Historic Churches 2018

30 BCD SPECIAL REPORT ON HISTORIC CHURCHES 25 TH ANNUAL EDITION HISTORIC BACKGROUND 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 (Cu ₂ O) 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 The conservation project was undertaken by the team at David Everingham Conservation Ltd, a Harrogate- based 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. 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.