Ancient Color

Ancient Color

Creating Using Investigating

Investigating Color with Light

Fiber optic reflectance spectroscopy of a Fayum portrait
Visible light image of Bacchus’s hair and ivy-leaf garland (left); VIL image of the same view showing Egyptian blue luminescence (right).

Ancient pigments and dyes interact with light in different, characteristic ways. Light is a form of radiation that is made up of several different wavelengths. Among these are visible light, which helps us to see, ultraviolet light, which is used in crime-scene investigation, and infrared light, which is used for night vision.

Multispectral imaging (MSI) is a photographic technique that captures the reflectance and luminescence responses of artifact paint surfaces under these different light sources. At the Kelsey Museum we frequently use an MSI technique called visible-induced infrared luminescence (VIL), which can locate and identify even trace amounts of the pigment Egyptian blue on an artifact’s surface. With this technique, Egyptian blue pigment will appear to glow as it emits infrared light after being exposed to certain wavelengths of visible light.

Another technique, called fiber optic reflectance spectroscopy (FORS), involves directing different wavelengths of light onto the painted surface of an artifact using an optical fiber bundle. The FORS instrument measures which wavelengths of light are absorbed or reflected by the painted surface, which can be used to identify pigments or dyes present in the paint.