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Saturday Science: Eggshell Sidewalk Chalk

Did you make omelettes, scrambled eggs or maybe a frittata for your family’s Saturday morning breakfast? Don’t throw away those eggshells! Use them for this week’s Saturday Science experiment, courtesy of Almost Unschoolers


  • Eggshells
  • A clean rock 
  • Hot water 
  • Flour 
  • Food coloring 
  • Mixing bowl 
  • Mixing spoon
  • Paper towels (or paper napkins) 


  1. Wash out the eggshells and allow them to dry completely. 
  2. Use a clean rock (or mortar and pestle) to smash the eggshells into a fine powder.
  3. For each piece of chalk, add one spoonful of eggshell powder, one teaspoon hot water, one teaspoon flour and a few drops of food coloring to your mixing bowl and mix ingredients together. 
  4. Pour chalk paste onto a paper towel and roll it so that it is the shape of a long piece of chalk. 
  5. Let dry for at least three days. 
  6. Peel the napkin or paper towel off of your chalk. 
  7. Take your chalk outside and start drawing! (Note: To prevent scratches, do not use this chalk on a chalkboard.) 

Did your eggshell sidewalk chalk allow you to draw beautiful sidewalk pictures just like the chalk that can be bought in a store? 

Store-bought sidewalk chalk is made from a combination of calcium carbonate, gypsum, silica, phosphorus, iron, alumina, phosphorus, sulfur, manganese, copper, titanium, sodium oxide, fluorine, strontium and arsenic. Its main ingredient, however, is calcium carbonate – a form of limestone. Calcium carbonate (CaCO3) is the chemical that lets us draw on the sidewalk with a piece of chalk.

Do you know what else contains calcium carbonate? Eggshells! This makes them a great alternative to store-bought chalk. 


Want more Saturday Science? See all of our at-home activities on the blog or on Pinterest.

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Categories: Science
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