Kids, in this experiment we will be making imprints of objects and then coloring them "chemically" to a beautiful blue-purple (indigo) shade. You will need a 3-inch square piece of architect paper, any solid object to imprint (key, coins, paper cut-out letters, etc.), an empty, clean peanut butter jar with its lid, 1/2-cup household ammonia, several small rocks or pebbles to cover the bottom of the jar to about 2-inches in height, and a bright light (such as a desk lamp).

Please note:  All chemicals and experiments can entail an element of risk, and no experiments should be performed without proper adult supervision.

Place your solid object on the yellow side of the architect paper. Let it sit under a bright light for about five minutes. While waiting, place the rocks in the jar and have your adult partner add the ammonia. Make sure the liquid is just below the surface of the rocks. Cover the jar tightly with the lid. Remove your solid object from the light and notice the "imprint" it left on the paper. Open the jar and carefully place the paper inside, taking care to not let the paper touch the ammonia. Re-cover tightly and observe the paper for about 5-10 minutes.

The ammonia fumes will turn the imprint a deep blue purple color, leaving the rest of the paper alone. The light has chemically altered the unprotected surfaces of the paper so that it will no longer react with the ammonia, which is a chemical base. Architect paper is a very light-sensitive material, but your object has protected and preserved a small portion of it.

When you are finished, have your adult partner pour the ammonia down the drain and clean the jar and rocks with warm soapy water.

Take care not to inhale the ammonia fumes at any point during your experiment.

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Kathleen Carrado Gregar, PhD, Argonne National Labs 
[email protected]
January 1996

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Reference: Phil Parratore, Wacky Science: A Cookbook for Elementary Teachers, Kendall-Hunt Publ., Dubuque, Iowa, 1994, page 76.