Copper Panel Paintings

The Conservation of a Chancel Scheme

Michael Bowes

 

  The painting of the 'Jesus in the Temple' from the south east niche after conservation  
  The painting of the 'Jesus in the Temple' from the south east niche after conservation, showing the almost three-dimensional quality of the gilded and painted surfaces. (All photos: Michael Bowes)  

In the late 19th century, artists and craftspeople experimented with many different types of decoration to bring colour and opulence into the ecclesiastical interior. One of the most striking is a form of panel painting seen around the chancel of St Mary the Virgin, the parish church of Bury in Greater Manchester.

The church was designed by architect J S Crowther and was consecrated in 1876, and the panel paintings were installed 12 years later, but the artist is unknown. The scheme consists of four scenes from the life of the Blessed Virgin set within blind arcading on either side of the altar. These are the Annunciation, the Nativity, Temple Scene and the Adoration of the Magi. The compositions include brightly coloured figures and stylised architectural elements picked out in gold leaf to dramatic effect.

Over a century later the surfaces had become worn and disfigured, so a programme of conservation was undertaken to consolidate the fabric and to consider options for their repair and restoration.

FORM AND CONSTRUCTION

On inspection it was discovered that each panel is made up of between eight and 13 separate metal plates attached to the masonry of the chancel wall and small traces of a green corrosion product at the edges indicated that the metal is copper. The attachments are in two forms: brass bolts with decorative heads at the edges of the plates and flat head screws, filled and painted to match the detail within the plates.

This choice of material may seem unusual, but copper sheet has been widely used as a support for panel painting for two main reasons. Firstly, its durability ensures that the paint remains generally free from the characteristic cracking seen in paintings executed on more traditional supports such as canvas or wood. Secondly its smooth, rigid surface allows the paint to be manipulated easily, enabling extremely fine detail to be achieved. Furthermore, the surface is non-absorbent so the paint does not sink in and become matt. This means that oil paintings on copper often retain a high degree of saturation and hue, lending a vibrant, jewel like appearance to the surface (Horovitz 2017 – see further information).

The preparation of copper for painting is well described in several historical records (Horovitz 2017). In some cases paint would have been applied direct to the copper panel, allowing the artist to work from a darker red or orange colour to create certain visual effects such as a warm hue to the skin tones. However, most include a thin layer of lead white and drying oil as a ground layer. It is this technique that seems to have been used across the entire surface of the chancel panels, as brushstrokes could be observed to pass consistently under the areas of gold and thin upper paint layer.

The painted areas were executed in oil paints using a wide variety of pigment types including a range of earth colours (umber, ochre, sienna), rich reds including alizarin crimson and vermilion, greens including viridian, oxide of chromium and possibly malachite, lead white, and several yellows. The gold areas were oil-gilded (gold leaf on an oil-based size) resulting in a smooth continuous surface of pure gold, both as a backdrop to the figures and to enrich the architectural elements of the scheme.

HISTORIC BACKGROUND

  The St Mary the Virgin parish church chancel decoration includes oil on copper panels in niches, a reredos designed by J Harold Gibbons of Westminster and constructed by Boulton and Sons of Cheltenham and Minton floor tiles.  
  The chancel decoration includes oil on copper panels in niches, a reredos designed by J Harold Gibbons of Westminster and constructed by Boulton and Sons of Cheltenham and Minton floor tiles.  

The use of copper as a support for painting was by no means a new concept. The art writer Vasari records that in the early 16th century Italian artists were experimenting with various unusual supports such as stone, marble and porphyry in search of novel ways to extend the life of the artwork and to produce specific paint effects. In Florence the practice of painting on stone as well as several types of metal, including copper, was actively encouraged by the wealthy patrons of the period. Slate was particularly popular for dark paintings or night scenes in which its grey colour was used to establish the shadow tones of the painting.

Despite its popularity, stone had the disadvantage that it was relatively heavy and when thinner lighter sections were used, there was a high risk of breakage. It was here that copper gained its advantage. Providing both a pristine flat surface on which to paint and a durable support for the artwork, its comparative light weight made it an excellent choice.

Until the 18th century almost all copper painting supports were produced by hammering ingots of copper in order to adjust the thickness and shape. There are limited records of small rolling mills existing in the 17th century, some powered by water mills, but these were used for small scale fine adjustment of the sheet rather than larger alterations. The use of larger industrial rolling mills only became widespread during the late 18th century when copper was used for covering domes or roofs of churches and palaces and for the protection of ships’ hulls (Vega 2016).

For painting and gilding, the copper plate is finished in much the same way as a plate used in etching, and it is not polished to a high degree. The surface may even be roughened to provide a tooth for the paint to adhere.

Copper has several properties which make it suitable for painting, particularly in a church environment. Its low coefficient of thermal expansion means that it expands and contracts very little in response to temperature changes, and unlike timber it does not move in response to changes in humidity. This contributes greatly to the longevity of the paint layer and accounts for the absence of cracking.

The metal is also comparatively resistant to corrosion. Extremes in temperature and relative humidity above 65 per cent can allow moisture ingress through micro cracking in the paint and ground layers, and in some situations this can lead to corrosion. However, copper usually develops a red coloured patina of cuprous oxide (Cu2O) which forms a protective layer and prevents further corrosion in stable environments.

As well as being painted, there are historic examples of copper plates having a silvered surface composed of tin or lead-tin alloys, or a highly gilded surface applied on top of lead and oil ground (Horovitz 2017). It is this latter combination which was used most effectively at Bury.

