Session One (Thursday morning)
Chair: Mr. Boris Pretzel (V&A Museum)
Hazel Newey, Head of Conservation, Science Museum
Biaxial Tensile Testing of Paintings on Canvas
Christina Young, Imperial College
Effect of Cleaning on the Surface Morphology of Plastics
Sheila Fairbrass, Imperial College
The Atmospheric Corrosion of Lead: A Surface Study
Leon Black, Bristol University
Conservation of Aluminium and its Alloys
Chris Moynehan, Bristol University
Session Two (Thursday afternoon)
Chair: Dr. Joyce Townsend (Tate Gallery)
Chromatographic Studies of Drying Oils
Caroline Mathews, Birkbeck College
The Techniques of English Medieval Wall Painting: New Discoveries and Conservation Implications
Helen Howard, Courtauld Institute
Tin-Relief Decoration and Medieval European Art, 1250-1550
Jilleen Nadolny, Courtauld Institute
Moisture Beneath the Surface: Effects of the Exterior Environment on Porous Materials
Robyn Pender, Courtauld Institute
Session Three (Friday morning)
Chair: Ms. Yvonne Shashoua (British Museum)
Assessment of EDTA as a Cleaning Reagent for Stained Glass Weathering Products
Maggie Hood, University of Strathclyde
Conservation of Waterlogged Wood
Theo Skinner, National Museum of Scotland
The Science of Art
Sarah Vallance, University of Northumbria
Effects of Cleaning on the Surface Morphology of Plastics (abstract)
The development of Laser Surface Profilometry has allowed detailed inspection and measurement of the surface of objects at micron level without the need for sample preparation. This talk will focus on some of the ageing characteristics of PVC.
Samples of PVC were exposed to UV radiation and also natural sunlight using the Blue Wool Standard as a guide to dosage, and the surfaces were examined with the profilometer. They were left in situ under the laser while the surfaces were swabbed with distilled water and then re-examined for changes in surface morphology.
Preliminary results indicate that surface deformation is visible after the light dosage needed to fade Blue Wool Standard 4. At Blue Wool Standard 5 surface de-lamination can occur.
A second study using the percent reflectance of the laser from the surface is being carried out to determine whether it is possible to identify cleaning materials left on the surface after conservation.
The Atmosphereic Corrosion of Lead - a Surface Study (abstract)
Lead is used extensively as a roofing material in the United Kingdom, particularly on historic buildings. Upon exposure to the outdoor environment lead develops a grey patina, resulting in the metal's characteristic appearance. This patina may be non-adherent, and so may result in 'run-off' staining of adjacent areas, thus spoiling the aesthetic appeal of a lead roof.
It is a desirable requirement of a lead patina that it be insoluble, stable, and adherent, thereby improving the lifetime and appearance of a roof and adjacent areas. This project seeks to determine the role of various environmental parameters in the formation of a lead patina.
Various surface analytical techniques have been used, but Laser Raman Spectroscopy and X-ray Photoelectron Spectroscopy have proved ideal for the identification of lead compounds, and the subsequent determination of the surface composition. The analysis of field-exposed samples has formed the bulk of the study. The effects of time, environment, alloy composition, and initial date of exposure have been investigated. The interaction of the lead in contact with various woods has also been investigated.
Facilities at the Interface Analysis Centre enable very thin patina films to be analysed. This has enabled the analysis of samples after much shorter periods of exposure than is possible by conventional techniques, providing information on the initial patination processes occuring on the lead surface.
The initial corrosion processes can be simulated under controlled conditions to observe patination on an atomic layer scale. The controlled oxidation of lead has been performed, and it is hoped that future work will examine the effects of other corrosive gases such as SO2 and NOx.
Conservation of Aluminium and its Alloys (abstract)
Although aluminium is a reactive metal, it is generally protected by a thin layer of passive oxide on its surface. Localised corrosion of aluminium will consequently take place at defects in the passive film, causing pitting. When this takes place in crevices it can be particularly destructive. It is thus necessary to treat aluminium objects with compounds to inhibit the corrosion reactions. Many commercial inhibitors exist, but are often unsuitable for conservation work because of their toxicity or irreversibility. The aims of this project are to develop and characterise the behavior of a suitable inhibitor for use on the Science Museum's collection of aircraft. To this end, a series of long-term atmospheric corrosion tests have been initiated, and work is underway on
Chromatographic Studies of Drying Oils (abstract)
An analytical system for the identification of oils in works of art is being developed, based on chromatographic techniques.
