All materials change with the passage of time, and react to the effects of handling and environment. Materials also interact with each other. An aspect of the conservation profession is a perpetual assessment of materials the sources of materials, their use, how they change, and why.
Paintings are basically layers of materials applied upon a support. A support may be any type of material, such as canvas, panel, paper, metal, bone or stone. Contemporary artwork may include whatever materials an artist's inventive mind can imagine.
White fungus on an oil on canvas painting.
Initially, materials may have alluring malleable and aesthetic qualities. Temperature, light, moisture, and natural degeneration affect materials. Heat and light accelerate aging. Materials become brittle and degrade. Panels or canvas supports may warp or develop wave-like distortion. Materials may also flake, fade, or darken. Moisture can stain and decay materials. Bloom resulting from high humidity is a whitish haze that can visually disfigure an artwork's surface. If a material is too wet, fungus may occur, and the material may just slush away.
One elementary interaction of materials is the contraction and expansion that occurs due to changes in humidity and temperature. As a material ages it becomes less capable of recovering from these natural physical actions.
There are also cracks or craquelure. In conservation, crack classifications are defined as primary, secondary, and mechanical. Primary craquelure can develop in the ground, paint, or varnish layers as the artwork dries, for example, when a faster drying layer is applied over a slower drying layer or within extremely thick or lean layers of paint. Artificial dryers and additives to paint can make it crack. In the 19th century, the use of bitumen often caused alligator crack patterns that deformed many paintings. Sometimes painters intentionally induce crack patterns for contrived signs of corrosion and synthetic patinas.
Cracking on an oil on canvas painting.
Secondary cracks develop as a response to aging and environmental stresses. Desiccated layers may crack, separate and detach. Fine cracking or crazing occurs when a varnish layer becomes very old. Problems may arise if heavy applications of paint or weighty mixed media are used on comparatively scant supports. Thick paint pulls away from a canvas support or the canvas shrinks, sags or distorts. A panel painting may develop cracks due to the shrinkage of the wood. Structural weakness or damage to an artwork may develop over time.
Mechanical cracks are the result of outside influences. Crack rings or spirals can occur when an object is knocked against an artwork. Scratches or rubbed areas may result in feather pattern cracks. Fragile areas require professional care by a trained conservator.
A patina of stable cracks is a part of an artwork's character, charm and history. When viewing an artwork, its collection of cracks can offer insight into its past. Be a detective. What is your artwork telling you?