Gary M. Foster

Measurement of shrinkage behaviour in leather and parchment by dynamic mechanical thermal analysis

The mechanical behaviour of modern and historic parchment and leather samples through their shrinkage temperature is described. The measurements are made possible by the novel modification of a standard dynamic mechanical thermal analyser (Rheometric Scientific DMTA Mk3) to enable experiments to be conducted on samples immersed in water. A sample of parchment was clamped in tensile mode under a small static applied force. The temperature of the water could be controlled and thus it was possible to heat the sample and monitor the change in its displacement as it passed through the shrinkage temperature. Information could therefore be obtained on the percentage shrinkage and the temperature range over which it occurred. Furthermore, the method also provided useful information on the expansion or contraction of the samples on initial immersion in water, which relates to ease of sample wettability, and on the changes during drying process and rehydration.

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.

Dosimetry of paintings : determination of the degree of chemical change in museum exposed test paintings (lead white tempera) by thermal analysis and infrared spectroscopy

Thermoanalytical (DSC and TGA) data on the basic lead carbonate pigment alone have been previously published [J. Chem. Soc., Dalton Trans. (1996) 3639]. This paper draws attention to the modifying effect of basic lead carbonate on the thermal stability of the paint medium, and on the degradation of the paint medium under controlled light ageing conditions. The various light dosages received by the samples were found to produce differences in the shape of the leading edge of the DSC curves. Quantification of the data shows that there is a systematic trend, i.e. the difference in the leading edge of the DSC curve, with respect to the control sample, increases with the duration of light exposure of the samples. In the natural ageing of the samples exposed in various galleries for a period of 9 months, the dominant change is a shift in the overall peak. Changes in artificially and naturally aged samples were also identified by Fourier transform infrared spectroscopy. The broadening of the carbonyl peak due to the formation of lipid oxidation products could be quantified to determine the degree of chemical change.

Dosimetry of paintings: determination of the degree of chemical change in museum exposed test paintings (azurite tempera) by thermal and spectroscopic analysis

Abstract This paper describes the effects of accelerated artificial and natural ageing on samples of azurite paint tempera prepared according to traditional early Italian recipes. The pigment used was basic copper carbonate in the form known as azurite and this was mixed using whole egg tempera medium. Artificial and natural ageing of the dosimeters was performed using controlled ageing chambers and selected sites of varying environmental conditions. The effects of ageing were quantified using a number of analytical techniques, which include the following: thermal analysis (DSC and TGA), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The data were then compared with those obtained from samples which were naturally aged by exposure in selected European art galleries and historic castles for a period of 9 months. It was found that the changes observed on artificial light ageing alone were minimal. Mass spectrometry (DTMS) showed that samples had already undergone oxidation during the curing stage of 3 months [O.F. van den Brink, G.B. Eijkel, J.J. Boon, Thermochim. Acta 360 (2) (2000), this proceedings]. There were, however, measurable differences in the samples that had been subjected to thermal and pollutant ageing, and this was used to rank the sites.

Dosimetry of paintings: determination of the degree of chemical change in museum exposed test paintings (smalt tempera) by thermal analysis

Abstract One of the main concerns of conservators and curators is to find a method for evaluating the damage incurred by works of art in major galleries, historic houses, and castles with differing indoor environmental conditions. For this purpose, test tempera paintings were prepared and exposed at selected sites. The test paintings act as dosimeters and integrate the contributions from a range of factors which determine the overall environmental hazard to which paintings are exposed. Subsequent analysis of the test paintings involved an interdisciplinary approach using mass spectrometry (FOM Institute, the Netherlands), thermal analysis (Birkbeck College, UK) and non-invasive spectroscopic analysis (CNR–IROE, Italy). These techniques gave a measure of the physicochemical change and hence the resulting damage. In this paper, the thermoanalytical data will be presented, in particular of smalt tempera. Prior accelerated ageing of similar test paintings using controlled conditions was also performed to provide a comparison between artificial and natural ageing and a means for calibrating the test paintings.

Thermal analysis of model and historic tapestries

SummaryDynamic mechanical thermal analysis (DMTA), differential scanning calorimetry (DSC) and thermogravimetry (TG) have been used to characterize 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.

Controlled temperature and relative humidity dynamic mechanical analysis of paint films

A description is given of modifications to a dynamic mechanical analyser (DMA) to allow controlled relative humidity (RH) experiments to be performed under isothermal or thermal scanning conditions. Free film samples of polyester melamine paints (under-cured, normal-cured and over-cured) were supplied and the viscoelastic properties measured in the tensile mode of the DMA. A reduction in the glass transition temperature (Tg) of up to 10°C was found as the controlled RH was increased.