Every potential conservation treatment and every technical study of a particular painting begins with a thorough visual examination of the artwork. Technical photography is a useful non-invasive tool for conservators. Many artists' materials exhibit ultra-violet (UV) fluorescence: that is, they emit visible light when illuminated with ultra-violet light. The human eye cannot detect UV but some materials absorb it and then emit it as visible light. The above image shows a detail of The Marriage of Strongbow and Aoife before cleaning, where the uneven varnish fluoresces a milky green colour whilst old restorations appear black as they block underlying surface-layers. This technical analysis enables conservators to gain an understanding of the type of a varnish layer present and can also help detect old restorations.
On ageing, varnish may become very yellow. This type of discolouration will alter the tonal balance within the painting, making it look significantly different from how the artist intended. This may necessitate the removal of the varnish layer, and replacement with a new varnish layer that has better ageing properties.
Varnish removal is usually achieved with the use of solvents, such as alcohols, ketones and hydrocarbons. However, the use of solvents on a paint surface carries many dangers. Soluble components may be leached out of the paint film when solvents are applied to the surface. Solvents also have a significant swelling effect on paint. Some paint surfaces may be sensitive to solvents and will dissolve, pigments can vary in their sensitivity to solvents whilst degraded oil paint may also be affected by solvent based cleaning processes.
Cleaning tests using low aromatic polar solvents were undertaken on The Marriage of Strongbow and Aoife to remove layers of accumulated dirt and varnish from the paint-layer. An appropriate and safe cleaning methodology was then devised for the cleaning of the painting. Removal of the varnish is a complicated and long process, however treatment to date has achieved very positive results, revealing the beautiful detail of Maclise’s brushwork.
Some of the old labels and patches on the reverse of the stretcher were treated by the Gallery’s paper Conservators. Find out more.