We have all done this at some point in our lives. I remember doing it in grade school more than once. It doesn't take a crafting genius but the kids think it's fun. So do I!
a paper bag
1. I cut up a paper grocery bag and used that for protection under and over my layers of wax paper. You don't want wax on your iron or ironing board. Keep your crayon shavings away from the edges of your wax paper and you shouldn't have a problem.
2. Layer paper bag then wax paper.
3. Peel the paper off your crayon and sharpen away.
5. With a warm iron make a couple of passes then check your progress. It doesn't take much heat to melt the crayon.
6. Let it cool a bit.
8. Cut out.
This photo shows the result of a lot of crayon shavings.
Here is the shamrock template I used. Print it different sizes for a variety of shamrocks.