1. Rubber Mallet
2. Bottle Caps
4. Folded Cardboard
Step 1: Bend Edges Outward
First take the pliers and bend the edges of the bottle cap outward. Make sure it is even all the way around. I like to bend up on every other indention. Try not to scratch the paint on the bottle cap, but don't worry that much about it, sometimes some scratches make it look tuff!
Step 2: Place in Center of Folded Cardboard
Now place the bottle cap in the center of the inside part of the cardboard face up. Fold the cardboard over, feeling with your hand to get a good idea of where the bottle cap is located.
Step 3: Strike With Rubber Mallet
Then strike the top of the cardboard with the rubber mallet in a circular motion. Feel around the cardboard for raised edges and strike again until they feel completely flattened.
Step 4: Remove From Cardboard and Crimp Edges
Last you're going to remove the bottle cap from the cardboard. Take your pliers and crimp the edges so that they are nice and flat, making a few rotations around the bottle cap. And that's it you're done! You now have a fully flattened bottle cap, ready to be used in your awesome crafting projects.