Styrofoam when heated in the oven will shrink slightly and become hard. You must use a low setting to achieve this. I usually start at about 170 degrees and increase the temperature in 5 degree intervals a little at a time.
Transfer a design to the Styrofoam using graphite or carbon paper and a very light touch. If you press to hard you will leave marks in the Styrofoam. This may be a desirable effect depending on your design. Paint your design with the acrylic paint. Cut out the ornament. If you wish to put a ribbon in for hanging, punch a hole at the top before you shrink it.
Place the ornament on a floured cookie sheet and place it in the oven. The shrink time will vary depending on the size of the piece and your oven.
You can use these for gift tags, earrings, pins etc...