Infrared reflectography can be used to reveal underdrawing and some overpainted passages not visible to the naked eye. Infrared (IR) light (heat) can penetrate upper paint layers but is differently absorbed by different pigments. Charcoal underdrawing applied to a white ground produces the strongest contrast and the clearest infrared image. The heat, reflected by the white ground and absorbed by the black line drawing, can be captured by an IR-sensitive camera.