A network of cracks, a whitish haze, a dent in the canvas or a few missing flakes of paint can reveal a great deal about the condition of a painting. To recognise damage, however, it is first necessary to understand how a painting is constructed, which changes are part of natural ageing, and which signs may indicate genuine instability.
On an old painting, the paint surface may appear completely covered with fine cracks when viewed up close. They become particularly visible in raking light: straight lines, small islands and, in some cases, an almost regular network extending across large areas of the surface. The immediate question is understandable: is the paint cracking and therefore damaged? Not necessarily.
Craquelure is one of the clearest examples of the difference between visible ageing and active deterioration. Cracking forms part of the material history of many paintings. The condition becomes more concerning when the edges of those cracks begin to lift, paint flakes become loose, areas of paint are lost, or the pattern can be shown to be changing.[1]
A painting is made up of layers
A traditional painting on canvas generally consists of a woven support stretched over a stretcher or strainer, followed by a preparatory ground, one or more paint layers and, in many cases, a varnish. A panel painting has a rigid support made from wood or another material, but here too the ground, paint and any surface coatings lie one above another.[1]
These materials do not all behave in the same way. Wood responds differently to moisture than paint does. Canvas can slacken, shrink or deform. Glue-containing grounds can react strongly to changes in climate. An old oil-paint layer becomes less flexible with age. Varnish may discolour or become brittle.
A raised paint flake, for example, may be associated with a loss of adhesion between the paint and the ground, but also between the ground and the canvas. A crack pattern may be related to long-term ageing, the original painting technique, fluctuations in relative humidity or mechanical stress such as an impact to the canvas.[1]
Craquelure is not automatically a condition problem
Craquelure is a network of cracks in paint or varnish layers that can develop as a result of ageing, technical properties of the materials and movement between the various layers and the support. Such crack networks are extremely common in older paintings.[1] Importantly, not all craquelure has the same origin.
Age-related craquelure develops during the material life of a painting as stresses and changes occur within its different layers. Primary or drying craquelure, by contrast, may have developed relatively early, while the paint was drying, for example because of the particular build-up or composition of different paint layers. Mechanical cracks may also occur as a result of pressure, impact or deformation.[1]
A certain degree of cracking in ground and paint layers is unavoidable in many older paintings and does not automatically mean that the work is unstable. The situation changes when individual paint islands begin to curl upwards along the cracks or develop shallow, cup-like forms. Such cupped or lifting edges are more vulnerable to flaking and paint loss.[1]
When loose paint really is a warning sign
The situation is different when paint is genuinely loose. Conservators use several terms to describe different forms of separation between layers. Cleavage refers to separation between layers. With lifting, paint rises locally from the surface. With cupping, areas of paint bordered by craquelure develop raised, cup-shaped edges. With flaking, fragments of paint or ground have become partially or completely detached from the layer beneath.[1]
A tear or hole in the canvas: size alone tells us little
A tear in a painting on canvas is a different kind of problem. Here, it is not only the paint layer that is affected: the primary support itself has been disrupted. A relatively short, recent tear may involve distorted fibres and loose paint along its edges. A much longer, older tear may have been professionally repaired in the past and may now be stable.
Assessment should therefore take into account the position of the tear, the deformation of the canvas, the condition of the fibres and, above all, the condition of the ground and paint surrounding the damaged area. Tears in canvas should not be left untreated unnecessarily. As damaged threads move further out of alignment, later reconstruction may become more difficult.[2]
Bulges, dents and distortions in canvas
A canvas does not have to be torn to become structurally deformed. A dent is an inward deformation, usually caused by impact or pressure. A bulge projects outward. Such distortions can occur following an impact from the reverse, prolonged pressure, or because an object has become trapped between the canvas and the stretcher, such as debris or a loose component.[1]
Wavy distortions and so-called corner draws can also develop along edges and corners. Climate and uneven tension can play a role. This can easily prompt an incorrect do-it-yourself response: the canvas appears slack, so the wooden keys in the corners of the stretcher are driven further out to make the surface tighter. In fact, this can cause additional damage.
Keying out is not a general solution for a slack or distorted historic canvas. Increasing the tension can create new cracks in a brittle ground and paint layer and aggravate existing problems.[2] A bulge therefore does not automatically mean that “the canvas needs to be restretched”. The cause of the deformation must first be established.
Water damage can affect several layers at once
Water is one of the circumstances in which more rapid action may be justified. In a painting on canvas, moisture can alter the textile support and cause the stretcher to swell or deform. Grounds and paint layers may swell, detach, crack or flake. Paint and varnish layers may develop a local whitish haze. In panel paintings, the wooden support may swell or warp. If a painting remains damp for an extended period, the risk of mould growth also increases.[3]
A white haze is not a diagnosis
A milky or whitish veil on a painting is often described as “water damage”. That conclusion may be premature. Conservators use terms such as blanching and bloom for different whitish surface phenomena. Moisture can indeed cause blanching in paint or varnish.
Visually similar effects may, however, also result from a matte varnish, surface contamination, old restoration materials or other changes to the surface. Without further examination, a “white haze” should therefore be treated as an observation rather than a material diagnosis.
Why does an old painting become dark?
A dark painting is often explained simply by saying that “the varnish has yellowed”. Old surface deposits may include dust, grease, soot, cooking residues and tobacco smoke. Many traditional varnishes discolour and darken as they age. Old retouching may age differently from the original paint. Past cleaning may have abraded parts of the surface. Some original pigments and binding media can also undergo chemical changes of their own.
A dark surface therefore does not tell us how a painting will look after conservation treatment. That can only be assessed through material examination and carefully controlled cleaning tests. This is also why cleaning a painting yourself is risky. What appears to be dirt may lie over a sensitive or already compromised paint layer, and a cleaning agent capable of removing one layer may also affect original material.[4]
When should a conservator examine the painting?
Not every old crack requires treatment. Professional examination is advisable when paint is visibly lifting or becoming detached; when new paint losses appear; when a tear or hole has occurred recently; when the canvas is severely distorted; following direct water exposure; or when mould is suspected. The essential question is therefore not whether a painting shows signs of age. Historic paintings almost invariably do.
A dense network of flat craquelure may have formed part of a painting’s condition for a very long time. A barely visible raised paint flake, by contrast, may require immediate attention. Understanding that distinction means looking not at every irregularity as damage, but at the layer involved, the likely cause, the degree of adhesion and whether the condition is changing.
Notes and sources
[1] Rijksdienst voor het Cultureel Erfgoed, “craquelure”, “ouderdomscraquelure” and “primaire craquelure”, Cultuurhistorische Thesaurus; Canadian Conservation Institute, Know Your Paintings – Structure, Materials and Aspects of Deterioration; Canadian Conservation Institute, Condition Reporting – Paintings. Part III: Glossary.
[2] Canadian Conservation Institute, Basic Care – Paintings, including guidance on torn canvas, treatment, climate, handling and repair; Canadian Conservation Institute, Keying Out of Paintings.
[3] Barbara Klempan / Canadian Conservation Institute Fine Arts Section, Emergency Treatment of Water-damaged Paintings on Canvas; Canadian Conservation Institute, Environmental Guidelines for Paintings.
[4] Canadian Conservation Institute, Cleaning Paintings: Precautions.