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Learn an easy technique for collecting fingerprints.

This week's experiment comes from a conversation with an artist/friend. She wanted to incorporate some copper strips into her work, and was going to use some green paint to make it look old. I suggested that she would get a much more realistic look by doing it chemically, which led to an interesting experiment for us to try.

You will need:
- several pennies or pieces of copper
- vinegar
- salt
- a small bowl, jar, or drinking glass
- paper towels

Pour about an inch of vinegar into the bowl. Add about a tablespoon of salt, and give it a good stir. Then add the pennies. You should quickly notice that they become very clean and shiny as the chemical reaction dissolves any tarnish. Let the pennies sit there for about five minutes.

Remove the pennies from the bowl. Place half of them on a folded paper towel. Rinse the other half very well with water, and place them on another folded paper towel. Put them in a place where they will not be disturbed, and check on them in about an hour.

You should find that the pennies that you rinsed are still a nice, copper color, while the pennies that you did not rinse are starting to turn green. That green color is a chemical called copper acetate, the result of a chemical reaction between the copper, salt, and vinegar.

Copper acetate is one of several green chemicals that form when copper, brass, or bronze is exposed to the weather for long periods of time. The others include copper carbonate and copper chloride. Together, they are commonly called verdigris.

Verdigris has a long history of use as a green pigment for paint, but over time, it changes from green to brown, which is why very old paintings often have trees and grass that are brown. It is also used as a fungicide, as a dye for cloth, and as the main ingredient in some shark repellants.

After your copper is nice and green, you can rinse it to stop the reaction, and then rub it gently with a paper towel, until it has the appearance of a very old piece of copper. Many sculptors use a similar technique to produce the green patina on bronze statues.

Have a wonder-filled week.

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