I'm not afraid of heights - a good thing when the scaffold places me thirty feet above a marble floor. Recently, I supervised the cleaning of a large Crucifixion painting in a Harlem church. The accumulated soot and grime was heavy, obscuring the painting's details and color. While removing the dirt, I saw that the artist changed his or her mind during its creation, altering details and painting over them. Over time, the underpainting began to show through the top layers, and ghosts began to appear. I always find it strangely satisfying to encounter these anomalies; they remind me that imperfection is part of us all.