Neil S. Cohen

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.

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.

Characterisation of Leather Samples by Non-invasive Dielectric and Thermomechanical Techniques

A description is given how the dielectric coaxial technique measuring in the microwave region has been used for monitoring drying processes in leather samples. It is also shown how the coupling of this technique together with dynamic mechanical analysis enables the simultaneous recording of changes inthe dielectric properties, related to the moisture content of the material, together with the mechanical properties as a function of time or temperature. The samples studied include unaged and artificially aged goat and calf leathers. Measurements using the dynamic mechanical analyser are presented over a range of temperature which includes the shrinkage temperature. During the drying process, values of mechanical modulus or displacement and dielectric permittivity are recorded as a function of time or temperature which includes the temperature range of leather shrinkage, and from previous research report of Larsen [1] this has been associated with the chemical state of the leather samples.

Thermal analyses of selected soil samples from the tombs at the Tianma-Qucun site, Shanxi, China

Abstract This paper describes a study of selected soil samples from three of the tombs at the Tianma-Qucun site, Shanxi province, China, using thermogravimetry and differential scanning calorimetry. The results of the analyses indicate that these soil samples are calcite-rich and contain a few percent of organic matter. The soil from the location of one of the tombs was found to have less calcite than the soil from the other two tombs. There was, however, only a small difference in organic matter in the soils from the different tombs. Results for soil samples taken from regions in the proximity of archaeological objects, however, demonstrated that the microenvironment as characterised by the soils for objects in various locations of the one tomb varied. Some evidence for the presence of charcoal and collagen based material was found.

Microclimate monitoring of indoor environments using piezoelectric quartz crystal humidity sensors

The aim of this paper is to describe indoor microclimate monitoring at two different locations, Sandham Memorial Chapel, in Hampshire, England, and the castle El Alcázar, in Segovia, Spain. Piezoelectric quartz crystal sensors with novel humidity sensitive poly(ethyleneimine) coatings and Pt resistance thermometers were used to measure the relative humidity (RH) and temperature gradients across one of the paintings of the British artist, Stanley Spencer, housed in Sandham Memorial Chapel. The measurement period extended from December 1997 to September 1998. Each coated crystal was set in its own housing from which temperature and RH measuring circuits were connected via a cable to the computer. The 9 month monitoring period incorporated the range in seasons from winter through to autumn. Between December and February the RH at the back of the painting was found to be lower than that at the front. In March and April the reverse was true. Additionally, there were large spikes in the data in some of the months for both RH and temperature, probably caused by direct sunlight falling on the sensors. At the second site monitoring was performed for a shorter period, from December 1997 to early January 1998. It served, however, to show that abrupt changes can occur in the microclimate surrounding the painting. These fluctuations can with time lead to alterations to the paint surface and result eventually in cracking and damage to the art work.

THERMAL ANALYSIS OF NEW, ARTIFICIALLY AGED AND ARCHIVAL LINEN

The thermal degradation of new, and artificially aged fine Ulster linen and archival linen specimens from 19th century paintings were compared using thermogravimetric analysis and differential scanning calorimetry. Thermal degradation data from new and artificially aged linen were found to be similar in nature. Archival specimens showed a decreased major degradation temperature, an increase in char remaining at the end of the experiment and some evidence of a depressed glass transition temperature. These indicate natural ageing through chain scission. Evidence of a two-stage degradation process was observed in some archival specimens suggesting that an unknown additive was present.