Monthly Archives: May 2014
This is another great recipe similar to the composition to the commercially available Play-Doh. It can be molded into all sorts of interesting shapes.
What you need:
- Vegetable oil
- Cream of tartar
- Food coloring
- Saucepan or beaker
- Large stirring spoon
- Heat source
- Zip-lock bag
Safety Precautions: Perform only under adult supervision. Exercise caution when using the stove. Wear safety goggles.
How to make it:
- Add 240 mL (1 cup) flour, 240 mL (1 cup) water, 5 mL (1 tsp) vegetable oil, 10 mL (2 tsp) cream of tartar, 60 mL (1/4 cup) salt, and several drops of food coloring to a saucepan.
- Stir thoroughly, until the mixture is free of all clumps.
- Heat over medium heat for about 3 minutes or until the mixture begins to thicken. Remove from heat.
- When cool, remove it from the pan. As you work it with your hands, it will develop a more pliable texture.
- For an interesting variation, make Kool-Aid play dough. Repeat the above procedure, except add a packet of unsweetened Kool-Aid in place of the food coloring to give the play dough a unique color and scent.
What to do with it:
- Play dough can be molded into a variety of shapes. It holds its shape very well.
- Play dough can be used to model virtually any scientific concept, from atoms to the solar system to parts of the cell.
- Try placing an old penny in a hunk of play dough for a few days. How does the penny look after you remove it? Can you provide an explanation for this phenomenon?
- Store the play dough in a zip-lock bag. If the play dough dries out, add water one drop at a time until it achieves the consistency you desire.
The science behind it: When heated, starch undergoes gelatinization (or thickening) in the presence of water. This is due to hydrogen bonding between the starch and water molecules. The granules of starch absorb water and swell up. This swelling begins when the temperature of the mixture reaches 60 degrees Celsius (140 degrees Fahrenheit). The starch granules become a tangled, amorphous network at this point, losing all structure. This gives the play dough its unique texture. Play dough is actually an example of a gel. A gel is a colloid where a liquid is dispersed in a solid. Other examples of gels are jelly and gelatin.
The play dough is an effective penny cleaner because it contains cream of tartar, which contains tartaric acid. Many acids are highly effective at removing corrosion from metals, and thus are excellent copper cleaners and rust removers. Other acidic substances that are effective at cleaning pennies are vinegar, lemon juice, and carbonated beverages.
The cream of tartar is used in the play dough mixture to prevent crystallization of the salt particles. Acidic substances impede crystallization. If the salt were to form crystals during the making of the play dough, it would develop a grainy texture The lack of crystallization helps to give the play dough a smooth texture.