Stephanie Chasteen

Exploratorium Teacher Institute

© 2006 Exploratorium, all rights reserved

The spectrum at your fingertips

Introduction Your nails can be a fun way to show the different ways that colors can be categorized. Materials Hands, nails, and nail polish. To Do and Notice Paint your nails in 10 different colors. We have two different schemes, but you could come up with many more:

The expanded spectrum:

CYMK and RGB

Black =infrared Red Orange Yellow Green Turquoise Blue Indigo Violet White or clear = ultraviolet

Black Red Orange Yellow Green Cyan Blue Magenta Violet White

What’s Going On? Project a spectrum and ask your students how many colors they see – they’ll often identify a small numer, like 5 or 7. We teach that the spectrum is made of ROYGBIV but that is actually an artifact of history (see Etc). The choice of these 7 colors is rather arbitrary, since the hues vary continuously from one to the other in a spectrum. Thus, the expanded spectrum gives another example of how the

Stephanie Chasteen

Exploratorium Teacher Institute

© 2006 Exploratorium, all rights reserved

spectrum can be broken down, as well as adding the “invisible” colors (infrared and ultraviolet) that we can’t see (but other animals can). Another way to represent colors is by the different sets of primary colors. Primary colors are those sets of colors that can be mixed to obtain every other possible color. In most inkjet printers the primaries used are CYMK (cyan, yellow, magenta, black) are the primaries – these are used in light mixing. Pigment mixing is usually done with RGB (red, green, blue). Mixing RGB pigments will give black (the left pinky finger) and mixing CYM lights will give white (the right pinky finger). Notice that magenta and cyan do not appear in the light spectrum. No single wavelength of light produces the perception of magenta or cyan. The same is true of white light. Etc. Newton chose 7 colors to correspond to the 7 named musical notes in an octave (do-re-me-fe-so-la-ti-do). He originally identified only 5, later adding orange and indigo to fill out the full 7. While this helped Newton in explaining the new theory, it is a flawed comparison (the frequencies of musical notes follow a geometric progression, whereas the same is not true of the color spectrum) – and Newton realized this. Other spectra activities: Colored shadows (light mixing): http://www.exo.net/~pauld/summer_institute/summer_day6color/colored_shadow_exploration.html Colors of nature: http://www.exo.net/~pauld/summer_institute/summer_day6color/colorofnature.html Spectrum photo credit: National Optical Astronomy Observatory/Association of Universities for Research in Astronomy/National Science Foundation. Black lines are Fraunhofer lines.