Background. Our perception of the colors in a painting depends on the nature of the light illuminating the artwork as well as the material of the painting itself. Sunlight is composed of a mixture of multiple wavelengths of electromagnetic radiation, resolvable into its components with a prism to produce a continuous spectrum. A white light source contains equal intensities of these multiple wavelengths.

The common incandescent bulb also produces a continuous spectrum (right) but contains higher intensities of the yellow light so that objects appear more yellow when illuminated by this source rather than by sunlight. In contrast to such continuous spectra, heating gaseous elements produces light of only selected wavelengths, a line spectrum such as that from
hydrogen (right). Efforts to understand such line spectra led to the modern view of atomic structure. The wavelengths of line spectra are characteristic of the element from which they are generated and can be used to identify unknowns. (Color Lab 1: Spectroscopy of Atoms and Colors).

Isaac Newton was the first to discover that mixing light of three colors from the above rainbow regenerated white light. He called these three colors--red, blue, and green--the primary colors. Combining light of two primaries give the secondary colors: Blue and green yields cyan; blue and red, magenta; and red and green, yellow. Such additive mixing of colored lights produce dramatic effects in theatrical lighting as well as form the basis for color TV and computer monitors. The inside of the screen is coated with materials that emit red, blue, or green light when stimulated by electrons. A yellow patch on the screen results from light emitted by red and green phosphors. These individual areas may be observed with a magnifying glass.

In contrast to additive color mixing of lights, the subtractive mixing of color leads to the removal of certain wavelengths of light by absorption by an object. Consequently, the color we observe comes from the light reflected from the object: the components of the light source minus the colors absorbed. The paint producing the blue of a Renoir painting (Chemistry 103 Homepage) absorbs—or subtracts—red and green but reflects blue light to our eyes.

References
1. Taft, W. Stanley, Jr. and Mayer, James W. (2000) The Science of Painting. New York: Springer-Verlag. Chapter 5, pp. 50-65.
2. Hampton-Sidney art and chemistry web site: http://cator.hsc.edu/~mollusk/ChemArt/paint/color.html.
3. Overheim, R. Daniel and Wagner, David L. (1982) Light and Color. New York: John Wiley & Sons, Inc. Chapter 2, "The Origin of Color," discusses the connection between theories of atomic structure and light (Section 2.3) and the relationships between reflected, transmitted, and absorbed light. Chapter 3, "Colorimetry, describing and measuring color," provides a good overview of the different color measuring systems.
4. Billmeyer, Fred W., Jr. and Saltzman, Max. (1981) Principles of Color Technology, 2nd Edition. New York: Wiley-Interscience.
5. Billmeyer, Jr., Fred W. (1981) "Color and the appearance of objects." Journal of Chemical Education. 58: 367.

Experiments
1. Color lab 1-Download PDF: Spectroscopy of Atoms and Color
2. Color lab 2-Download PDF: Absorption and Reflection of Light
3. Directions for using Ocean Optics spectrophotometer to obtain absorbance and transmittance spectra Light.
DownloadPDF: Directions

Links
1. Hampton-Sidney art and chemistry web site: http://cator.hsc.edu/~mollusk/ChemArt/paint/color.html.
2. University of Arizona course "Patterns in Nature:"
a. Color: http://acept.la.asu.edu/PiN/rdg/color/color.shtml
b. Optical spectroscopy and atomic structure: http://acept.la.asu.edu/PiN/rdg/optical/optical.shtml
3. Basic ideas regarding nature of light: http://micro.magnet.fsu.edu/search/index.asp which is part of a larger site on microscopy: http://micro.magnet.fsu.edu/primer/index.html
4. Glossary of color science: http://tigger.uic.edu/~hilbert/Glossary.html#Subtractive_mixture
5. Chemistry of autumn colors: http://scifun.chem.wisc.edu/chemweek/fallcolr/fallcolr.html

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• Professor Margaret Merritt, Wellesley College Chemistry Department
  
• Created by: Leslie Chang '04 & Jerina Hajno '04
  
• Page Created: July 23, 2001
  
• Last Modified: August 10, 2001
  
• Page Expires: August 31, 2002