Why infrared?   The basic problem solved by making images of the way the Bonampak murals reflect infrared light is the problem of seeing the black pigments on the wall (which define much of the detail) without having the other pigments get in the way. All substances have characteristic ways of absorbing different wavelengths of light, dependent on the molecular structure of the substance. Wavelengths that aren't absorbed are reflected, again in a characteristic pattern, and the combination of wavelengths composing this reflected light is perceived by the eye as color. A splash of green paint, for example, absorbs red light (wavelength around 700 nm) very well. However, it doesn't effectively absorb light with a wavelength around 500 nm, which is reflected back to your eye and perceived as green. Recording the variation in infrared rather than visible light reflected from the painted wall has two helpful effects: 1. Most of the colored pigments don't absorb much light from this part of the infrared. They instead reflect it back to the sensor. These areas appear white or light grey in the infrared images.   2. The black pigment, because of a high carbon content, absorbs infrared rather than reflecting it back to the sensor. Areas covered with black therefore appear dark, so the black is distinguished from other pigments more strongly in an image based on infrared reflectance than in an image based on visible light reflectance.