Optical illusions are a natural way to integrate visual art and science.  In this free STEAM lesson for grades 8-9, students will have a chance to explore a special kind of illusion.  It’s called the Watercolor Effect.

What is the Watercolor Effect?

The watercolor effect (WCE) is a phenomenon of long-range color assimilation occurring when a dark chromatic contour delineating a figure is flanked on the inside by a brighter chromatic contour; the brighter color spreads into the entire enclosed area. (Devinck, F., Hardy, J.L., Delahunt, P.B., Spillman, L., & Werner, J.S. (2006). Illusory spreading of watercolor. Journal of Vision, 6, 625-633.)

Essentially, by creating a border in a dark color and then an inside border in a lighter color, the remaining space starts to look like it’s colored in as well.  Here’s an example:

This image was found here.

See how the image on the right looks yellowed inside, while the image on the left still appears white inside the border?  That’s an optical illusion.  In today’s lesson, students explore this concept through using oil pastels, as well as various source texts.


While you could stop at just exploring the idea of the optical illusion, there’s a next step that helps students apply this even further.  After creating the illusions and exploring the effect, students then look at a variety of old maps that used this effect.  This connection to cartography provides even more context for how this effect can be applied.

Additional Resources

There are so many terrific resources out there for teaching optical illusions.  We’ve found several specific ones related to this lesson that may help your own planning and implementation:

Equip Optical Illusions Powerpoint

Color Uncovered App

Investigating Eyesight

Each of these tools provide you with extension lessons, useful applications and the powerpoint is rich with science standards and assessment items.

Like this? Be sure to visit our Lessons Page to more free arts integration and STEAM lessons like this one!

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