Introduction: KONY 2012 Chalk Stamp
This is an alternative to the chalk stencil Invisible Children has suggested. With this stamp, you can simply dip it in red chalk powder (available at hardware stores for refilling chalk-lines) and press it on a surface. It should be quicker, easier, and probably less wasteful of chalk than shaking chalk powder through a stencil with a paintbrush. You could also use this technique to make stencils with other images, depending on the size of your foam block and desired image.
You will need a foam block, the stencil template from the Cover the Night Digital Action Kit, some tape that will stick to both, and a knife. Scissors may also be helpful. The foam block I used came from some packaging. My parents tried to throw it out, but I saved it because I knew I could find a use for it. It happens to have three holes in the back that make a passable handle.
Warning: Don't be stupid like me and make your stamp the same way around as the stencil! Make sure you flip the template horizontally before/when you print it. I'm going to use the extra foam I cut off in step 3 to redo the text. Also, if you use a molded surface of closed-cell foam, you'll probably have to roughen it for the chalk to stick.
Step 1: Print and Tape Template
Download the Digital Action Kit, if you haven't already, and print the chalk stencil. Make sure you flip it horizontally! You may find an option to flip it in the print settings; otherwise, you'll have to flip it before you print it. Tape your printed template onto your foam block. If the size of your foam block requires accurate registration of the template, you can hold it up to a light/window/sun to check the alignment.
Step 2: Start Cutting
Using the knife, cut through the paper into the foam. Don't worry about extra cuts outside the letters, because you're going to carve that foam away anyway. In fact, I recommend cutting along the top and bottom of the text to make the foam easier to remove.
For the O and 0, cut the inner line first. For the 2s, cut inside the top first. For the O, 0, and Fourth Estate, ignore the support lines. This isn't a stencil, so they aren't necessary.
I found I had to add some more tape when I cut out the Fourth Estate.
Try to cut to an approximately uniform depth. I went about half a centimetre at first. When you finish cutting out a section, go back through the cuts with the knife to make sure they're cut cleanly to full depth.
Finally, remove the paper.
Step 3: Remove Excess Material
Now you can begin cutting out the negative space. I started in the middle of the Fourth Estate, because I wanted to practice on an easy part before attempting the text. Cut sideways with the knife, and pull or pry the foam out. My block was made of laminated foam, which may have made this easier. Scissors may be helpful for cleaning up small bits.
Partway through this step, I decided to cut off the extra foam at the top of my stamp. Later, I cut off the extra foam around the bottom.
When you've cut all of the negative space away to some depth, go back over it to clean it up and deepen it if necessary.
If you damage part of the foam that you want to keep, you can glue it back on, but make sure you test the glue on the back of the stamp to make sure it won't damage the foam.
Step 4: Add a Handle
If your foam didn't come with a handle, you should add one now. The easiest way is to just cut out some finger holes in the back of the foam. My foam came with holes, so I didn't need to make a handle.