This post describes some common issues that may arise in paintings and treatment approaches that may be used to correct them.
Flaking, Cleavage, Tenting, Powdering, Interlayer Separation, Bond Failure
These are all terms that describe loss of cohesion or adhesion that may lead to paint loss. The nature and cause must be determined by the conservator in order to effectively address the problem through consolidation treatment. Typically the paint is softened (usually with moisture) before a consolidant is carefully introduced at the correct interface.
Detail showing severe interlayer separation on a polychrome sculpture.
Not all cracks are created equal, or rather, not all cracks look the same because the mechanism of their formation varies. Different types of cracks include “alligator” or traction cracks, cracks due to impact or pressure (spiral, concentric, feather), ageing cracks (craquelure), “cupped” cracks where the paint lifts upward at the crack edges. Cracks do not necessarily require treatment unless there is associated instability.
Rather severe and numerous traction cracks are shown in this charming barnyard scene by Danish-Canadian artist Theodore Jensen. Some of the traction cracks were retouched where their width and concentration resulted in visual fragmentation. The viewer’s ability to read a cohesive image is taken into account.
Paintings on canvas are vulnerable to being torn, particularly when a protective, rigid backing board has not been installed. The tear repair process is one of the most time-consuming treatments in paintings conservation. Torn paintings are not patched as was once done. The torn yarns are gradually re-woven and the ends re-joined using specialized micro-tools while viewing the area through a binocular microscope.
The reverse of a severe tear is shown here during repair; the outer ends of the tear have already been rewoven and secured as per a German “thread-by-thread” technique refined by Winfried Heiber.
The way a canvas tears depends on many factors including the nature and magnitude of applied force, and the strength and type of the canvas. In turn, cracks and paint losses may be limited or, as shown here, may radiate well beyond the tear line.
The torn painting after tear repair and filling and inpainting of losses.
Deformations of the primary (image-bearing) support
If the primary support is not planar, paint flaking and loss may occur. As oil paint ages, it becomes more brittle and less able to accommodate movement and distortions in the support. The physical properties of each material layer varies with changes of temperature and relative humidity (RH). Since each layer responds differently, stress occurs and damage may result.
This painting was forced into a picture frame, deforming the canvas and causing the paint to crack and separate as shown in the corner detail above.
When a protective backing is not present, debris accumulates behind the bottom stretcher bar that may deform the canvas outward and cause paint loss. Dust, lint, plaster fragments, nails, plant matter, stretcher keys, and insect debris are common components of this near-archaeological build-up. Particularly heavy accumulations were revealed during temporary separation of the stretcher from the oval canvas shown. The debris may provide telling evidence of the display or storage environment.
A yellowed varnish layer distorts the viewer’s perception of paint colour. Light and cool colours such as white and blue of sky and water appear especially altered when seen through a yellowed film. Before removal is considered, the varnish must be characterized as to composition, solubility and overall condition.
“Near Gang Ranch” by Peter Ewart
Dirt and Accretions
The safe removal of dirt and accretions requires the same degree of analysis, judgement and expertise as other treatments. Cleaning should only be undertaken by a qualified paintings conservator or permanent damage may occur in an instant.
Market value and the perceived value of a painting is transitory. A thrift store find or family heirloom may prove more valuable than is apparent at first sight, as in this Canadian news story.