Circa 2000. Here's a set of 4 Nature Stone Coasters distributed by Conimar of Ocala, Florida and manufactured in the U.S.A. and China. They have a cork bottom. I really don't understand the "magic" of these coasters. They seem to just suck up all kinds of water from drinking glasses. Where exactly the moisture goes is a mystery. If you need some really good coasters, get some of these Stoneware ones, whether Coke brand or something else. They work great in keeping water off tables.