Black is not Black
by Franz Kogler
5th Grade Individual
Grand Prize

Problem

Is the color black in markers only made out of a black dye?

Hypothesis

If I can separate different colors from a black marker, then I will get a set of basic dyes (colors), because color mixtures can be separated into its components by chromatography.

Color itself is a physical phenomenon, which means colors are different wavelengths of the visible light that are emitted or reflected from an object. White light includes the colors red, orange, yellow, green, blue, indigo, and violet (spectrum). Each of them has a certain wavelength.

A color sensation is created by two different physical phenomena, color subtraction and color addition.

The process of color subtraction colors things that do not produce light themselves. When an object is illuminated by white light the pigments or dyes of the object absorb parts of the light (= subtract color of the white light). The absorption of a specific wavelength (color) is a function of the chemical structure of the dye or pigment. The unabsorbed part of the light is reflected and produces the color of the object. If there is no colored light reflected, we perceive black.

Only the reflected wavelength (color) of the light passes our eye. The cones of the retina contain three different pigments. Each of them responds only one of the three primary colors of light, red, green, or blue. Usually colored light is a mixture of colors (wavelengths and/ or intensities of the components). This causes a reaction of more than one pigment. Then the process of color addition produces the color sensation. Therefore we see white light white although it contains the whole spectrum.

What happens to white light if it shines on a black dot?

I selected marker # 2 for my explanation. It contained yellow, magenta, and cyan.

Each component of the black color absorbs (subtracts) a particular color of the white light. There is no color to be reflected. I see black.

What happens in my eye if it perceives green and red light of equal intensity?

Green and red are two primary colors. Therefore two pigments of the cones respond and add the green and red light to yellow. I see yellow as if a yellow light would strike my eye.

Materials

Procedure

1. Draw a line with a pencil 1.2cm from the end of the filter paper strip (Chromatography Paper 4"x 1" from Auspex Scientific).
2. Make a small black dot with a black marker on the pencil line and let it dry.
3. Attach the filter to a stick (wooden barbecue spit) with a paper clip.
4. Pour water (Albertson’s Drinking Water) into a bowl until it is deep enough to just touch the bottom of a suspended strip of filter paper.
5. Place the stick on the edge of the bowl and be sure that the water does not touch the color dot and the filter does not stick to the side of the bowl.
6. Allow the water to rise on the filter until it is near to the top of the filter or the color stops moving.
7. Remove the filter and allow it to air dry.
8. Repeat the experiment with other brands of black markers.
9. Observe and record if and how the color spot changed and compare the different filter strips.

Variables

Manipulated Variable

Different brands of markers

Responding Variable

The presence of dyes others than black

Controlled Variables

Same kind of water, filter paper, size of strip, location of dot, conditions

Results

Only one marker I tested (# 5) contained a black dye, besides two others, green and purple. The color black of all other brands was at least a mixture of three dyes others than black. One marker (# 5) didn’t exhibit yellow and two (# 4, 5) not magenta and cyan. The main components of five markers (# 1, 2, 3, 6, 7) were yellow, magenta and cyan. I could identify a purple dye in three markers (# 3, 4, 7).

Conclusion

A separation of different dyes from a black color worked with all markers in all three experimental series, but the separation was not always complete.

Although unclear borders between the dyes and very low intensity of a dye caused problems to estimate the travel distances at some filter strips, I found out that some different markers contain identical dyes (See chart: Comparison of dyes of different markers).

Moreover I discovered that the color black can be produced by mixing different dyes and rarely contains black itself.

I wanted to know why I always saw black, although the "blacks" were made out of such different colorings as yellow, magenta and cyan or blue, yellow and purple. Therefore I studied the physics of light.

• Newmark, Ann. Chemistry. New York, NY: DK Publishing, Inc., 1999.
• Burnie, David. Light. New York, NY: DK Publishing, Inc., 1999.
• Robson, Pam. Light Color& Lenses. New York, NY: Shooting Star Press, Inc., 1995.
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• The Hutchinson Dictionary of Science. Helicon Publishing, Ltd., 1999.
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• Encarta 2000. Microsoft Corporation, 1999.
• Analysis of Mr. Sketch Ink by Paper Chromatography. [ 10/30/00] . wwwchem.csustan.edu/chem1002/mrsketch.htm
• The Gene School – Paper Chromatography. [ 10/30/00]. library.thinkquest.org/19037/paper_chromatography.html
• Paper Chromatography. [10/30/00]. 155.135.31.26/oliver/satcoll/paperchrom.htm

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