In this coffee filter painting STEM activity, we stumbled upon a surprise science lesson about capillary action.
Capillary Action is the movement of water through a medium because water molecules like to stick to other water molecules, and stick to other substances.
When the boys painted the coffee filters, the watercolors went straight through the coffee filter! So, what was going on?
Coffee filters are semipermeable membranes, which is why they are used in filtration to make coffee. Semipermeable membranes allow for some molecules to pass through, and others not. A coffee filter holds back the coffee grounds, but water, flavor, and caffeine pass through the filter into our cups. I had an idea that would allow us to capture our coffee filter paintings through the semipermeable membrane coffee filter.
Coffee Filter Painting – Learning About Semipermeable Membranes
- Fill the small plastic paint cups with water, then add watercolors from tubes for desired colors. We chose red, yellow, green, blue, and purple.
- Place a coffee filter on top of one sheet of watercolor paper. I also place a wipe-able place mat under the watercolor paper.
- Paint the coffee filter using the pipettes and watercolors. Drop one drop of water color at a time and watch how the paint spreads through the coffee filter. The paint moves due to capillary action.
- Your little ones might want to push down all the bubbles made when the paint is dripped on the coffee filter
- Slowly lift the coffee filter to see the final design on the watercolor paper!
- Here are the just-created designs before drying.
- Let the painting dry completely before displaying.
The Science Behind Coffee Filter Painting
If you are using this coffee filter painting activity with older students to demonstrate capillary action and/or osmosis, here is an explanation to use to help generate discussion about what students observed during the activity.
The porous structure of the paper allows water molecules from the paint to move through tiny spaces within the paper fibers.
Once the watercolor paint is absorbed by the coffee filter, the paint begins to diffuse through the paper. Diffusion is the movement of molecules from an area of higher concentration to an area of lower concentration. As the watercolor pigment molecules spread out within the paper fibers, they encounter the surface of the paper underneath the coffee filter.
When the paint watercolor pigment molecules reach the surface of the paper underneath the coffee filter, they can be absorbed by this paper as well. This absorption occurs because the watercolor paper is also porous.
The extent to which the paint soaks through to the watercolor paper depends on factors such as the saturation of the coffee filter with paint, the thickness and absorbency of the coffee filter, and the thickness and absorbency of the underlying watercolor paper, and the capillary action within both materials. If the coffee filter is heavily saturated with paint, or if the underlying paper is highly absorbent, more paint is likely to soak through.
I hold a master’s degree in child development and early education and am working on a post-baccalaureate in biology. I spent 15 years working for a biotechnology company developing IT systems in DNA testing laboratories across the US. I taught K4 in a private school, homeschooled my children, and have taught on the mission field in southern Asia. For 4 years, I served on our state’s FIRST Lego League tournament Board and served as the Judging Director. I own thehomeschoolscientist and also write a regular science column for Homeschooling Today Magazine. You’ll also find my writings on the CTCMath blog. Through this site, I have authored over 50 math and science resources.