Department of Energy Argonne National Laboratory Office of Science NEWTON's Homepage NEWTON's Homepage
NEWTON, Ask A Scientist!
NEWTON Home Page NEWTON Teachers Visit Our Archives Ask A Question How To Ask A Question Question of the Week Our Expert Scientists Volunteer at NEWTON! Frequently Asked Questions Referencing NEWTON About NEWTON About Ask A Scientist Education At Argonne UV, IR, and Color Theory
Name: Emma S.
Status: student
Age: 17
Location: N/A
Country: N/A
Date: 3/11/2004

I am a high school student currently undertaking an assignment. My question is, how does the use of infra-red and ultra-violet spectroscopy (in identifying pigments) relate to the colour theory?

A complete answer to your inquiry would require several books. However, the short answer is this:

Infrared spectroscopy is very useful for identifying the presence of particular types of functional groups because various functional groups tend to have similar vibrational frequencies independent of other groups that might be present. In addition, the infrared spectrum can distinguish organic pigments from inorganic mineral pigments. The organic pigments tend to have fairly sharp absorptions in the 300 to 3000 cm^-1(wavenumber) range, whereas inorganic pigments tend to have very broad absorptions. One caution here though -- a commercial pigment may contain both inorganic and organic components so this distinction may be confounded. Ultraviolet spectroscopy measures the electromagnetic radiation absorbed by the pigment in the wavelength range of about 400 to about 250 nanometers (sorry about the change from wave numbers to wavelengths, but that is the conventional way the absorptions are expressed in the two regions). In both organic and inorganic pigments these absorptions are characteristic, but are usually broad in both cases.

The ultraviolet spectrum absorptions are also characteristic of the chromophore (absorbing species) even in cases where the ultraviolet absorption is not the one that gives rise to the color of the pigment. Substances that absorb in the visible range of the spectrum -- 400 to 700 nanometers -- almost always have other absorptions at shorter wavelengths in the ultraviolet too.

How these spectra relate to the theory of color is much more involved, because the "theory" of color is very complicated because "color" is a visual perception, not an instrumentally measurable property of matter. A loose acoustic analogy would be to ask how does wave motion affect the sound of a symphony orchestra? There certainly is a relation, but a detailed explanation would be very involved.

Vince Calder

Click here to return to the Physics Archives

NEWTON is an electronic community for Science, Math, and Computer Science K-12 Educators, sponsored and operated by Argonne National Laboratory's Educational Programs, Andrew Skipor, Ph.D., Head of Educational Programs.

For assistance with NEWTON contact a System Operator (, or at Argonne's Educational Programs

Educational Programs
Building 360
9700 S. Cass Ave.
Argonne, Illinois
60439-4845, USA
Update: June 2012
Weclome To Newton

Argonne National Laboratory