Here are a few templates I made for students to stare at for the purpose of producing afterimages. Some of them were intended to be projected on a screen in front of the whole classroom, some were intended as individual handouts, but you could use any of them either way. Click on any of the pictures below to enlarge them to page-size.
When staring, bear in mind that the more your eye wanders, the less distinct the afterimage will be. It may help to pick a small corner or line intersection, or draw a small dot, to give you a precise point to stare at and help fix your gaze as rigidly as possible. Students will often ask if blinking is ok, and the answer is yes, as long as you don’t move your eyes. It works equally well with both eyes open, or with one eye closed, although I have a slight preference for one eye closed. The duration of the stare will depend on circumstances and how vivid you want the afterimage to be–anywhere from ten to thirty seconds, give or take.
The first two have a gray panel on the right hand side. If you stare at the black and white figure on the left then look at the blank gray right hand side, the part of your retina that received the white part of the image gets used to white, then sees gray as darker by comparison, and the part of your retina that received the black part of the image gets used to black, then sees gray as whiter by comparison.
This one has both black and white blank areas for comparison. Whichever one you look at, the afterimage is always a brighter arrow on a darker background.
What kind of afterimages do you see after you stare at colors? Try staring at the center of one of the colored circles, then shifting your gaze to the white area in the center of the page. The colors occur in opposite pairs, or “complementary colors”, each of which produces an afterimage of the other color.
Suppose we want to color a flag in complementary colors, so that we can stare at it, then look away and see an afterimage in the proper colors? We’ll need to know the proper “opposite” colors to use. For red, white, and blue flags, the opposites will by cyan, black, and yellow. (Light blue is much more common than cyan in typical small crayon or colored-pencil boxes, and is close enough to cyan for these purposes.) Here is a blank U.S. flag for students to color. Bear in mind that the more thorough and the more vivid the coloring, the more vivid the afterimage will be. I have also included a version already colored in complementary colors, and a similar pair of British Flags.