Shoyoukan Junior High School

Easy for everyone! Original Regenerated Chalk


Shoyoukan Junior High School


We started our research about chalk regeneration in 2002 until 2005 because we thought throwing shortened chalk away is wasteful. We received 3R Activity Promotion Award in 2011 from the mayor of Kitakyushu. Besides, we attended various events and we made regenerated chalk with more than 15,256 people.

By the way, do you know there are 2 kinds of chalk? One is plaster type chalk made by hydration bond of the sulfuric acid and the calcium. The other is the calcium carbonate chalk made by using adhesive bond.

Now, let me introduce the process of making regenerated chalk. First crash chalks and measure for 30g. If you measure 30g with 10g red and 20g White the you can make pink Chalk. If you measure 30g with 20g white and 10g yellow, then you can make cream colored chalk. Then grind and mix crashed chalks. After adding water equivalent to 60% of the mass of the chalk, and you have to knead chalk. Then you can shape anyway you want. You can make not only a shape of star, heart or other popular shape but also shape of cake, sushi and other original shaped chalk. After the shaping, dry it at a place with good ventilation for a day to two.

Currently we are researching about the relationships between water contents and drawability. We put 10% to 90% of water and measured drawability. We found out that it was most drawable when the water contents were between 50% and 70%. We also research about drying time and place. We dried chalk in both winter and summer and compared their dryness. In the winter we dried chalk at a window side, under a table and in a darkroom, a desiccator, a refrigerator and a freezer. In the summer we used an air-conditioned room instead of drying in refrigerator and freezer. We found out that the chalk can be dried at every place with high ventilation. However, in some cases, we ended up with very hard chalk which is not suitable for writing. Trying to find a factor to this phenomenon, we measured a particle size. When we made chalks with different particle size, we found out that the chalk made by the particle smaller than 0.25mm has tendency to create strong hydration bond making chalk very hard, and the chalk made with particle size greater than 0.5mm did not solidified due to gaps between particles. We concluded that the chalk made from the particle size between 0.25mm and 0.5mm has high drawability and erasability.

We would like to continue spreading knowledge about regenerated chalk to many people.