Abstract
Two Burmese oil paintings on zinc supports depicting portraits of royal families, dated to the early 20th century by Saya Aye and Saya Mya, showed interesting corrosion, efflorescence and soapy globules for analytical investigation prior to conservation for exhibition. The features and colours on the two paintings, one of which was in worse condition than the other, were obscured by a whitish haze. Paint rupture and losses due to corrosion of the zinc support were apparent. Using a combination of 3D digital microscopy, FTIR microscopy and SEM–EDS, the degradation, as well as the paint materials and artists’ techniques were analysed and discussed. Zinc soaps, oxalates, silicates, hydroxychlorides, carbonates, wax and mould characterized the haze. Interestingly, brown outlines in Aye’s painting appeared unusually dark. Upon analysis, this degradation phenomenon was attributed to micro-sized greenish soap globules that have developed around copper/zinc (brass) particles, causing the brown outlines to lose their intended luminosity. The other painting by Mya, in which the same brown outline was applied, did not show such formation of globules. Detection of oxalates in the corrosion of zinc support and brown outlines are discussed. This study shows the importance in understanding the artists’ materials and techniques, which have consequential effects to the degradation observed.
Highlights
The use of metal support for paintings, most commonly copper, has been favored by artists since ancient times for their reflected luminosity, durability and resistance to fluctuations in relative humidity [1]
Copper soaps forming at the oil-copper interface have been hypothesized to contribute to the delamination of paint [2] and corrosion of the metal substrate could lead to paint blistering [3]
This paper presents a case study that investigates the degradation on two Burmese oil paintings on zinc supports (c. 1918), “Royal Family Portrait with Musician” by Saya Aye (1872–1930) and “Royal Family Portrait” by Saya Mya (1893–1979), recently acquired into the collection of the National Gallery Singapore (Fig. 1a, b)
Summary
The use of metal support for paintings, most commonly copper, has been favored by artists since ancient times for their reflected luminosity, durability and resistance to fluctuations in relative humidity [1]. Not all paintings on metal support could survive without problems. Copper soaps forming at the oil-copper interface have been hypothesized to contribute to the delamination of paint [2] and corrosion of the metal substrate could lead to paint blistering [3]. Only one publication was identified on the conservation of painted zinc supports as part of the rebuilding of the Church of St David in Little. The zinc cations formed on the surface of zinc metal can potentially react with fatty acids released from the hydrolysis of oil binder, giving rise to zinc soaps at the paint-metal interface [8]. Zinc soaps accumulating at the paint-ground interface can contribute to paint embrittlement and delamination problems [9,10,11,12]
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