IMPORTANT!!! These coasters are all hand made originals and no two are alike!! An Abstract of the entire state of Michigan, acid oxidized on heavy gauge copper using a 10 day 42 step process. The copper sits on 3/8" slate and is sealed with multiple layers of commercial grade bar top epoxy. This stops any further oxidation and protects your artwork for future generations. Rubber feet protect your surfaces from abrasions. These weigh almost a pound each!