CONDITION OF THE PANELS

  Opaque white blanching of the varnish obscured significant areas of the oil on copper painitings
  Before conservation: opaque white blanching of the varnish obscured significant areas of the oil on copper paintings.

The conservation project was undertaken by the team at David Everingham Conservation Ltd, a Harrogatebased studio which specialises in the conservation of easel paintings. The scheme was examined and analysed when concern was raised about the abraded appearance of the gilded background of the panel depicting the Adoration of the Magi. Close inspection revealed several other significant issues. The scheme was covered with a layer of surface dirt probably caused by candle burning and high city pollution levels, and tests and visual examinations revealed an underlying varnish layer which was yellowing and profoundly degraded. This form of degradation is typically caused by oxidising agents in the atmosphere and the effects of daylight (ultraviolet radiation). Over many years this alters the bonding of the molecules within the varnish, leading to colour change and crosslinking of the molecular structure. An unfortunate side-effect of this ageing process is a shift in the solubility parameters, making the varnish difficult to remove without harming the underlying paint layers.

There were also many areas of blanching within the varnish layer. This appears as a white cast, often translucent, but sometimes almost opaque, obscuring the image completely. This generally occurs when the varnish has been affected by solvent action, perhaps spillages or cleaning, or in some cases atmospheric action upon the varnish.

Additionally, the paintings exhibited many scratches and abrasions, very limited corrosion of the copper panels at the edge, and several instances where the original gilded surfaces were damaged. The abrasion to the oil gilded sections appeared to have been caused in part by years of dusting which gradually wore down the thin gold leaf and exposed the ground layer.

Fortunately, the copper substrate itself was generally in very good condition. The traces of green copper salt staining found on the wall were limited, and the back of the plates exhibited the red and orange colour that is indicative of a stable patina.

Based upon these investigations and the detailed conservation condition report, the decision was made to undertake a comprehensive conservation programme to the decorated surface only, to prevent further loss of decoration and to ensure its longevity. It was decided to use this opportunity to repair areas of damage at the same time.

CONSERVING THE PANELS

The programme of conservation included removing the surface deposits and the discoloured varnish, re-gilding areas of abrasion and toning to match the aged gilding, retouching damaged surfaces and re-varnishing with a conservation grade, age tested varnish.

Although cleaning is one of the most irreversible treatments that conservators embark upon, it is usually deemed to be a necessary part of most conservation programmes. In this instance the surface dirt and varnish were contributing to an overall darkening of the images and a shift in hue and tone of the applied colours.

  An angel from the Adoration of the Magi, partly cleaned to show the discolouration caused by the layer of surface dust and dirt, and the yellowing varnish layer.  
  An angel from the Adoration of the Magi, partly cleaned to show the discolouration caused by the layer of surface dust and dirt, and the yellowing varnish layer.  

Part of the assessment responsibility is to adhere to conservation principles and consider the artistic intentions, purpose and context of the artworks. Considering the importance of colour in the chancel paintings and the need for clarity of form in depicting the scenes, the decision was taken to remove both the surface dirt and varnish to reveal the colours originally intended. During the testing phase and the ‘unpacking’ of the layers it was found that the accumulated dust and pollutants on the surface could be successfully separated from the varnish layer and removed using aqueous cleaning methods, and that a formulated solvent-based method could be used to gradually remove the degraded varnish. The removal method was based on a swab application of propanone placed within a gel formulation (using Ethomeen and Carbopol, the process developed by Richard Wolbers to help maintain contact between the solvent and the surface, while minimising evaporation). In this case the gel was applied by swab and rolled on to the surface as if it were a free liquid solvent. The discolouration on the swab was monitored during cleaning and the gel was then removed from the surface with a clean cotton swab and water. This method proved to be both effective and safe, enabling the discoloured varnish to be separated from the paint layer.

The abraded sections of the original gold were re-applied using oil size and 24 carat gold leaf. The colour disparity between the new and aged gold was corrected by the application of toned transparent glazes over the new applied gold. These glazes were mixed using pigments bound in Paraloid B72 resin.

All the materials and techniques were selected according to our guiding conservation principles with the longtermvitality of the panels in mind. Two of the most important ethics, the reversibility of treatments, and adhering as far as possible to the original intentions of the artist, were observed at all times.

The photographs are testimony to the dramatic improvement in the appearance of the panels. Dull greys turned into brilliant whites, browns into rich reds and the gilded surfaces reflected light with the brilliance of freshly applied gold leaf.

Further Reading

I Horovitz, “Paintings on copper: a brief overview of their conception, creation and conservation”, Proceedings from the symposium, Paintings on copper: and other metal plates: production, degradation and conservation issues, 17–26, València, 2017

L Pavlopoulou, 'Chemical, physical and mechanical decay processes in oil painted copper objects', Proceedings from the symposium, Paintings on copper: and other metal plates: production, degradation and conservation issues, 43–54, València 2017

D Everingham, 'The characterisation, origin and treatment of ‘surface eruptions’ on a seventeenth century oil on copper', MA Dissertation, University of Northumbria, 1998

Phoenix Art Museum, Nelson-Atkins Museum of Art, and Mauritshuis (Hague, Netherlands), Copper as canvas: two centuries of masterpiece paintings on copper, 1575–1775. New York: Oxford University Press, 1999

Historic Churches 2018

Author

MICHAEL BOWES (michaelbowes99@gmail.com) studied for his MA Conservation of Fine Art at Northumbria University. After working at The Bowes Museum in County Durham and a short internship at the V&A Museum he is now assistant paintings conservator at David Everingham Conservation Ltd in Harrogate, North Yorkshire.

 

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