Stephen Hackney

THE BENEFITS AND RISKS OF ANOXIC DISPLAY FOR COLORANTS

Abstract Tate is undertaking a major research project to assess the effects of anoxic storage on paper-based works of art. The outcomes will include: the design of a safe, affordable anoxic framing system suitable for both storage and display, capable of being incorporated into historic frames; guidelines on materials which would be harmed by anoxia and information on their recognition and behaviour. Such framing would provide safer access to paper-based works of art. This paper reviews the following materials found in paper-based works of art that are susceptible to oxidation and which could therefore benefit from anoxia: traditional colorants; modern pigments; graphic media; printing, copying or photographic processes; and oil or alkyd media. Materials, predominantly colorants, which may be susceptible to reducing reactions that proceed in the absence of oxygen, are identified for later study into their behaviour and their non-destructive identification on paper-based works of art.

Framing for conservation at the Tate gallery

A discussion on the history of framing at the Tate Gallery and on the actual framing policy which has re-established the glazing of selected works. Considerations are made of the microclimate and the problem of humidity, the glazing of the backboards, the microenvironment, the external and internal pollution.

Evaluation of the effects of environmental conditions and preventive conservation treatment on painting canvases

Abstract The use of preventive conservation measures to assist in retarding the deterioration of painting canvases has been suggested by the Conservation Department of the Tate Gallery [S. Hackney and T. Ernst, The applicability of alkaline reserves to painting canvases, in Preventive Conservation Practice, Theory and Research, Pre-prints of the contributions to the Ottawa Congress, 12–16 September 1994, Ottawa, Canada, p. 223–227]. The reverse sides of paintings are treated with commercially available methoxy magnesium methyl carbonate (MMC) solution. The aim of this paper is to describe how dynamic mechanical thermal analysis can be used to evaluate the effects of this treatment. Measurements are described on modern commercially primed canvas samples [N. Wyplosz, S. Hackney and J.H. Townsend, Studies on the deacidification of canvas with methoxy magnesium carbonate (MMC), in pre-prints of the European Commission research workshop “Effects of the Environment on Indoor Cultural Property”, p. 30.] which show that the MMC treatment does affect the mechanical properties of the treated canvas samples and that dynamic mechanical thermal analysis (DMTA) is a suitable technique for its evaluation. The treatment appears to produce a coating on the samples which acts as a moisture barrier. This was also found to occur for treated historic samples (Battelle process) from loose-lining canvases removed from 19th century paintings. The response of the MMC treated materials to variations in relative humidity has also been studied and indications are that their response to variations in relative humidity differs from those of the untreated canvases.

Photochemical colour change for traditional watercolour pigments in low oxygen levels

Abstract An investigation for light exposure on pigments in low-oxygen environments (in the range 0–5% oxygen) was conducted using a purpose-built automated microfadometer for a large sample set including multiple samples of traditional watercolour pigments from nineteenth-century and twentieth-century sources, selected for concerns over their stability in anoxia. The pigments were prepared for usage in watercolour painting: ground and mixed in gum Arabic and applied to historically accurate gelatine glue-sized cotton and linen-based papers. Anoxia benefited many colorants and no colorant fared worse in anoxia than in air, with the exception of Prussian blue and Prussian green (which contains Prussian blue). A Prussian blue sampled from the studio materials of J.M.W. Turner (1775 − 1851) was microfaded in different environments (normal air (20.9% oxygen) 0, 1, 2, 3.5, or 5% oxygen in nitrogen) and the subsequent dark behaviour was measured. The behaviour of the sample (in normal air, anoxia, and 5% oxygen in nitrogen) proved to be consistent with the 55 separately sourced Prussian blue samples. When exposed to light in 5% oxygen in nitrogen, Prussian blue demonstrated the same light stability as in air (at approximately 21°C and 1 atmosphere). Storage in 5% oxygen is proposed for ‘anoxic’ display of paper-based artworks that might contain Prussian blue, to protect this material while reducing light-induced damage to other components of a watercolour, including organic colorants and the paper support.

DYNAMIC MECHANICAL THERMAL ANALYSIS FOR THE EVALUATION OF DEACIDIFICATION TREATMENT OF PAINTING CANVASES

The use of non-aqueous deacidification procedures as a preventive conservation measure to assist in retarding the deterioration of painting canvases has been suggested by the Conservation Department of the Tate Gallery [1]. The reverse sides of paintings are treated with commercially available MMC solution (methoxy magnesium methyl carbonate). The aim of this paper is to describe how dynamic mechanical thermal analysis can be used to evaluate the effects of this treatment. Measurements are described on modern commercially primed canvas samples [2] which show that the MMC treatment does cause an increase in the modulus or stiffness of the primed canvas materials but that the effect on theTg is minimal. The response of the treated materials to variations in relative humidity has also been studied and indications are that the response of treated canvases to variations in relative humidity differs from those of the untreated canvases.

A Versatile Microfadometer for Lightfastness Testing and Pigment Identification

The design and experimental method for the use of a novel instrument for lightfastness measurements on artwork is presented. The new microfadometer design offers increased durability and portability over the previous, published design, broadening the scope of locations at which data can be acquired. This reduces the need for art handling or transportation in order to gain evidence-based risk assessments for the display of light-sensitive artworks. The instrument focuses a stabilized high powered xenon lamp to a spot 0.25 millimeters (FWHM) while simultaneously monitoring color change. This makes it possible to identify pigments and determine the lightfastness of materials effectively and non-destructively. With 2.59mW or 0.82 lumens (1.7 x107 lux for a 0.25mm focused spot) the instrument is capable of fading Blue Wool 1 to a measured 11 ΔEab value (using CIE standard illuminant D65) in 15 minutes. The temperature increase created by focused radiation was measured to be 3 to 4°C above room temperature. The system was stable within 0.12 ΔEab over 1 hour and 0.31 ΔEab over 7 hours. A safety evaluation of the technique is discussed which concludes that some caution should be employed when fading smooth, uniform areas of artworks. The instrument can also incorporate a linear variable filter. This enables the researcher to identify the active wavebands that cause certain degradation reactions and determine the degree of wavelength dependence of fading. Some preliminary results of fading experiments on Prussian blue samples from the paint box of J. M. W Turner (1755-1851) are presented.

Assessment of indoor air quality and the risk of damage to cultural heritage objects using MEMORI® dosimetry

Air pollution is one of the environmental influences that degrade cultural heritage objects situated indoors. Other essential influences, such as temperature, relative humidity, and light are often well monitored. The presence of air pollutants is less often measured or included in risk assessment. The MEMORI® technology presented in this paper was developed as a tool for easy measurement and assessment of the general risk of degradation of heritage objects situated indoors due to indoor exposure to air pollutants. MEMORI dosimetry was performed in locations belonging to English Heritage and Tate (both located in London) and the National Archives of Norway in Oslo, to assess air quality. The related damage risk for collection objects and the protection offered by display and storage designs was assessed. A high level of acidic effect was observed inside a number of showcases, and a high level of oxidizing effect was observed in some room locations. Relatively simple mitigation measures, such as constructing tightly sealed showcases using low emitting materials, installing active carbon absorbing media inside a ‘microclimate’ frame, and using cardboard storage boxes for paper, significantly improved air quality. Overall, implementation of such measures is likely to improve the preservation of objects and reduce conservation costs.

Paint and Purpose: A Study of Technique in British Art

Recent advances in scientific analysis are used to shed light on the working practices of artists of all periods. Revealed in this book are 30 intriguing case histories, including those of many notable British artists, all the results of study by conservators and scientists at the Tate Gallery.