The Three Little Pig (ments)
Know your C,Y, M  and K
Investigate how light and color interact by aligning three colored and one black overhead transparencies

Eric and acetate

Click on each link below and print a copy of each picture on a separate sheet of transparent acetate. Remember that you will probably have to insert the acetate sheets into your printer manually

If you cannot print on acetate with your equipment, see if your local copy center can help in transferring these images.

Align the cyan, yellow, magenta, and black acetates and hold them up to the light. (Just donít look directly into the sun.) What do you see?
Align various combinations of acetates. Now, what do you see?
Compare your four colored acetates to the full-color acetate.

If you have access to an overhead projector, project various combinations of the colored transparencies onto a screen.

Although white light contains a rainbow of colors, our eyes are only sensitive to red (R), green (G) and blue (B) light. Your brain takes the stimuli from those three colors and interprets all the other colors based on the proportion of RGB. Since human brains only processes those three colors of light, white light can be effectively described as a combination of RGB.

RGB are known as the primary colors of light. The combinations of two of the three primary colors of light produce the secondary colors of light. The secondary colors of light are cyan, yellow, and magenta. In printing, the abbreviation for cyan is "C," Yellow is "Y" and magenta is "M."

Black is usually used in conjunction with cyan, yellow, and magenta. Black helps define image details. In printing, the abbreviation for black is "K." "K" is used so that it wonít be confused with a "B" for blue. You might see the initials of these colors, CYMK, in association with various printing procedures, processes, and products.

The secondary colors of light are the primary colors of pigments or dyes (not red, yellow, and blue as many people are taught). If white light interacts with the primary colors of pigments, primary colors of light are removed.

Printed materials, like the acetates, use CYMK's ability to absorb or filter RGB colors to produce a multitude of other colors. This principle is called color subtraction (Your printer uses CYMK pigments and color substitution to make the pictures you print).

What happens to white light as it passes through colored acetate

Pigment color White light or RGB color thatís removed The colors of light that pass through
Cyan Red Blue and Green
Yellow Blue Red and Green
Magenta Green Red and Blue

The acetates you printed for this activity have regions coated with ink (cyan, yellow, magenta, or black pigments) and other regions that are not coated or clear. The amount of pigment affects the color and intensity of the light that passes through. If a layer is held up to the light, say the cyan sheet, all colors of white light pass through the clear areas. Where it is coated with cyan pigment, red light is blocked.

White light as it passes through the cyan acetate


White light as it passes through the yellow acetate


White light as it passes through the magenta acetate


If two layers are aligned, the primary colors of light may appear. For example, if a solidly colored portion of cyan acetate is held against a solidly colored portion of yellow acetate, only green light is seen. This is because cyan subtracts red light and yellow subtracts blue light, allowing only green light to pass through.

When all CYMK acetates are overlaid, depending on where you look on the acetates, various colors and various intensities are subtracted from the white light. This allows one to make an infinite number of colors from different combinations of cymk.
(Click here if you would like to see further examples of how this works.)

CYMK are the colors used in printing, too!

If you align your CYMK acetate layers and place them on top of a white sheet of paper, you will still see a full- color image. Now, imagine that you could remove the acetate but leave the CYMK pigments on the white paper. You would still see a full-color image. This is because white light hits the pigments and paper and is selectively absorbed and reflected before reaching your eye.

The process that printers use to make a full color image with cyan, yellow, magenta and black is called four color printing or four color separation.

Newspapers use CYMK in their printing process. At the base of many newspapers you can see the color separation test pattern.