Grades K–2 · Arts & Music
How does chalk leave a pale line on a board?
A chalk stick is made of material that can break into very small powdery pieces. When the stick rubs against a board, some of those pieces come off.
In the diagramChalk transfers tiny solid pieceschalk stickpowder stays here
The board’s surface catches the powder, leaving a visible line where the chalk moved. A little of the stick has become part of the mark. The line is not light shining out of the chalk.
Rubbing the mark can move its loose powder again. That is why chalk can smudge and why many chalk marks can be wiped away. A rougher or smoother surface can hold the powder differently.
About this explanation
Starting knowledge: Recognize a chalk stick and a rough drawing surface.
Sources
- Metropolitan Museum of Art — Materials and Techniques: Chalk