On a wall in the Brooklyn Museum of Art's conservation department--the museum equivalent of an intensive care unit--hangs a remarkable oddity, Forest Scene with Brook. A century ago, an early American modernist painter named Ralph Albert Blakelock put his finishing touches on the charming landscape and set it aside. Curiously, the painting never dried. The oils failed to harden, and the entire scene--like the brook itself--has been flowing slowly but inexorably toward the bottom of the canvas ever since. Museum conservators tried hanging the painting upside down to strike equilibrium, but without success. "Today the painting has slid off the canvas and onto the frame," says conservator Carolyn Tomkiewicz. "The image is a complete loss."
Blakelock’s catastrophe, Tomiewicz and her colleagues believe, was probably triggered in part by his use of a synthetic pigment known as Van Dyke brown. The pigment appears to have retarded the process of drying that has kept other oil paintings clinging to their canvases for centuries. The demise of Forest Scene with Brook illustrates a larger issue: coming up with the materials to make a painting permanent may be as big a challenge as painting it in the first place. No single method can guarantee that a painting will last, and even if the chemical composition of an artist’s paints is sound, the resulting work can still be damaged by heat, light, humidity, and the rigors of being stashed in an attic for a generation or two. To help preserve and authenticate paintings, conservators have learned to examine them using techniques more common in a morgue than in a museum. They have learned to remove a tiny core sample from a work of art, analyze it to determine the chemical makeup of pigments, varnishes, and binders, and diagnose any ailments.
Poring over flecks of paint narrower than the width of a human hair, these art doctors have explored the secrets of some of the world’s greatest paintings. When a vandal slashed Rembrandt’s The Night Watch, conservators at the Rijksmuseum in Amsterdam matched pigments and painting strokes to stitch the masterpiece together again. In the Vatican, Michelangelo’s Sistine Chapel ceiling murals took on brilliant new tones once conservators removed centuries of grime by dabbing them with a watery solution of baking soda and other mild ingredients—a technique made possible by careful examination of the layers beneath to determine what wouldn’t dissolve them. “Sometimes the surface you see is as much a result of the hand of the restorer as it is of the artist,” says James Martin, a chemist at the Williamstown Art Conservation Center in Massachusetts. Understanding the chemistry of paints and pigments helps conservators work gently as they preserve original artwork.
Pigments have a long, rich history—almost as old as humanity itself. Prehistoric people first made patterns and images by rubbing chunks of charcoal and iron oxide onto cave walls. The challenge was to make the images permanent. “There’s evidence that very early on, humans began mixing animal fats with the pigments to make them adhere better,” says Melanie Gifford of the National Gallery of Art in Washington, D.C. And as binders evolved over the years, so did artistic styles. Roman artists created striking translucent portraits by painstakingly combining pigments with hot wax, then spreading the mixture onto wooden panels. Medieval scribes frothed up eggs with water and added colors to produce elaborate illuminated manuscripts. The resulting medium, known as egg tempera, was durable because the protein denatured and became insoluble as it dried—which also explains why a splotch of egg left on a breakfast plate is so difficult to wash off.
