Oil On Canvas: Painting Conservation 101

Conservation is defined as remedial attention given to extend the life of a work of art. The process often reconstitutes missing material by additions. These additions may be either visible or invisible and serve to restore the work's unity.
One of the most noticeable defects the public observes on a painted surface is craquelure. Craquelure appears as a minute crazing pattern on a painting's surface. The following layers make up a painting:
1. Stretcher bars are covered by a canvas support
2. Canvas is coated with a sizing medium
3. Gesso (a ground layer) is applied over the sizing medium
4. Paint is layered over the sizing medium
5. Varnish is capped over all these layers
Ideally all these layers dry uniformly. When the harmony of these layers is disrupted, a problem results, requiring conservation. For instance, as the different layers absorb and release moisture, expansion and contraction take place. As the materials age, the ongoing process of change can take its toll. Vibrations when art is transported can be harmful to one or more layers, even though temperature and humidity are controlled.
Returning to craquelure, it is understandable that the canvas has responds to a change in climactic conditions by either shrinking or swelling. The amount of stress might differ from the ground or paint layer. As these materials react to change differently, they result first in craquelure and finally become cleavage. Cleavage is the paint layer lifting from the canvas.
When craquelure appears as a function of age, it is generally left untouched, provided the painting is still legible. Should this condition become cleavage, a professional conservator must be consulted.
Another easily noticed problem is a slackening of the canvas, producing more "play" than was originally intended. Examine the stretcher bars. If all the corners are fixed by glue or nails and cannot be adjusted mechanically, your painting is attached to strainer bars, not stretcher bars. Stretcher bars have keys (wedges of wood that permit adjusting of the bars) or sophisticated metal elements that allow for adjustments. A canvas left for many years on strainer bars could rip once the canvas becomes brittle.
Yellowing or darkening varnish is another readily recognizable issue. About every 25 years, review canvases for a re-application of varnish. First the original varnish must be removed by a professional conservator.
Frequently-Asked Questions
How do I find a good conservator? American Institute of Conservation in Washington, DC 202 452-9545 is one source of competent people. Call your local large museums for recommendations as well as art appraisers in your area.
What can I expect from a conservator? It is customary for you to be provided
a) Estimated cost of treatment
b) Estimated time to complete the treatment
c) Conservator's steps to complete treatment
d) Anticipated result from the treatment (identification of what is possible to remedy and to what degree)
How are the fees assessed? Conservators guestimate the number of hours needed to complete the work (based on their past experience).
Word of caution: Find out if your conservator has insurance and if so, how much and what are the limitations of their coverage. If they do not, call your insurance company to find out their position on insuring your property while it is in the hands of a conservator.