Paintings

What are the most common types and causes of damage?

As with most cultural material, the deterioration of paintings is caused by physical damage and chemical activity—usually in combination.

Physical damage is very obvious and includes:

Tears and breaks. For example, many canvas paintings are damaged when people are working near the paintings and accidentally put the handle of a broom, a ladder etc. through the canvas. This is not uncommon.

This pre-treatment photograph shows severe tears in the canvas support of a painting. Photograph courtesy Artlab Australia

Cracking of varnish and paint layers because of movement of the support, due to:

• vibration during handling and travel;

• impact when a painting is dropped, knocked or falls off a wall; and

• fluctuations in relative humidity. Both canvas and wood take up and release moisture as the relative humidity fluctuates. This produces dimensional changes which can lead to cracking of the paint and varnish.

Separation of the different layers of the painting structure. This can because by fluctuations in relative humidity and/or to impact.

Softening of the varnish layer in high temperatures. The varnish can become sticky and any dust or dirt on the surface may become permanently attached to the painting.

Warping of the stretcher due to extremes and fluctuations in relative humidity, and lack of proper support in storage or display.

Insect attack, for example, wooden stretchers can be attacked by borers and canvas and cardboard supports can be attacked by silverfish.

This stretcher had been exposed to quite extreme fluctuations in relative humidity causing it to warp severely. In time, this resulted in the structural breakdown of the stretcher with obvious damage to the canvas support. Photograph courtesy Artlab Australia

Dust and dirt can distort paintings if allowed to collect between the lower stretcher bar and the canvas. This can lead to distortion of the paint layer. Dust will also take up and hold moisture, thus creating a localised area of high humidity—this can lead to localised dimensional change and overall distortion.

Chemical deterioration can be very damaging and will often mar the appearance of paintings. Chemical damage to paintings includes:

Colour change and fading of pigments when exposed to light and UV radiation. Oil paintings are often considered to be quite stable in light, but some pigments and glazes are particularly susceptible to light damage.

Discolouration of the varnish. This may be due to exposure to light and UV radiation and/or because of the natural ageing of the particular varnish.

This photograph taken during treatment shows clearly the degree to which varnish can discolour and alter the appearance of a painting. Photograph courtesy Artlab Australia, reproduced with permission of Mr Paul Fitzgerald

Deterioration of some components of the painting where poor-quality materials have been used or where the painting has not been properly structured.

Reactions between incompatible components of the painting. This is more likely to occur when the painting is a complex collage made up of a combination of paint and a number of other materials.

Cracking or movement of paint layers due to the unstable nature of one or more of the components of the painting. Bituminous additives in paint are an example of one of these unstable materials.

Mould attack. All components of paintings are susceptible to mould in high-humidity conditions.

The appearance of this painting was marred by patches of mould growth. Photograph courtesy Artlab Australia, reproduced with permission of B. W. Johns

Changes due to the action of atmospheric pollutants, for example:

• colour change in pigments;

• breaking down of structural components leading to loss of strength; and

• alterations in solubility characteristics of paint films and varnishes.