Abstract

Objective

Determine how different colors of light affect the brightness of a sun-print image.

Introduction

Take water, sunshine, and some creativity, and what have you got? Hours of enjoyment, making photographic-type pictures, called sun prints, shown below in Figure 1. Sun prints are made on special sun-print paper, which can be used to make images of all sorts of objects. To make a sun print, place an interesting object on a sheet of sun-print paper, expose it to the sun for a few minutes, dip the paper in water, and watch as a permanent image appears.

Figure 1. Sun prints of a flower and of some household items.

When you expose sun-print paper to sunlight, and then rinse the paper with water, the areas of the paper that were exposed to sunlight appear dark blue. If there is an object blocking the sunlight, the paper under the object appears white. Sun-print paper has a light-sensitive chemical soaked into the paper. This chemical (called Berlin green) is a light-green color and it washes away when the paper is soaked in water. The chemical washes away because it dissolves in water (which means the chemical is water-soluble). When light hits the chemical Berlin green, it causes a light-activated chemical reaction. The product of the chemical reaction is a dark blue chemical, called Prussian blue, that does not wash away in water (meaning it is insoluble in water). Because the Berlin green washes off and the Prussian blue formed by the chemical reaction with light stays on the paper when rinsed, the areas that were shaded by the objects form white images on a blue background.

Sunlight is made up of red, orange, yellow, green, blue, and purple light. You can see the different colors of light that form sunlight when you look at a rainbow. When you expose the sun print to sunlight, all of these colors of light hit the chemicals in the paper. The goal of this chemistry science fair project is to determine which of the various colors of light that make up sunlight are best at forming images on sun-print paper. In the experimental procedure, below, you will write on a clear piece of plastic with permanent markers of different colors. This plastic with colored patterns on it will then be placed over the sun-print paper and the paper will be exposed to sunlight. The colored ink forms a sort of light filter. For example, the red ink will allow mostly red light through to the paper, while green ink will allow mostly green light through to the paper. If you have all of the colors of the rainbow on the plastic, which ones will form the brightest image when the paper is rinsed?

Terms, Concepts, and Questions to Start Background Research

• Sun print
• Light-sensitive chemical
• Berlin green
• Water-soluble
• Chemical reaction
• Product of a chemical reaction
• Prussian blue
• Insoluble
• Light filter
• Particle
• Trial

Questions

• Based on your research, what are the primary colors?
• Why do you rinse the sun-print paper after exposing it to sunlight?
• What are some water-soluble chemicals that you can find in your kitchen? What about insoluble?

Bibliography

• Lamb, A. and Johnson, L. (2002, July). Color. Retrieved November 24, 2009, from http://42explore.com/color.htm

Materials and Equipment

• Clear plastic sheet protector; available at any office supply store
• Ruler, metric
• Scissors
• Sun-print paper; available online from Lawrence Hall of Science's store at lawrencehallofscience.stores.yahoo.net/sun printkits.html
• Permanent markers, chisel tip; red, orange, yellow, green, blue, and purple
• Timer
• Cardboard, 30- x 30-cm piece
• Water
• Lab notebook

Experimental Procedure

1. Assemble the sun-print kit and other materials.
2. Cut a 10-cm x 15-cm rectangle from the sheet protector plastic.
3. Label the piece "#1" with small print in the upper left corner with the black permanent marker. This represents that this is your first trial.
4. Write the following three-letter words on the plastic sheet, using the color of ink that is listed. You can use any pattern you like for the placement of the words, but keep the size of the letters the same.
   1. RED in red ink
   2. ORA in orange ink
   3. YEL in yellow ink
   4. GRE in green ink
   5. BLU in blue ink
   6. PUR in purple ink
5. Cut a 10-cm by 15-cm piece of sun-print paper.
6. Following the directions that came with your sun-print kit, make a sun print using the plastic sheet.
7. Expose it to sunlight for 2 minutes. Use the timer to help you keep track of the time.
8. Cover the sun print with the cardboard to stop the reaction at 2 minutes.
9. Bring it inside and rinse and dry the paper.
10. Look at your results.
11. Make a data table for this trial in your lab notebook with each of the colors that you used.
    1. List the colors in order, with the color that has the brightest letters first.
12. Repeat steps 2–11 two more times. This ensures that your results are accurate and can be repeated.
    1. Label the new plastic sheets in step 3 "#2" and "#3" for each new trial (a total of three trials).
13. Based on your results, which colors form strong, weak, or no images? Can you see a pattern in the results? Remember, colors that form images are colors that do not cause the chemical reaction that forms Prussian blue.

Variations

• Try using colored lights. Which colors of light are best at forming sun-print images?
• Is ultraviolet light required for the sun-print reaction? Use clear items that block ultraviolet light, such as glass, to test this. You can also see if sunscreen on plastic sheets forms an image.
• Look up the wavelengths of the different-colored light. Add this data to the table.
• Add a column to your data table that has the complementary color for each color of ink you used. Analyze your results in terms of which colors are blocked by the colored ink.

• For more science project ideas in this area of science, see Chemistry Project Ideas.

Credits

David B. Whyte, PhD, Science Buddies

Last edit date: 2009-10-05 09:27:00