When you look at your painting you probably don’t think much about the canvas support behind it. After all, unless the painting is damaged you probably can’t see the canvas. However, when you bring your piece to a studio for picture conservation, it is almost guaranteed that any damage has been caused by the failure of the canvas. It’s worth taking a minute to consider the nature of that support since every stage in the manufacture, the environmental condition of its storage, accidental damage, and any previous attempts at picture conservation of that textile support will all combine to impact the behaviour and performance of the woven fabric in its function as a fabric support for a painting.
The most likely fabric behind your painting is linen, as this has historically been the most common fibre used for artists’ canvases. Linen is produced from the flax plant. Other types of less common fabrics for support include hessian (also known as burlap). Van Gogh painted a portrait of Paul Gauguin on hessian, Rembrandt’s Self Portrait and Norman Lewis’s Girl with a Yellow Hat is a good example of oil on burlap.
More recently, artists have used cotton duck canvases such as Rothko’s Red on Maroon in the Tate Gallery.
When I assess the damage to your painting, for the most part I’ll be assessing the damage to the canvas support. For centuries, sized linen has been providing painters with a decent support for their creative expression, but it does hold some negative properties that reduce the lifespan of their work.
The fibres of the flax plant contain high levels of cellulose, and this property has some unfortunate attributes.
If your painting is brittle then there’s a good chance that the cellulose in the canvas has oxidised, a process that is accelerated if the artist or a subsequent well-intentioned restorer has used linseed or poppy seed oil as part of their picture conservation efforts. These seeds produce drying oil that contributes to the excessive absorption of oxygen by the cellulose in the fibres of the canvas. Brittleness can also be caused by mildew or other bacteria which find a favourable breeding ground in a linen canvas.
Linen is also prone to absorbing radiation, triggering a photo-chemical reaction that breaks down fibres. This effect is worsened by high atmospheric humidity and by the properties of certain pigments. Not only can airborne moisture be a problem for linen, but other atmospheric impurities, particularly those caused by pollution are corrosive.
Fibres from the flax plant are what is called hygroscopic. This means that when they absorb moisture from a humid environment the fibre cells swell, becoming shorter and thicker. This translates into shrinkage. However when the moisture dries up the fibre cells stretch out again causing the canvas to slacken and hang loosely on the stretcher.
Almost all canvas fabric whether it’s linen, hessian or cotton duck, will be treated before the painter begins to work with a glue-based layer. This achieves a more solid and stable surface, but it also leaves the canvas at risk from water damage. When water makes contact with this type of surface it transforms the solid layer into a gel-like substance causing the support to shrink. In worst case scenarios the painting may become detached from the canvas.
So when you retain me to work on your painting I will be looking at the damage that the canvas support has done and why. You will be seeing flaking paint or sagging or cracks and discolouration. I, however, will be looking behind the scene to identify and apprehend the real culprit.