"I once worked on a small panel painting that was so completely covered in cat hair stuck in the

Detail of Jackson Pollock’s “Number 7, 1951,” enamel on canvas, before cleaning by the National Gallery of Art’s Painting Conservation Department for a large stain and irregular tide lines in the upper, left-hand corner, as well as wear, dirt, vandalism and stains.

dark brown varnish that the image could not be seen,” says Alexandra Tice, a Chevy Chase, Maryland–based painting conservator with 30 years’ experience. “When hair and varnish were removed, the work of a Dutch master was revealed.” A detailed assessment of the painting—including the condition of the paint, canvas and stretcher—revealed that aside from its hirsute state, little beyond relatively minor restoration (removal of the old varnish and the application of a new coat) was required to prolong its life, the goal of conservation. In fact, Tice encountered several conditions conservators often see in older paintings: grime and discolored varnish, tears and holes, flaking paint and poor previous restoration.

Jay Krueger, senior conservator of modern paintings at the National Gallery of Art in Washington, D.C., says a fundamental difference between old and new paintings is that many contemporary artists don’t use varnish, thus leaving the works exposed to hazards like food stains. He is currently treating a Frank Stella painting that was squirted with ketchup, which has eaten away portions of the top layer of paint and has resulted in blotchy white patches. (Ketchup, Krueger says, is “chemically very complex, an acidic product that contains salt and sugar.”) Other culprits include pencils, since graphite is insoluble, and fingerprints, which attract dirt and dust.

Krueger says contemporary works, particularly those involving found or biodegradable objects, present new challenges for the conservator. Anselm Kiefer, for example, occasionally includes wood, straw, dried flowers and other fragile and decaying objects in his paintings. To complicate matters, he creates some works by torching the paint surfaces, exposing them to the elements to accelerate the degradation process and rolling and folding painted canvas. It’s no surprise, then, that Krueger has a bag of “Kiefer pieces” containing shards and fragments that have fallen off the museum’s monumental “Zim-Zum.” To stabilize the painting, he has carefully introduced adhesive beneath areas that are likely to flake. Other artists, such as Sean Scully, are more orthodox in their techniques and materials. Asked what he does to ensure that his paintings don’t require conservation, Scully responds, “I use very expensive paint, I follow standard, accepted practices and I don’t experiment.”

One of the virtues of collecting contemporary work, according to Mark Coetzee, director of the Rubell Family Collection in Miami, is that we usually see works fresh from the studio and as the artist intended. To ensure that that intent is preserved, each of the more than 6,000 works in the collection has been extensively examined and photographed, and these documents can be used as a guide should a work require conservation. Coetzee also takes a pre-emptive approach, which includes occasionally replacing original stretchers (“because some young artists use poor-quality merchandise”), stockpiling paint specific to an artist and, when possible, consulting the artist directly.