At the present time identification of dried oils is usually carried out by determination of the ratio of palmitic to stearic acids by gas chromatographic analysis. The current work is looking at ways of improving upon this technique by investigating the reactions undergone in the drying process and the utilisation of some of the small reaction products in order to facilitate identification.
From the information gained, a system based on chromatographic and electrophoretic techniques is being developed. Initially this is concentrating on the readily soluble components of dried oils with gel permeation chromatography and high performance liquid chromatography being used for the analysis of mono- and di- carboxylic acids and capillary gas chromatography for the analysis of unreacted triacylglycerols. Miniaturisation of the liquid chromatography system is also being undertaken in order to facilitate the analysis of very small samples. Electrophoretic techniques are being investigated as an alternative to chromatography for these analyses.
The Techniques of English Medieval Wall Painting: New Discoveries and Conservation Implications (abstract)
The technical sophistication of English medieval wall paintings has been fully established during the first four years of a research project which set out to systematically study all aspects of technique. The main finding, which is particularly relevant to conservation treatments, is that wall paintings are generally more complex than previously supposed and that mixed media are frequently employed. Although a high degree of sophistication might be expected in Gothic paintings - such as those in the feretory of St. Albans Cathedral which have a complex layer structure, fragile lakes and glazes, and appear, not unexpectedly, to have been executed in an oil medium - similar technical refinements have also been found in earlier paintings of the Romanesque period. The scheme of c. 1440 in St. Gabriel's Chapel, Canterbury Cathedral - always presumed to have been painted in true fresco - has been shown to have a complex layer structure with lead white grounds and vermillion glazes and most significantly, to be painted with mixed media. It is increasingly clear that wall paintings such as these, which undergo conservation relatively frequently, are - unless the nature of the technique is fully understood - extremely vulnerable to inappropriate conservation treatments. This paper will report on recent technical discoveries and their implications for conservation.
Tin-Relief Decoration and Medieval European Art, 1250-1550 (abstract)
To date, the extensive use of tin in the polychromy and paintings of the high and late Middle Ages has not been fully recognised. The physical properties of tin were widely exploited by medieval artists, primarily to aid in the mass production of relief applications. Beaten into thin sheets of foil, tin was imprinted with low relief designs, then glazed or gilded, and used to embellish everything from paintings to interior architecture. Due to problems related to the degradation of tin, such decorations are often in poor condition and retain little of their original splendour. This talk will describe the various uses of tin in polychromy and trace the history of the application of these techniques in the major art producing centres of central Europe.
Moisture Beneath the Surface: Effects of the Exterior Environment on Porous materials (abstract)
This paper will discuss the damage phenomena associated with the sorption of atmospheric moisture within the porous supports of wall paintings. A series of experiments is being undertaken with the aim of characterising the effect of the environmental parameters of air movement, temperature, and relative humidity on supports of differing porosities and surface characteristics. The aim of the study is to provide a methodology for future investigations, with the intent of relating those parameters amenable to environmental monitoring with the actual behavior of in situ wall paintings.
Assessment of EDTA as a Cleaning Reagent for Stained Glass Weathering Products (abstract)
The effect of EDTA on stained glass has been examined using flame atomic absorption spectrometry (FAAS) and inductively coupled plasma-optical emission spectrometry with charge coupled device detection (ICP-OES-CCD). The removal of calcium, potassium, manganese, and copper from glasses designed to simulate medieval stained glass has been assessed to investigate the effect of (a) EDTA concentration and (b) the pH of the EDTA cleaning solution. The extent of removal of the constituent elements appears to be more dependent on the pH than on the concentratoin of EDTA; eg. the leaching of calcium is greater at pH 7.5 than at pH 6.5. The resultant damage to the glass surfaces has been studied by scanning electron microscopy. In complementary experiments the efficacy of EDTA as a cleaning reagent has been assessed through its efficiency at dissolving a typical weathering product (CaSO4). Again, the parameters of interest were the EDTA concentration and the pH of the solution. The aim of the study is to identify conditions that are effective in removing weathering products, but with minimal damage to its glass surface.