The ophthalmic coasters are hand-printed Boticinno tumbled marble. Each tile in the set of 4 coasters has its own unique design inspired by vintage patents and drawings. The set includes a convenient rustic holder. They are crafted in North Carolina.Please note that the coasters are unsealed for maximum absorbency. However, they can be sealed with a clear sealant, ideally in a matter or satin finish, available at many hardware stores.