Kids, a fun event called National Chemistry Week will take place this year Nov. 4-10, 2001. Check other articles in the Bulletin and the Chicago Section web page for details in the Chicago area. The theme this year is "Celebrating Chemistry & Art". One of the related activities suggested on the American Chemical Society's website will be highlighted here.
Please note: All chemicals and experiments can entail an element of risk, and no experiments should be performed without proper adult supervision.
Fresco means "fresh" in Italian. Paintings done on wet plaster are called frescoes because the plaster is fresh; this means that the plaster is still wet when the artist paints on it. One of the most famous frescoes ever painted took four years and was finished in 1512 by Michelangelo. It was painted 70 feet above the ground on the ceiling of the Sistine Chapel in Rome, Italy. Here we'll learn the technique that Michelangelo and his helpers used to make this work of art.
The materials you will need are: a small disposable plastic dessert plate and plastic cup, a "craft stick" (popsicle stick), plaster of Paris, water, acrylic paints or poster paints, and a paintbrush. The procedure is to put 2 tablespoons (T) of plaster of Paris in a small cup, add 1 T of water, and stir with the craft stick until the mixture is smooth. Pour the wet plaster onto the plastic plate. Smooth the plaster out with the craft stick until it covers the bottom of the plate. Dip the brush into one color of paint and paint the plaster right away. Before the brush is dipped into the paint a second time, rinse the paintbrush well in a cup of rinsewater. (If the brush is not rinsed before being dipped into the paint each time, plaster will get into the paint).
Is painting on plaster different than painting on paper? Experiment with the interesting designs that can be made as the paint and paintbrush are dragged through wet plaster. What happens to the surface of the plaster as it begins to harden? Does it become more difficult to paint? When the fresco is completely dry, twist the plate gently. This will loosen the fresco so that it comes out easily.
So, what is the chemistry here? As the fresco dries, a chemical in the wet plaster called calcium sulfate hydrate combines with water and hardens before all the water can evaporate. Therefore it doesn't shrink, and the fresco can last a very long time. If your fresco is kept safe it will last a long time, too.
As an additional activity, consider entering the 2001 poster contest called "Celebrating Chemistry: Then and Now". Judging categories are grades K-2, 3-5, 6-8, and 9-12. Call the ACS Office of Community Activities at 1-800-227-5558, ext. 6097 for details.
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Kathleen Carrado Gregar, PhD, Argonne National Labs
[email protected]
November 2001
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References: Go to the website www.acs.org/ncw for general details, and to the "activities and articles" section for this activity. We also used www.artlex.com/ArtLex/p/plaster.html for this column.
