Grades K–2 · Materials & Matter
Why can a wet patch of cloth look darker?
A splash of clear water can make colored cloth look darker. The water has not necessarily added dark paint. It has changed how light travels around the cloth’s tiny fibers.
In the diagramWater can change light returning from clothdrywet
Dry fibers have many spaces filled with air. When water fills some of those spaces, less light may scatter straight back out. More light can travel within the cloth, where its colored material absorbs some of it.
With less light returning toward your eyes, the wet patch can look darker. When the water dries away, the earlier appearance often returns. The result also depends on the cloth and the direction of the light.
About this explanation
Starting knowledge: Know that we see a surface when light from it reaches our eyes.
Sources
- Hao Cui, Yuan Sun and Renzo Shamey, AATCC Journal of Research — Visual and instrumental assessment of moisture-induced color change in polyester fabrics