCO₃·Pb(OH)₂, azurite 2CuCO₃·Cu(OH)₂ or smalt were investigated. With accelerated ageing experiments the simulation of natural degradation processes is aimed. First markers for chemical changes were found in the FTIR and TG/DSC measurements.Gratitude is expressed to the European Union for the financial support under the project SCICULT, Human Capital & Mobility. The authors also thank A. Portmann, Institute of Inorganic Chemistry, University of Zürich, for the SEM investigations.     

A study of the mechanical and surface properties of oil paint films treated with organic solvents and water

Mechanical and surface properties of paint films treated with organic solvents and water have been investigated using a range of thermomechanical and dielectric techniques together with Fourier transform infrared spectroscopy and scanning electron microscopy. Changes in the nature of the surface after treatment were observed. The effect of water, propan-2-ol and propanone (acetone) immersion for 24 hours, and swabbing for a few minutes, on naturally aged 12 years old samples of lead white/linseed oil and burnt sienna/linseed oil could be measured directly in terms of change in the shear modulus of the paint films together with the accompanying change in the ratio of viscous to elastic components present in each system. Generally, the solvent-treated films became harder and showed reduced viscous components, whereas the water-treated samples became softer. There was a change in the dielectric properties of the leached films which pointed to the polar nature of the leachings. FTIR diffuse reflectance spectra supported this conclusion.

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Zusammenfassung Mittels einer Reihe von thermomechanischen und dielektrischen Verfahren sowie FT-IR-Spektroskopie und Scanning-Elektronenmikroskopie wurden die mechanischen und OberflÄcheneigenschaften von mit organischen Lösungsmitteln und Wasser behandelten Anstrichfilmen untersucht. Nach der Behandlung konnte eine VerÄnderung der OberflÄchenbeschaffenheit beobachtet werden. Der Effekt von 24-stündigem Eintauchen in bzw. paar minütigem Abtupfen mit Wasser, Propan-2-ol und Propanon (Azeton) von natürlich gealterten, 12 Jahre alten Proben von Bleiwei\/Leinöl und gebrannter Sienaerde/Leinöl konnte als Funktion des Schubmodules des Anstrichfilmes gemessen werden, begleitet von einem übergang von viskosen zu elastischen Komponenten in jedem System. Im allgemeinen wurden die lösungsmittelbehandelten Proben hÄrter und wiesen weniger viskose Bestandteile auf, wÄhrend die wasserbehandelten Proben weicher wurden. Es trat auch eine Änderung der dielektrischen Eigenschaften der ausgelaugten Filme auf, was auf den polaren Charakter des Auslaugungsvorganges hinweist. FT-IR Remissionsspektren bekrÄftigten diese Schlu\folgerung.

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Paper was presented at the 13th International Congress of the International Institute for Conservation of Historic and Artistic Works (IIC) in Brussels, Belgium, 3–7 September 1990 on the subject Cleaning, Retouching and Coatings: technology and practice for easel paintings and polychrome sculpture.     

The hydroxyl content of silica gel

Thermogravimetric analysis of silica gel has shown that the loss in weight between 30° and 910°C can be quantitatively explained on the basis of water being lost from three distinct and different populations of sites on the silica gel surface. The results indicate that the site energies of the three different populations are randomly distributed and, consequently, the resulting weight loss steps from each population can be described by the integral of a simple normal distribution with temperature. The calculated weight loss obtained by assuming three different site-groups having randomly distributed adsorption energies is, within experimental error, coincident with the experimental data. It is also shown that the water evolved from the second population of sites originates from strongly bound water and may also contain water generated by the condensation of (geminal) silanol groups contained in the overlapping and neighbouring population.