The following are common issues which may arise in paintings and the approaches that are used to treat these problems (also see Anatomy of a Painting for painting component definitions):
Flaking, cleavage, tenting, powdering, interlayer separation, bond failure
These are all terms which indicate a loss of cohesion or adhesion, which eventually leads to loss of paint from the support layer. The nature and cause must be determined by the conservator in order to effectively address the problem through some form of consolidation treatment. Typically the paint is softened (usually with moisture) before a consolidant is introduced so that the lifted paint may be lain down without causing further cracking and fragmentation.
Not all cracks are created equal, or rather, not all cracks look the same because the mechanism of their formation varies. Different kinds of cracks include “alligator” or traction cracks, cracks due to impact or pressure (spiral, concentric, feather), ageing cracks (craquelure), “cupped” cracks. Cracks may simply indicate the painting’s age and are generally not treated unless they are associated with instability in the paint layer, which could lead to paint loss, or are so unsightly that the image is difficult to view. Some of the “traction” cracks in the above barnyard scene were retouched where the cracks were so wide and concentrated that the image appeared fragmented and difficult to read.
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; instead, the torn yarns are gradually sorted, aligned, and re-woven in place. The work can only be undertaken using specialized micro-tools while viewing the area through a binocular microscope.
A painting may be coated with one or more layers or types of varnish (made from natural or synthetic resins) or some other kind of surface coating. Some coating materials discolour and the discolouration may be severe, particularly if a thick application is present. Light and cool colours appear especially altered when seen through a yellowed haze. The coating is identified as to type and extensive removal tests undertaken by the conservator before proposing removal, should removal be deemed desireable.
Dirt and Accretions
The above work, purchased in a church bazaar, was probably donated due to its poor condition – the brown drip marks covering the surface of the painting and the frame ran from the left to the right side leaving the horizontal marks shown above (simply indicating that the work was in a sideways orientation when a discoloured liquid ran down the surface). The drip marks were water-soluble and the work’s original appearance was recovered through surface cleaning.
Surface cleaning is probably the most common treatment undertaken by paintings conservators. Like varnish removal or any other treatment, it must only be undertaken by a paintings conservator. The characteristics of the painting and that of the surface dirt and deposits must be determined in order to design a safe and effective method of removal. As an example, I once saw a painted miniature on ivory destroyed in one second after the owner ran a damp cloth over its surface, not understanding that the paint medium was water-soluble. This process is much more complicated than is sometimes imagined. There is no safe, one-type fits all, off-the-shelf picture cleaning solution (even though such a thing has been available commercially, next to the snake oil).
Years ago I wrote a conservation brief for the Alberta Museums Association titled: “Why You Should Not Clean Your Masterpiece (or Any Other Painting)! As I wrote then, people sometimes attempt to clean paintings themselves because they consider them to be of too little value to warrant professional treatment. The risk of damage being done is great and usually irreparable. Value and the perception of value of a painting changes over time and from generation to generation.
Canvas deformations, warpage of rigid supports
When the primary support is no longer flat and in plane, paint flaking and loss may occur. As oil paint ages, it becomes more brittle and less able to accommodate movement and out-of-plane distortions in the support. Some movement occurs in all the layers of painting as relative humidity changes; different materials/layers respond differently creating stress. Limiting RH changes and the painting’s dimensional response to these changes is therefore desireable, either through modification of the HVAC system and/or buffering of the painting within a protective framing envelope or micro-environment.
This ancestral portrait was technically unusual, consisting of oil on two layers of paper with a fabric backing, put on a wood stretcher to simulate the appearance of a canvas painting. The fabric backing was degraded and required removal, which also allowed access to the tears in the paper support layers.