Here's what you'll need: a small bar of oven bake clay (Michael's and Joann Fabrics carry the 2 oz. bars), a bag of wooden craft sticks (also available at Michael's and Joann), Mod Podge, and glitter.
Roll a small (about 1 inch) ball of clay (I used almost 1/2 of a 2 oz. package) and insert craft sticks using the method described here. Once the craft sticks are inserted, put the whole thing on a cookie sheet and bake in the oven at 275° F for 1 hour. (The directions say to bake it 15 minutes for every 1/4 inch of thickness. Since my clay ball was about 1 inch across I had to bake it 4 times longer. Adjust the cooking time if your ball is larger or smaller than 1 inch.)
When it is finished baking, let the ball cool completely before adding glitter. I skipped the painting step this time around, but it does help conceal spots where the glitter isn't thick enough, so I'd recommend painting it first. Then use a paintbrush to apply Mod Podge, add glitter, and put it out where you can admire it everyday!
Originally I intended to paint my imitation urchin silver, but I really liked the glittery ones I made for Christmas, so I decided to use this dark blue glitter I found at Michael's. I think these would look cool though with any color glittery, metallic, or even neon paint! The next time you see my shelves they might just be covered in a rainbow of spiky spheres...